Revert "Adding main thread binder tracing in development build."

Revert submission 23482347-launcher-binder-tracing

Reason for revert: Broken Build 10242119 on git_master on errorprone b/285434612

Reverted changes: /q/submissionid:23482347-launcher-binder-tracing

Change-Id: Id9726474265e839a59d6eb34822e7a86d40f0fc9
diff --git a/quickstep/src/com/android/launcher3/uioverrides/DejankBinderTracker.java b/quickstep/src/com/android/launcher3/uioverrides/DejankBinderTracker.java
new file mode 100644
index 0000000..d8aa235
--- /dev/null
+++ b/quickstep/src/com/android/launcher3/uioverrides/DejankBinderTracker.java
@@ -0,0 +1,159 @@
+/**
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.launcher3.uioverrides;
+
+import static android.os.IBinder.FLAG_ONEWAY;
+
+import android.os.Binder;
+import android.os.Build;
+import android.os.IBinder;
+import android.os.Looper;
+import android.os.RemoteException;
+import android.util.Log;
+
+import androidx.annotation.MainThread;
+
+import java.util.HashSet;
+import java.util.Locale;
+import java.util.function.BiConsumer;
+import java.util.function.Supplier;
+
+/**
+ * A binder proxy transaction listener for tracking non-whitelisted binder calls.
+ */
+public class DejankBinderTracker implements Binder.ProxyTransactListener {
+    private static final String TAG = "DejankBinderTracker";
+
+    private static final Object sLock = new Object();
+    private static final HashSet<String> sWhitelistedFrameworkClasses = new HashSet<>();
+    static {
+        // Common IPCs that are ok to block the main thread.
+        sWhitelistedFrameworkClasses.add("android.view.IWindowSession");
+        sWhitelistedFrameworkClasses.add("android.os.IPowerManager");
+    }
+    private static boolean sTemporarilyIgnoreTracking = false;
+
+    // Used by the client to limit binder tracking to specific regions
+    private static boolean sTrackingAllowed = false;
+
+    private BiConsumer<String, Integer> mUnexpectedTransactionCallback;
+    private boolean mIsTracking = false;
+
+    /**
+     * Temporarily ignore blocking binder calls for the duration of this {@link Runnable}.
+     */
+    @MainThread
+    public static void whitelistIpcs(Runnable runnable) {
+        sTemporarilyIgnoreTracking = true;
+        runnable.run();
+        sTemporarilyIgnoreTracking = false;
+    }
+
+    /**
+     * Temporarily ignore blocking binder calls for the duration of this {@link Supplier}.
+     */
+    @MainThread
+    public static <T> T whitelistIpcs(Supplier<T> supplier) {
+        sTemporarilyIgnoreTracking = true;
+        T value = supplier.get();
+        sTemporarilyIgnoreTracking = false;
+        return value;
+    }
+
+    /**
+     * Enables binder tracking during a test.
+     */
+    @MainThread
+    public static void allowBinderTrackingInTests() {
+        sTrackingAllowed = true;
+    }
+
+    /**
+     * Disables binder tracking during a test.
+     */
+    @MainThread
+    public static void disallowBinderTrackingInTests() {
+        sTrackingAllowed = false;
+    }
+
+    public DejankBinderTracker(BiConsumer<String, Integer> unexpectedTransactionCallback) {
+        mUnexpectedTransactionCallback = unexpectedTransactionCallback;
+    }
+
+    @MainThread
+    public void startTracking() {
+        if (!Build.TYPE.toLowerCase(Locale.ROOT).contains("debug")
+                && !Build.TYPE.toLowerCase(Locale.ROOT).equals("eng")) {
+            Log.wtf(TAG, "Unexpected use of binder tracker in non-debug build", new Exception());
+            return;
+        }
+        if (mIsTracking) {
+            return;
+        }
+        mIsTracking = true;
+        Binder.setProxyTransactListener(this);
+    }
+
+    @MainThread
+    public void stopTracking() {
+        if (!mIsTracking) {
+            return;
+        }
+        mIsTracking = false;
+        Binder.setProxyTransactListener(null);
+    }
+
+    // Override the hidden Binder#onTransactStarted method
+    public synchronized Object onTransactStarted(IBinder binder, int transactionCode, int flags) {
+        if (!mIsTracking
+                || !sTrackingAllowed
+                || sTemporarilyIgnoreTracking
+                || (flags & FLAG_ONEWAY) == FLAG_ONEWAY
+                || !isMainThread()) {
+            return null;
+        }
+
+        String descriptor;
+        try {
+            descriptor = binder.getInterfaceDescriptor();
+            if (sWhitelistedFrameworkClasses.contains(descriptor)) {
+                return null;
+            }
+        } catch (RemoteException e) {
+            e.printStackTrace();
+            descriptor = binder.getClass().getSimpleName();
+        }
+
+        mUnexpectedTransactionCallback.accept(descriptor, transactionCode);
+        return null;
+    }
+
+    @Override
+    public Object onTransactStarted(IBinder binder, int transactionCode) {
+        // Do nothing
+        return null;
+    }
+
+    @Override
+    public void onTransactEnded(Object session) {
+        // Do nothing
+    }
+
+    public static boolean isMainThread() {
+        return Thread.currentThread() == Looper.getMainLooper().getThread();
+    }
+}
diff --git a/quickstep/src/com/android/quickstep/AbsSwipeUpHandler.java b/quickstep/src/com/android/quickstep/AbsSwipeUpHandler.java
index bf4896d..2b92188 100644
--- a/quickstep/src/com/android/quickstep/AbsSwipeUpHandler.java
+++ b/quickstep/src/com/android/quickstep/AbsSwipeUpHandler.java
@@ -112,7 +112,6 @@
 import com.android.launcher3.uioverrides.QuickstepLauncher;
 import com.android.launcher3.util.ActivityLifecycleCallbacksAdapter;
 import com.android.launcher3.util.DisplayController;
-import com.android.launcher3.util.SafeCloseable;
 import com.android.launcher3.util.TraceHelper;
 import com.android.launcher3.util.VibratorWrapper;
 import com.android.launcher3.util.WindowBounds;
@@ -588,7 +587,7 @@
         if (mWasLauncherAlreadyVisible) {
             mStateCallback.setState(STATE_LAUNCHER_DRAWN);
         } else {
-            SafeCloseable traceToken = TraceHelper.INSTANCE.beginAsyncSection("WTS-init");
+            Object traceToken = TraceHelper.INSTANCE.beginSection("WTS-init");
             View dragLayer = activity.getDragLayer();
             dragLayer.getViewTreeObserver().addOnDrawListener(new OnDrawListener() {
                 boolean mHandled = false;
@@ -600,7 +599,7 @@
                     }
                     mHandled = true;
 
-                    traceToken.close();
+                    TraceHelper.INSTANCE.endSection(traceToken);
                     dragLayer.post(() ->
                             dragLayer.getViewTreeObserver().removeOnDrawListener(this));
                     if (activity != mActivity) {
@@ -682,10 +681,11 @@
     private void initializeLauncherAnimationController() {
         buildAnimationController();
 
-        try (SafeCloseable c = TraceHelper.INSTANCE.allowIpcs("logToggleRecents")) {
-            LatencyTracker.getInstance(mContext).logAction(LatencyTracker.ACTION_TOGGLE_RECENTS,
-                    (int) (mLauncherFrameDrawnTime - mTouchTimeMs));
-        }
+        Object traceToken = TraceHelper.INSTANCE.beginSection("logToggleRecents",
+                TraceHelper.FLAG_IGNORE_BINDERS);
+        LatencyTracker.getInstance(mContext).logAction(LatencyTracker.ACTION_TOGGLE_RECENTS,
+                (int) (mLauncherFrameDrawnTime - mTouchTimeMs));
+        TraceHelper.INSTANCE.endSection(traceToken);
 
         // This method is only called when STATE_GESTURE_STARTED is set, so we can enable the
         // high-res thumbnail loader here once we are sure that we will end up in an overview state
@@ -2039,9 +2039,10 @@
 
     private void setScreenshotCapturedState() {
         // If we haven't posted a draw callback, set the state immediately.
-        TraceHelper.INSTANCE.beginSection(SCREENSHOT_CAPTURED_EVT);
+        Object traceToken = TraceHelper.INSTANCE.beginSection(SCREENSHOT_CAPTURED_EVT,
+                TraceHelper.FLAG_CHECK_FOR_RACE_CONDITIONS);
         mStateCallback.setStateOnUiThread(STATE_SCREENSHOT_CAPTURED);
-        TraceHelper.INSTANCE.endSection();
+        TraceHelper.INSTANCE.endSection(traceToken);
     }
 
     private void finishCurrentTransitionToRecents() {
diff --git a/quickstep/src/com/android/quickstep/BinderTracker.java b/quickstep/src/com/android/quickstep/BinderTracker.java
deleted file mode 100644
index a876cd8..0000000
--- a/quickstep/src/com/android/quickstep/BinderTracker.java
+++ /dev/null
@@ -1,187 +0,0 @@
-/**
- * Copyright (C) 2023 The Android Open Source Project
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package com.android.quickstep;
-
-import static android.os.IBinder.FLAG_ONEWAY;
-
-import android.os.Binder;
-import android.os.Binder.ProxyTransactListener;
-import android.os.IBinder;
-import android.os.Looper;
-import android.os.RemoteException;
-import android.os.Trace;
-import android.util.Log;
-
-import androidx.annotation.Nullable;
-
-import com.android.launcher3.util.SafeCloseable;
-import com.android.launcher3.util.TraceHelper;
-
-import java.util.LinkedList;
-import java.util.Set;
-import java.util.function.Consumer;
-
-import kotlin.random.Random;
-
-/**
- * A binder proxy transaction listener for tracking binder calls on main thread.
- */
-public class BinderTracker {
-
-    private static final String TAG = "BinderTracker";
-
-    // Common IPCs that are ok to block the main thread.
-    private static final Set<String> sAllowedFrameworkClasses = Set.of(
-            "android.view.IWindowSession",
-            "android.os.IPowerManager",
-            "android.os.IServiceManager");
-
-    /**
-     * Starts tracking binder class and returns a {@link SafeCloseable} to end tracking
-     */
-    public static SafeCloseable startTracking(Consumer<BinderCallSite> callback) {
-        TraceHelper current = TraceHelper.INSTANCE;
-
-        TraceHelperExtension helper = new TraceHelperExtension(callback);
-        TraceHelper.INSTANCE = helper;
-        Binder.setProxyTransactListener(helper);
-
-        return () -> {
-            Binder.setProxyTransactListener(null);
-            TraceHelper.INSTANCE = current;
-        };
-    }
-
-    private static final LinkedList<String> mMainThreadTraceStack = new LinkedList<>();
-    private static final LinkedList<String> mMainThreadIgnoreIpcStack = new LinkedList<>();
-
-    private static class TraceHelperExtension extends TraceHelper implements ProxyTransactListener {
-
-        private final Consumer<BinderCallSite> mUnexpectedTransactionCallback;
-
-        TraceHelperExtension(Consumer<BinderCallSite> unexpectedTransactionCallback) {
-            mUnexpectedTransactionCallback = unexpectedTransactionCallback;
-        }
-
-        @Override
-        public void beginSection(String sectionName) {
-            if (isMainThread()) {
-                mMainThreadTraceStack.add(sectionName);
-            }
-            super.beginSection(sectionName);
-        }
-
-        @Override
-        public SafeCloseable beginAsyncSection(String sectionName) {
-            if (!isMainThread()) {
-                return super.beginAsyncSection(sectionName);
-            }
-
-            mMainThreadTraceStack.add(sectionName);
-            int cookie = Random.Default.nextInt();
-            Trace.beginAsyncSection(sectionName, cookie);
-            return () -> {
-                Trace.endAsyncSection(sectionName, cookie);
-                mMainThreadTraceStack.remove(sectionName);
-            };
-        }
-
-        @Override
-        public void endSection() {
-            super.endSection();
-            if (isMainThread()) {
-                mMainThreadTraceStack.pollLast();
-            }
-        }
-
-        @Override
-        public SafeCloseable allowIpcs(String rpcName) {
-            if (!isMainThread()) {
-                return super.allowIpcs(rpcName);
-            }
-
-            mMainThreadTraceStack.add(rpcName);
-            mMainThreadIgnoreIpcStack.add(rpcName);
-            int cookie = Random.Default.nextInt();
-            Trace.beginAsyncSection(rpcName, cookie);
-            return () -> {
-                Trace.endAsyncSection(rpcName, cookie);
-                mMainThreadTraceStack.remove(rpcName);
-                mMainThreadIgnoreIpcStack.remove(rpcName);
-            };
-        }
-
-        @Override
-        public Object onTransactStarted(IBinder binder, int transactionCode, int flags) {
-            if (!isMainThread() || (flags & FLAG_ONEWAY) == FLAG_ONEWAY) {
-                return null;
-            }
-
-            String ipcBypass = mMainThreadIgnoreIpcStack.peekLast();
-            String descriptor;
-            try {
-                descriptor = binder.getInterfaceDescriptor();
-                if (sAllowedFrameworkClasses.contains(descriptor)) {
-                    return null;
-                }
-            } catch (RemoteException e) {
-                Log.e(TAG, "Error getting IPC descriptor", e);
-                descriptor = binder.getClass().getSimpleName();
-            }
-
-            if (ipcBypass == null) {
-                mUnexpectedTransactionCallback.accept(new BinderCallSite(
-                        mMainThreadTraceStack.peekLast(), descriptor, transactionCode));
-            } else {
-                Log.d(TAG, "MainThread-IPC " + descriptor + " ignored due to " + ipcBypass);
-            }
-            return null;
-        }
-
-        @Override
-        public Object onTransactStarted(IBinder binder, int transactionCode) {
-            // Do nothing
-            return null;
-        }
-
-        @Override
-        public void onTransactEnded(Object session) {
-            // Do nothing
-        }
-    }
-
-    private static boolean isMainThread() {
-        return Thread.currentThread() == Looper.getMainLooper().getThread();
-    }
-
-    /**
-     * Information about a binder call
-     */
-    public static class BinderCallSite {
-
-        @Nullable
-        public final String activeTrace;
-        public final String descriptor;
-        public final int transactionCode;
-
-        BinderCallSite(String activeTrace, String descriptor, int transactionCode) {
-            this.activeTrace = activeTrace;
-            this.descriptor = descriptor;
-            this.transactionCode = transactionCode;
-        }
-    }
-}
diff --git a/quickstep/src/com/android/quickstep/InstantAppResolverImpl.java b/quickstep/src/com/android/quickstep/InstantAppResolverImpl.java
index 529213c..7638541 100644
--- a/quickstep/src/com/android/quickstep/InstantAppResolverImpl.java
+++ b/quickstep/src/com/android/quickstep/InstantAppResolverImpl.java
@@ -16,13 +16,10 @@
 
 package com.android.quickstep;
 
-import android.app.ActivityThread;
 import android.content.ComponentName;
 import android.content.Context;
 import android.content.pm.ApplicationInfo;
 import android.content.pm.PackageManager;
-import android.os.RemoteException;
-import android.util.Log;
 
 import com.android.launcher3.model.data.AppInfo;
 import com.android.launcher3.util.InstantAppResolver;
@@ -52,14 +49,4 @@
         ComponentName cn = info.getTargetComponent();
         return cn != null && cn.getClassName().equals(COMPONENT_CLASS_MARKER);
     }
-
-    @Override
-    public boolean isInstantApp(String packageName, int userId) {
-        try {
-            return ActivityThread.getPackageManager().isInstantApp(packageName, userId);
-        } catch (RemoteException e) {
-            Log.e(TAG, "Failed to determine whether package is instant app " + packageName, e);
-            return false;
-        }
-    }
 }
diff --git a/quickstep/src/com/android/quickstep/QuickstepProcessInitializer.java b/quickstep/src/com/android/quickstep/QuickstepProcessInitializer.java
index 128b045..5f589bf 100644
--- a/quickstep/src/com/android/quickstep/QuickstepProcessInitializer.java
+++ b/quickstep/src/com/android/quickstep/QuickstepProcessInitializer.java
@@ -60,10 +60,5 @@
         // Elevate GPU priority for Quickstep and Remote animations.
         ThreadedRenderer.setContextPriority(
                 ThreadedRenderer.EGL_CONTEXT_PRIORITY_HIGH_IMG);
-
-        if (BuildConfig.IS_STUDIO_BUILD) {
-            BinderTracker.startTracking(call ->  Log.e("BinderCall",
-                    call.descriptor + " called on mainthread under " + call.activeTrace));
-        }
     }
 }
diff --git a/quickstep/src/com/android/quickstep/TaskShortcutFactory.java b/quickstep/src/com/android/quickstep/TaskShortcutFactory.java
index 810c028..8135238 100644
--- a/quickstep/src/com/android/quickstep/TaskShortcutFactory.java
+++ b/quickstep/src/com/android/quickstep/TaskShortcutFactory.java
@@ -393,12 +393,11 @@
         @Override
         public List<SystemShortcut> getShortcuts(BaseDraggingActivity activity,
                 TaskIdAttributeContainer taskContainer) {
-            Task t = taskContainer.getTask();
-            return InstantAppResolver.newInstance(activity).isInstantApp(
-                    t.getTopComponent().getPackageName(), t.getKey().userId)
-                    ? Collections.singletonList(new SystemShortcut.Install(activity,
-                            taskContainer.getItemInfo(), taskContainer.getTaskView()))
-                    : null;
+            return InstantAppResolver.newInstance(activity).isInstantApp(activity,
+                    taskContainer.getTask().getTopComponent().getPackageName()) ?
+                    Collections.singletonList(new SystemShortcut.Install(activity,
+                            taskContainer.getItemInfo(), taskContainer.getTaskView())) :
+                    null;
         }
     };
 
diff --git a/quickstep/src/com/android/quickstep/TaskUtils.java b/quickstep/src/com/android/quickstep/TaskUtils.java
index 80a449b..67360c4 100644
--- a/quickstep/src/com/android/quickstep/TaskUtils.java
+++ b/quickstep/src/com/android/quickstep/TaskUtils.java
@@ -33,7 +33,6 @@
 import com.android.launcher3.pm.UserCache;
 import com.android.launcher3.util.ComponentKey;
 import com.android.launcher3.util.PackageManagerHelper;
-import com.android.launcher3.util.TraceHelper;
 import com.android.systemui.shared.recents.model.Task;
 import com.android.systemui.shared.system.ActivityManagerWrapper;
 
@@ -52,8 +51,7 @@
      * TODO: remove this once we switch to getting the icon and label from IconCache.
      */
     public static CharSequence getTitle(Context context, Task task) {
-        return TraceHelper.allowIpcs("TaskUtils.getTitle", () ->
-                getTitle(context, task.key.userId, task.getTopComponent().getPackageName()));
+        return getTitle(context, task.key.userId, task.getTopComponent().getPackageName());
     }
 
     public static CharSequence getTitle(
diff --git a/quickstep/src/com/android/quickstep/TouchInteractionService.java b/quickstep/src/com/android/quickstep/TouchInteractionService.java
index a060c7c..8d05fa9 100644
--- a/quickstep/src/com/android/quickstep/TouchInteractionService.java
+++ b/quickstep/src/com/android/quickstep/TouchInteractionService.java
@@ -102,7 +102,6 @@
 import com.android.launcher3.util.DisplayController;
 import com.android.launcher3.util.LockedUserState;
 import com.android.launcher3.util.OnboardingPrefs;
-import com.android.launcher3.util.SafeCloseable;
 import com.android.launcher3.util.TraceHelper;
 import com.android.quickstep.inputconsumers.AccessibilityInputConsumer;
 import com.android.quickstep.inputconsumers.AssistantInputConsumer;
@@ -655,7 +654,8 @@
             return;
         }
 
-        SafeCloseable traceToken = TraceHelper.INSTANCE.allowIpcs("TIS.onInputEvent");
+        Object traceToken = TraceHelper.INSTANCE.beginFlagsOverride(
+                TraceHelper.FLAG_ALLOW_BINDER_TRACKING);
 
         final int action = event.getActionMasked();
         // Note this will create a new consumer every mouse click, as after ACTION_UP from the click
@@ -751,7 +751,7 @@
         if (cleanUpConsumer) {
             reset();
         }
-        traceToken.close();
+        TraceHelper.INSTANCE.endFlagsOverride(traceToken);
         ProtoTracer.INSTANCE.get(this).scheduleFrameUpdate();
     }
 
diff --git a/quickstep/src/com/android/quickstep/inputconsumers/OtherActivityInputConsumer.java b/quickstep/src/com/android/quickstep/inputconsumers/OtherActivityInputConsumer.java
index 10c6316..5b27f9b 100644
--- a/quickstep/src/com/android/quickstep/inputconsumers/OtherActivityInputConsumer.java
+++ b/quickstep/src/com/android/quickstep/inputconsumers/OtherActivityInputConsumer.java
@@ -28,6 +28,7 @@
 import static com.android.launcher3.Utilities.EDGE_NAV_BAR;
 import static com.android.launcher3.Utilities.squaredHypot;
 import static com.android.launcher3.util.Executors.MAIN_EXECUTOR;
+import static com.android.launcher3.util.TraceHelper.FLAG_CHECK_FOR_RACE_CONDITIONS;
 import static com.android.launcher3.util.VelocityUtils.PX_PER_MS;
 import static com.android.quickstep.util.ActiveGestureLog.INTENT_EXTRA_LOG_TRACE_ID;
 
@@ -228,7 +229,8 @@
                 // Until we detect the gesture, handle events as we receive them
                 mInputEventReceiver.setBatchingEnabled(false);
 
-                TraceHelper.INSTANCE.beginSection(DOWN_EVT);
+                Object traceToken = TraceHelper.INSTANCE.beginSection(DOWN_EVT,
+                        FLAG_CHECK_FOR_RACE_CONDITIONS);
                 mActivePointerId = ev.getPointerId(0);
                 mDownPos.set(ev.getX(), ev.getY());
                 mLastPos.set(mDownPos);
@@ -239,7 +241,7 @@
                     startTouchTrackingForWindowAnimation(ev.getEventTime());
                 }
 
-                TraceHelper.INSTANCE.endSection();
+                TraceHelper.INSTANCE.endSection(traceToken);
                 break;
             }
             case ACTION_POINTER_DOWN: {
@@ -415,7 +417,8 @@
      * the animation can still be running.
      */
     private void finishTouchTracking(MotionEvent ev) {
-        TraceHelper.INSTANCE.beginSection(UP_EVT);
+        Object traceToken = TraceHelper.INSTANCE.beginSection(UP_EVT,
+                FLAG_CHECK_FOR_RACE_CONDITIONS);
 
         if (mPassedWindowMoveSlop && mInteractionHandler != null) {
             if (ev.getActionMasked() == ACTION_CANCEL) {
@@ -452,7 +455,7 @@
             onInteractionGestureFinished();
         }
         cleanupAfterGesture();
-        TraceHelper.INSTANCE.endSection();
+        TraceHelper.INSTANCE.endSection(traceToken);
     }
 
     private void cleanupAfterGesture() {
diff --git a/quickstep/src/com/android/quickstep/util/BinderTracker.java b/quickstep/src/com/android/quickstep/util/BinderTracker.java
new file mode 100644
index 0000000..cb04e5b
--- /dev/null
+++ b/quickstep/src/com/android/quickstep/util/BinderTracker.java
@@ -0,0 +1,63 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.quickstep.util;
+
+import android.os.Binder;
+import android.os.IBinder;
+import android.os.Looper;
+import android.util.Log;
+
+import com.android.launcher3.config.FeatureFlags;
+
+/**
+ * Utility class to test and check binder calls during development.
+ */
+public class BinderTracker {
+
+    private static final String TAG = "BinderTracker";
+
+    public static void start() {
+        if (!FeatureFlags.IS_STUDIO_BUILD) {
+            Log.wtf(TAG, "Accessing tracker in released code.", new Exception());
+            return;
+        }
+
+        Binder.setProxyTransactListener(new Tracker());
+    }
+
+    public static void stop() {
+        if (!FeatureFlags.IS_STUDIO_BUILD) {
+            Log.wtf(TAG, "Accessing tracker in released code.", new Exception());
+            return;
+        }
+        Binder.setProxyTransactListener(null);
+    }
+
+    private static class Tracker implements Binder.ProxyTransactListener {
+
+        @Override
+        public Object onTransactStarted(IBinder iBinder, int code) {
+            if (Looper.myLooper() == Looper.getMainLooper()) {
+                Log.e(TAG, "Binder call on ui thread", new Exception());
+            }
+            return null;
+        }
+
+        @Override
+        public void onTransactEnded(Object session) { }
+    }
+}
diff --git a/quickstep/src/com/android/quickstep/util/TaskViewSimulator.java b/quickstep/src/com/android/quickstep/util/TaskViewSimulator.java
index 7f035a2..f8893bd 100644
--- a/quickstep/src/com/android/quickstep/util/TaskViewSimulator.java
+++ b/quickstep/src/com/android/quickstep/util/TaskViewSimulator.java
@@ -112,7 +112,8 @@
         mContext = context;
         mSizeStrategy = sizeStrategy;
 
-        mOrientationState = TraceHelper.allowIpcs("TaskViewSimulator.init",
+        // TODO(b/187074722): Don't create this per-TaskViewSimulator
+        mOrientationState = TraceHelper.allowIpcs("",
                 () -> new RecentsOrientedState(context, sizeStrategy, i -> { }));
         mOrientationState.setGestureActive(true);
         mCurrentFullscreenParams = new FullscreenDrawParams(context);
diff --git a/quickstep/src/com/android/quickstep/views/TaskView.java b/quickstep/src/com/android/quickstep/views/TaskView.java
index 46dd94b..200252a 100644
--- a/quickstep/src/com/android/quickstep/views/TaskView.java
+++ b/quickstep/src/com/android/quickstep/views/TaskView.java
@@ -32,7 +32,6 @@
 import static com.android.launcher3.util.SplitConfigurationOptions.STAGE_POSITION_BOTTOM_OR_RIGHT;
 import static com.android.launcher3.util.SplitConfigurationOptions.STAGE_POSITION_UNDEFINED;
 import static com.android.launcher3.util.SplitConfigurationOptions.getLogEventForPosition;
-import static com.android.quickstep.TaskOverlayFactory.getEnabledShortcuts;
 import static com.android.quickstep.util.BorderAnimator.DEFAULT_BORDER_COLOR;
 
 import static java.lang.annotation.RetentionPolicy.SOURCE;
@@ -89,7 +88,6 @@
 import com.android.launcher3.util.RunnableList;
 import com.android.launcher3.util.SplitConfigurationOptions;
 import com.android.launcher3.util.SplitConfigurationOptions.SplitPositionOption;
-import com.android.launcher3.util.TraceHelper;
 import com.android.launcher3.util.TransformingTouchDelegate;
 import com.android.launcher3.util.ViewPool.Reusable;
 import com.android.quickstep.RecentsModel;
@@ -1558,8 +1556,8 @@
             if (taskContainer == null) {
                 continue;
             }
-            for (SystemShortcut s : TraceHelper.allowIpcs(
-                    "TV.a11yInfo", () -> getEnabledShortcuts(this, taskContainer))) {
+            for (SystemShortcut s : TaskOverlayFactory.getEnabledShortcuts(this,
+                    taskContainer)) {
                 info.addAction(s.createAccessibilityAction(context));
             }
         }
@@ -1596,7 +1594,7 @@
             if (taskContainer == null) {
                 continue;
             }
-            for (SystemShortcut s : getEnabledShortcuts(this,
+            for (SystemShortcut s : TaskOverlayFactory.getEnabledShortcuts(this,
                     taskContainer)) {
                 if (s.hasHandlerForAction(action)) {
                     s.onClick(this);
diff --git a/quickstep/tests/src/com/android/quickstep/StartLauncherViaGestureTests.java b/quickstep/tests/src/com/android/quickstep/StartLauncherViaGestureTests.java
index 5127190..df5303f 100644
--- a/quickstep/tests/src/com/android/quickstep/StartLauncherViaGestureTests.java
+++ b/quickstep/tests/src/com/android/quickstep/StartLauncherViaGestureTests.java
@@ -20,6 +20,7 @@
 import androidx.test.runner.AndroidJUnit4;
 
 import com.android.launcher3.ui.TaplTestsLauncher3;
+import com.android.launcher3.util.RaceConditionReproducer;
 import com.android.quickstep.NavigationModeSwitchRule.NavigationModeSwitch;
 
 import org.junit.Before;
@@ -44,6 +45,18 @@
         startTestActivity(2);
     }
 
+    private void runTest(String... eventSequence) {
+        final RaceConditionReproducer eventProcessor = new RaceConditionReproducer(eventSequence);
+
+        // Destroy Launcher activity.
+        closeLauncherActivity();
+
+        // The test action.
+        eventProcessor.startIteration();
+        mLauncher.goHome();
+        eventProcessor.finishIteration();
+    }
+
     @Ignore
     @Test
     @NavigationModeSwitch
diff --git a/res/drawable/ic_wallpaper.xml b/res/drawable/ic_wallpaper.xml
new file mode 100644
index 0000000..9543f88
--- /dev/null
+++ b/res/drawable/ic_wallpaper.xml
@@ -0,0 +1,27 @@
+<!--
+   Copyright (C) 2016 The Android Open Source Project
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+    you may not use this file except in compliance with the License.
+    You may obtain a copy of the License at
+
+         http://www.apache.org/licenses/LICENSE-2.0
+
+    Unless required by applicable law or agreed to in writing, software
+    distributed under the License is distributed on an "AS IS" BASIS,
+    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+    See the License for the specific language governing permissions and
+    limitations under the License.
+-->
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+        android:width="@dimen/options_menu_icon_size"
+        android:height="@dimen/options_menu_icon_size"
+        android:viewportWidth="24.0"
+        android:viewportHeight="24.0"
+        android:tint="?android:attr/textColorPrimary">
+    <path
+        android:fillColor="@android:color/white"
+        android:pathData="M9,12.71l2.14,2.58l3-3.87L18,16.57H6L9,12.71z M5,5h6V3H5C3.9,3,3,3.9,3,5v6h2V5z M19,19h-6v2h6c1.1,0,2-0.9,2-2v-6h-2V19z
+            M5,19v-6H3v6c0,1.1,0.9,2,2,2h6v-2H5z M19,5v6h2V5c0-1.1-0.9-2-2-2h-6v2H19z M16,9c0.55,0,1-0.45,1-1s-0.45-1-1-1
+            c-0.55,0-1,0.45-1,1S15.45,9,16,9z"/>
+</vector>
diff --git a/res/values/config.xml b/res/values/config.xml
index 83f840d..5a6698b 100644
--- a/res/values/config.xml
+++ b/res/values/config.xml
@@ -102,6 +102,8 @@
 
     <!-- Default packages -->
     <string name="wallpaper_picker_package" translatable="false"></string>
+    <string name="custom_activity_picker" translatable="false">
+        com.android.customization.picker.CustomizationPickerActivity</string>
     <string name="local_colors_extraction_class" translatable="false"></string>
     <string name="search_session_manager_class" translatable="false"></string>
 
diff --git a/res/values/strings.xml b/res/values/strings.xml
index 1b46b4d..c2eb373 100644
--- a/res/values/strings.xml
+++ b/res/values/strings.xml
@@ -250,6 +250,8 @@
 
     <!-- Strings for the customization mode -->
     <!-- Text for wallpaper change button [CHAR LIMIT=30]-->
+    <string name="wallpaper_button_text">Wallpapers</string>
+    <!-- Text for wallpaper change button [CHAR LIMIT=30]-->
     <string name="styles_wallpaper_button_text">Wallpaper &amp; style</string>
     <!-- Text for edit home screen button [CHAR LIMIT=30]-->
     <string name="edit_home_screen">Edit Home Screen</string>
diff --git a/src/com/android/launcher3/Launcher.java b/src/com/android/launcher3/Launcher.java
index ac46c82..db5a27a 100644
--- a/src/com/android/launcher3/Launcher.java
+++ b/src/com/android/launcher3/Launcher.java
@@ -442,7 +442,8 @@
             Trace.beginAsyncSection(DISPLAY_ALL_APPS_TRACE_METHOD_NAME,
                     DISPLAY_ALL_APPS_TRACE_COOKIE);
         }
-        TraceHelper.INSTANCE.beginSection(ON_CREATE_EVT);
+        Object traceToken = TraceHelper.INSTANCE.beginSection(ON_CREATE_EVT,
+                TraceHelper.FLAG_UI_EVENT);
         if (DEBUG_STRICT_MODE) {
             StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder()
                     .detectDiskReads()
@@ -575,7 +576,7 @@
                 LauncherOverlayPlugin.class, false /* allowedMultiple */);
 
         mRotationHelper.initialize();
-        TraceHelper.INSTANCE.endSection();
+        TraceHelper.INSTANCE.endSection(traceToken);
 
         mUserChangedCallbackCloseable = UserCache.INSTANCE.get(this).addUserChangeListener(
                 () -> getStateManager().goToState(NORMAL));
@@ -1073,14 +1074,15 @@
 
     @Override
     protected void onStart() {
-        TraceHelper.INSTANCE.beginSection(ON_START_EVT);
+        Object traceToken = TraceHelper.INSTANCE.beginSection(ON_START_EVT,
+                TraceHelper.FLAG_UI_EVENT);
         super.onStart();
         if (!mDeferOverlayCallbacks) {
             mOverlayManager.onActivityStarted(this);
         }
 
         mAppWidgetHolder.setActivityStarted(true);
-        TraceHelper.INSTANCE.endSection();
+        TraceHelper.INSTANCE.endSection(traceToken);
     }
 
     @Override
@@ -1251,7 +1253,8 @@
 
     @Override
     protected void onResume() {
-        TraceHelper.INSTANCE.beginSection(ON_RESUME_EVT);
+        Object traceToken = TraceHelper.INSTANCE.beginSection(ON_RESUME_EVT,
+                TraceHelper.FLAG_UI_EVENT);
         super.onResume();
 
         if (mDeferOverlayCallbacks) {
@@ -1261,7 +1264,7 @@
         }
 
         DragView.removeAllViews(this);
-        TraceHelper.INSTANCE.endSection();
+        TraceHelper.INSTANCE.endSection(traceToken);
     }
 
     @Override
@@ -1649,7 +1652,7 @@
         if (Utilities.isRunningInTestHarness()) {
             Log.d(TestProtocol.PERMANENT_DIAG_TAG, "Launcher.onNewIntent: " + intent);
         }
-        TraceHelper.INSTANCE.beginSection(ON_NEW_INTENT_EVT);
+        Object traceToken = TraceHelper.INSTANCE.beginSection(ON_NEW_INTENT_EVT);
         super.onNewIntent(intent);
 
         boolean alreadyOnHome = hasWindowFocus() && ((intent.getFlags() &
@@ -1696,7 +1699,7 @@
             showAllAppsWorkTabFromIntent(alreadyOnHome);
         }
 
-        TraceHelper.INSTANCE.endSection();
+        TraceHelper.INSTANCE.endSection(traceToken);
     }
 
     protected void toggleAllAppsFromIntent(boolean alreadyOnHome) {
@@ -2295,7 +2298,7 @@
      * Implementation of the method from LauncherModel.Callbacks.
      */
     public void startBinding() {
-        TraceHelper.INSTANCE.beginSection("startBinding");
+        Object traceToken = TraceHelper.INSTANCE.beginSection("startBinding");
         // Floating panels (except the full widget sheet) are associated with individual icons. If
         // we are starting a fresh bind, close all such panels as all the icons are about
         // to go away.
@@ -2313,7 +2316,7 @@
         if (mHotseat != null) {
             mHotseat.resetLayout(getDeviceProfile().isVerticalBarLayout());
         }
-        TraceHelper.INSTANCE.endSection();
+        TraceHelper.INSTANCE.endSection(traceToken);
     }
 
     @Override
@@ -2566,7 +2569,7 @@
             return view;
         }
 
-        TraceHelper.INSTANCE.beginSection("BIND_WIDGET_id=" + item.appWidgetId);
+        Object traceToken = TraceHelper.INSTANCE.beginSection("BIND_WIDGET_id=" + item.appWidgetId);
 
         try {
             final LauncherAppWidgetProviderInfo appWidgetInfo;
@@ -2696,7 +2699,7 @@
             }
             prepareAppWidget(view, item);
         } finally {
-            TraceHelper.INSTANCE.endSection();
+            TraceHelper.INSTANCE.endSection(traceToken);
         }
 
         return view;
@@ -2789,7 +2792,7 @@
      * Implementation of the method from LauncherModel.Callbacks.
      */
     public void finishBindingItems(IntSet pagesBoundFirst) {
-        TraceHelper.INSTANCE.beginSection("finishBindingItems");
+        Object traceToken = TraceHelper.INSTANCE.beginSection("finishBindingItems");
         mWorkspace.restoreInstanceStateForRemainingPages();
 
         setWorkspaceLoading(false);
@@ -2814,7 +2817,7 @@
                 mDeviceProfile.inv.numFolderColumns * mDeviceProfile.inv.numFolderRows);
         getViewCache().setCacheSize(R.layout.folder_page, 2);
 
-        TraceHelper.INSTANCE.endSection();
+        TraceHelper.INSTANCE.endSection(traceToken);
 
         mWorkspace.removeExtraEmptyScreen(true);
     }
diff --git a/src/com/android/launcher3/model/LoaderTask.java b/src/com/android/launcher3/model/LoaderTask.java
index 73a06b6..d2a8174 100644
--- a/src/com/android/launcher3/model/LoaderTask.java
+++ b/src/com/android/launcher3/model/LoaderTask.java
@@ -201,7 +201,7 @@
             }
         }
 
-        TraceHelper.INSTANCE.beginSection(TAG);
+        Object traceToken = TraceHelper.INSTANCE.beginSection(TAG);
         LoaderMemoryLogger memoryLogger = new LoaderMemoryLogger();
         try (LauncherModel.LoaderTransaction transaction = mApp.getModel().beginLoader(this)) {
             List<ShortcutInfo> allShortcuts = new ArrayList<>();
@@ -325,7 +325,7 @@
             memoryLogger.printLogs();
             throw e;
         }
-        TraceHelper.INSTANCE.endSection();
+        TraceHelper.INSTANCE.endSection(traceToken);
     }
 
     public synchronized void stopLocked() {
diff --git a/src/com/android/launcher3/util/InstantAppResolver.java b/src/com/android/launcher3/util/InstantAppResolver.java
index bdb5e77..6f706d2 100644
--- a/src/com/android/launcher3/util/InstantAppResolver.java
+++ b/src/com/android/launcher3/util/InstantAppResolver.java
@@ -42,7 +42,14 @@
         return false;
     }
 
-    public boolean isInstantApp(String packageName, int userId) {
+    public boolean isInstantApp(Context context, String packageName) {
+        PackageManager packageManager = context.getPackageManager();
+        try {
+            return isInstantApp(packageManager.getPackageInfo(packageName, 0).applicationInfo);
+        } catch (PackageManager.NameNotFoundException e) {
+            Log.e("InstantAppResolver", "Failed to determine whether package is instant app "
+                    + packageName, e);
+        }
         return false;
     }
 }
diff --git a/src/com/android/launcher3/util/PackageManagerHelper.java b/src/com/android/launcher3/util/PackageManagerHelper.java
index 91203a7..1d6bc25 100644
--- a/src/com/android/launcher3/util/PackageManagerHelper.java
+++ b/src/com/android/launcher3/util/PackageManagerHelper.java
@@ -164,6 +164,13 @@
         }
     }
 
+    public static Intent getStyleWallpapersIntent(Context context) {
+        return new Intent(Intent.ACTION_SET_WALLPAPER).setComponent(
+                new ComponentName(context.getString(R.string.wallpaper_picker_package),
+                    context.getString(R.string.custom_activity_picker)
+                ));
+    }
+
     /**
      * Starts the details activity for {@code info}
      */
diff --git a/src/com/android/launcher3/util/TraceHelper.java b/src/com/android/launcher3/util/TraceHelper.java
index d5056ee..c23df77 100644
--- a/src/com/android/launcher3/util/TraceHelper.java
+++ b/src/com/android/launcher3/util/TraceHelper.java
@@ -21,8 +21,6 @@
 
 import java.util.function.Supplier;
 
-import kotlin.random.Random;
-
 /**
  * A wrapper around {@link Trace} to allow better testing.
  *
@@ -38,53 +36,54 @@
     // Temporarily ignore blocking binder calls for this trace.
     public static final int FLAG_IGNORE_BINDERS = 1 << 1;
 
+    public static final int FLAG_CHECK_FOR_RACE_CONDITIONS = 1 << 2;
+
+    public static final int FLAG_UI_EVENT =
+            FLAG_ALLOW_BINDER_TRACKING | FLAG_CHECK_FOR_RACE_CONDITIONS;
+
     /**
      * Static instance of Trace helper, overridden in tests.
      */
     public static TraceHelper INSTANCE = new TraceHelper();
 
     /**
-     * @see Trace#beginSection(String)
+     * @return a token to pass into {@link #endSection(Object)}.
      */
-    public void beginSection(String sectionName) {
+    public Object beginSection(String sectionName) {
+        return beginSection(sectionName, 0);
+    }
+
+    public Object beginSection(String sectionName, int flags) {
         Trace.beginSection(sectionName);
+        return null;
     }
 
     /**
-     * @see Trace#endSection()
+     * @param token the token returned from {@link #beginSection(String, int)}
      */
-    public void endSection() {
+    public void endSection(Object token) {
         Trace.endSection();
     }
 
     /**
-     * @see Trace#beginAsyncSection(String, int)
-     * @return a SafeCloseable that can be used to end the session
+     * Similar to {@link #beginSection} but doesn't add a trace section.
      */
-    public SafeCloseable beginAsyncSection(String sectionName) {
-        int cookie = Random.Default.nextInt();
-        Trace.beginAsyncSection(sectionName, cookie);
-        return () -> Trace.endAsyncSection(sectionName, cookie);
+    public Object beginFlagsOverride(int flags) {
+        return null;
     }
 
-    /**
-     * Returns a SafeCloseable to temporarily ignore blocking binder calls.
-     */
-    public SafeCloseable allowIpcs(String rpcName) {
-        int cookie = Random.Default.nextInt();
-        Trace.beginAsyncSection(rpcName, cookie);
-        return () -> Trace.endAsyncSection(rpcName, cookie);
-    }
+    public void endFlagsOverride(Object token) { }
 
     /**
      * Temporarily ignore blocking binder calls for the duration of this {@link Supplier}.
-     *
-     * Note, new features should be designed to not rely on mainThread RPCs.
      */
     @MainThread
     public static <T> T allowIpcs(String rpcName, Supplier<T> supplier) {
-        try (SafeCloseable c = INSTANCE.allowIpcs(rpcName)) {
+        Object traceToken = INSTANCE.beginSection(rpcName, FLAG_IGNORE_BINDERS);
+        try {
             return supplier.get();
+        } finally {
+            INSTANCE.endSection(traceToken);
         }
     }
 }
diff --git a/src/com/android/launcher3/views/OptionsPopupView.java b/src/com/android/launcher3/views/OptionsPopupView.java
index 55febc7..aebf752 100644
--- a/src/com/android/launcher3/views/OptionsPopupView.java
+++ b/src/com/android/launcher3/views/OptionsPopupView.java
@@ -55,6 +55,7 @@
 import com.android.launcher3.shortcuts.DeepShortcutView;
 import com.android.launcher3.testing.TestLogging;
 import com.android.launcher3.testing.shared.TestProtocol;
+import com.android.launcher3.util.PackageManagerHelper;
 import com.android.launcher3.widget.picker.WidgetsFullSheet;
 
 import java.util.ArrayList;
@@ -189,9 +190,14 @@
      */
     public static ArrayList<OptionItem> getOptions(Launcher launcher) {
         ArrayList<OptionItem> options = new ArrayList<>();
+        boolean styleWallpaperExists = styleWallpapersExists(launcher);
+        int resString = styleWallpaperExists
+                ? R.string.styles_wallpaper_button_text : R.string.wallpaper_button_text;
+        int resDrawable = styleWallpaperExists
+                ? R.drawable.ic_palette : R.drawable.ic_wallpaper;
         options.add(new OptionItem(launcher,
-                R.string.styles_wallpaper_button_text,
-                R.drawable.ic_palette,
+                resString,
+                resDrawable,
                 IGNORE,
                 OptionsPopupView::startWallpaperPicker));
         if (!WidgetsModel.GO_DISABLE_WIDGETS) {
@@ -268,8 +274,12 @@
                 .addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK)
                 .putExtra(EXTRA_WALLPAPER_OFFSET,
                         launcher.getWorkspace().getWallpaperOffsetForCenterPage())
-                .putExtra(EXTRA_WALLPAPER_LAUNCH_SOURCE, "app_launched_launcher")
-                .putExtra(EXTRA_WALLPAPER_FLAVOR, "focus_wallpaper");
+                .putExtra(EXTRA_WALLPAPER_LAUNCH_SOURCE, "app_launched_launcher");
+        if (!styleWallpapersExists(launcher)) {
+            intent.putExtra(EXTRA_WALLPAPER_FLAVOR, "wallpaper_only");
+        } else {
+            intent.putExtra(EXTRA_WALLPAPER_FLAVOR, "focus_wallpaper");
+        }
         String pickerPackage = launcher.getString(R.string.wallpaper_picker_package);
         if (!TextUtils.isEmpty(pickerPackage)) {
             intent.setPackage(pickerPackage);
@@ -312,4 +322,9 @@
             this.clickListener = clickListener;
         }
     }
+
+    private static boolean styleWallpapersExists(Context context) {
+        return context.getPackageManager().resolveActivity(
+                PackageManagerHelper.getStyleWallpapersIntent(context), 0) != null;
+    }
 }
diff --git a/tests/src/com/android/launcher3/util/RaceConditionReproducer.java b/tests/src/com/android/launcher3/util/RaceConditionReproducer.java
new file mode 100644
index 0000000..ed2ec7b
--- /dev/null
+++ b/tests/src/com/android/launcher3/util/RaceConditionReproducer.java
@@ -0,0 +1,500 @@
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.launcher3.util;
+
+import static com.android.launcher3.util.Executors.createAndStartNewLooper;
+
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+
+import android.os.Handler;
+import android.util.Log;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.concurrent.Semaphore;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Event processor for reliably reproducing multithreaded apps race conditions in tests.
+ *
+ * The app notifies us about “events” that happen in its threads. The race condition test runs the
+ * test action multiple times (aka iterations), trying to generate all possible permutations of
+ * these events. It keeps a set of all seen event sequences and steers the execution towards
+ * executing events in previously unseen order. It does it by postponing execution of threads that
+ * would lead to an already seen sequence.
+ *
+ * If an event A occurs before event B in the sequence, this is how execution order looks like:
+ * Events: ... A ... B ...
+ * Events and instructions, guaranteed order:
+ * (instructions executed prior to A) A ... B (instructions executed after B)
+ *
+ * Each iteration has 3 parts (phases).
+ * Phase 1. Picking a previously seen event subsequence that we believe can have previously unseen
+ * continuations. Reproducing this sequence by pausing threads that would lead to other sequences.
+ * Phase 2. Trying to generate previously unseen continuation of the sequence from Phase 1. We need
+ * one new event after that sequence. All threads leading to seen continuations will be postponed
+ * for some short period of time. The phase ends once the new event is registered, or after the
+ * period of time ends (in which case we declare that the sequence can’t have new continuations).
+ * Phase 3. Releasing all threads and letting the test iteration run till its end.
+ *
+ * The iterations end when all seen paths have been declared “uncontinuable”.
+ *
+ * When we register event XXX:enter, we hold all other events until we register XXX:exit.
+ */
+public class RaceConditionReproducer {
+    private static final String TAG = "RaceConditionReproducer";
+
+    private static final boolean ENTER = true;
+    private static final boolean EXIT = false;
+    private static final String ENTER_POSTFIX = "enter";
+    private static final String EXIT_POSTFIX = "exit";
+
+    private static final long SHORT_TIMEOUT_MS = 2000;
+    private static final long LONG_TIMEOUT_MS = 60000;
+    // Handler used to resume postponed events.
+    private static final Handler POSTPONED_EVENT_RESUME_HANDLER =
+            new Handler(createAndStartNewLooper("RaceConditionEventResumer"));
+
+    public static String enterExitEvt(String eventName, boolean isEnter) {
+        return eventName + ":" + (isEnter ? ENTER_POSTFIX : EXIT_POSTFIX);
+    }
+
+    public static String enterEvt(String eventName) {
+        return enterExitEvt(eventName, ENTER);
+    }
+
+    public static String exitEvt(String eventName) {
+        return enterExitEvt(eventName, EXIT);
+    }
+
+    /**
+     * Event in a particular sequence of events. A node in the prefix tree of all seen event
+     * sequences.
+     */
+    private class EventNode {
+        // Events that were seen just after this event.
+        private final Map<String, EventNode> mNextEvents = new HashMap<>();
+        // Whether we believe that further iterations will not be able to add more events to
+        // mNextEvents.
+        private boolean mStoppedAddingChildren = true;
+
+        private void debugDump(StringBuilder sb, int indent, String name) {
+            for (int i = 0; i < indent; ++i) sb.append('.');
+            sb.append(!mStoppedAddingChildren ? "+" : "-");
+            sb.append(" : ");
+            sb.append(name);
+            if (mLastRegisteredEvent == this) sb.append(" <");
+            sb.append('\n');
+
+            for (String key : mNextEvents.keySet()) {
+                mNextEvents.get(key).debugDump(sb, indent + 2, key);
+            }
+        }
+
+        /** Number of leaves in the subtree with this node as a root. */
+        private int numberOfLeafNodes() {
+            if (mNextEvents.isEmpty()) return 1;
+
+            int leaves = 0;
+            for (String event : mNextEvents.keySet()) {
+                leaves += mNextEvents.get(event).numberOfLeafNodes();
+            }
+            return leaves;
+        }
+
+        /**
+         * Whether we believe that further iterations will not be able add nodes to the subtree with
+         * this node as a root.
+         */
+        private boolean stoppedAddingChildrenToTree() {
+            if (!mStoppedAddingChildren) return false;
+
+            for (String event : mNextEvents.keySet()) {
+                if (!mNextEvents.get(event).stoppedAddingChildrenToTree()) return false;
+            }
+            return true;
+        }
+
+        /**
+         * In the subtree with this node as a root, tries finding a node where we may have a
+         * chance to add new children.
+         * If succeeds, returns true and fills 'path' with the sequence of events to that node;
+         * otherwise returns false.
+         */
+        private boolean populatePathToGrowthPoint(List<String> path) {
+            for (String event : mNextEvents.keySet()) {
+                if (mNextEvents.get(event).populatePathToGrowthPoint(path)) {
+                    path.add(0, event);
+                    return true;
+                }
+            }
+            if (!mStoppedAddingChildren) {
+                // Mark that we have finished adding children. It will remain true if no new
+                // children are added, or will be set to false upon adding a new child.
+                mStoppedAddingChildren = true;
+                return true;
+            }
+            return false;
+        }
+    }
+
+    // Starting point of all event sequences; the root of the prefix tree representation all
+    // sequences generated by test iterations. A test iteration can add nodes int it.
+    private EventNode mRoot = new EventNode();
+    // During a test iteration, the last event that was registered.
+    private EventNode mLastRegisteredEvent;
+    // Length of the current sequence of registered events for the current test iteration.
+    private int mRegisteredEventCount = 0;
+    // During the first part of a test iteration, we go to a specific node under mRoot by
+    // 'playing back' mSequenceToFollow. During this part, all events that don't belong to this
+    // sequence get postponed.
+    private List<String> mSequenceToFollow = new ArrayList<>();
+    // Collection of events that got postponed, with corresponding wait objects used to let them go.
+    private Map<String, Semaphore> mPostponedEvents = new HashMap<>();
+    // Callback to run by POSTPONED_EVENT_RESUME_HANDLER, used to let go of all currently
+    // postponed events.
+    private Runnable mResumeAllEventsCallback;
+    // String representation of the sequence of events registered so far for the current test
+    // iteration. After registering any event, we output it to the log. The last output before
+    // the test failure can be later played back to reliable reproduce the exact sequence of
+    // events that broke the test.
+    // Format: EV1|EV2|...\EVN
+    private StringBuilder mCurrentSequence;
+    // When not null, we are in a repro mode. We run only one test iteration, and are trying to
+    // reproduce the event sequence represented by this string. The format is same as for
+    // mCurrentSequence.
+    private final String mReproString;
+
+    /* Constructor for a normal test. */
+    public RaceConditionReproducer() {
+        mReproString = null;
+    }
+
+    /**
+     * Constructor for reliably reproducing a race condition failure. The developer should find in
+     * the log the latest "Repro sequence:" record and locally modify the test by passing that
+     * string to the constructor. Running the test will have only one iteration that will reliably
+     * "play back" that sequence.
+     */
+    public RaceConditionReproducer(String reproString) {
+        mReproString = reproString;
+    }
+
+    public RaceConditionReproducer(String... reproSequence) {
+        this(String.join("|", reproSequence));
+    }
+
+    public synchronized String getCurrentSequenceString() {
+        return mCurrentSequence.toString();
+    }
+
+    /**
+     * Starts a new test iteration. Events reported via RaceConditionTracker.onEvent before this
+     * call will be ignored.
+     */
+    public synchronized void startIteration() {
+        mLastRegisteredEvent = mRoot;
+        mRegisteredEventCount = 0;
+        mCurrentSequence = new StringBuilder();
+        Log.d(TAG, "Repro sequence: " + mCurrentSequence);
+        mSequenceToFollow = mReproString != null ?
+                parseReproString(mReproString) : generateSequenceToFollowLocked();
+        Log.e(TAG, "---- Start of iteration; state:\n" + dumpStateLocked());
+        checkIfCompletedSequenceToFollowLocked();
+
+        TraceHelperForTest.setRaceConditionReproducer(this);
+    }
+
+    /**
+     * Ends a new test iteration. Events reported via RaceConditionTracker.onEvent after this call
+     * will be ignored.
+     * Returns whether we need more iterations.
+     */
+    public synchronized boolean finishIteration() {
+        TraceHelperForTest.setRaceConditionReproducer(null);
+
+        runResumeAllEventsCallbackLocked();
+        assertTrue("Non-empty postponed events", mPostponedEvents.isEmpty());
+        assertTrue("Last registered event is :enter", lastEventAsEnter() == null);
+
+        // No events came after mLastRegisteredEvent. It doesn't make sense to come to it again
+        // because we won't see new continuations.
+        mLastRegisteredEvent.mStoppedAddingChildren = true;
+        Log.e(TAG, "---- End of iteration; state:\n" + dumpStateLocked());
+        if (mReproString != null) {
+            assertTrue("Repro mode: failed to reproduce the sequence",
+                    mCurrentSequence.toString().startsWith(mReproString));
+        }
+        // If we are in a repro mode, we need only one iteration. Otherwise, continue if the tree
+        // has prospective growth points.
+        return mReproString == null && !mRoot.stoppedAddingChildrenToTree();
+    }
+
+    private static List<String> parseReproString(String reproString) {
+        return Arrays.asList(reproString.split("\\|"));
+    }
+
+    /**
+     * Called when the app issues an event.
+     */
+    public void onEvent(String event) {
+        final Semaphore waitObject = tryRegisterEvent(event);
+        if (waitObject != null) {
+            waitUntilCanRegister(event, waitObject);
+        }
+    }
+
+    /**
+     * Returns whether the last event was not an XXX:enter, or this event is a matching XXX:exit.
+     */
+    private boolean canRegisterEventNowLocked(String event) {
+        final String lastEventAsEnter = lastEventAsEnter();
+        final String thisEventAsExit = eventAsExit(event);
+
+        if (lastEventAsEnter != null) {
+            if (!lastEventAsEnter.equals(thisEventAsExit)) {
+                assertTrue("YYY:exit after XXX:enter", thisEventAsExit == null);
+                // Last event was :enter, but this event is not :exit.
+                return false;
+            }
+        } else {
+            // Previous event was not :enter.
+            assertTrue(":exit after a non-enter event", thisEventAsExit == null);
+        }
+        return true;
+    }
+
+    /**
+     * Registers an event issued by the app and returns null or decides that the event must be
+     * postponed, and returns an object to wait on.
+     */
+    private synchronized Semaphore tryRegisterEvent(String event) {
+        Log.d(TAG, "Event issued by the app: " + event);
+
+        if (!canRegisterEventNowLocked(event)) {
+            return createWaitObjectForPostponedEventLocked(event);
+        }
+
+        if (mRegisteredEventCount < mSequenceToFollow.size()) {
+            // We are in the first part of the iteration. We only register events that follow the
+            // mSequenceToFollow and postponing all other events.
+            if (event.equals(mSequenceToFollow.get(mRegisteredEventCount))) {
+                // The event is the next one expected in the sequence. Register it.
+                registerEventLocked(event);
+
+                // If there are postponed events that could continue the sequence, register them.
+                while (mRegisteredEventCount < mSequenceToFollow.size() &&
+                        mPostponedEvents.containsKey(
+                                mSequenceToFollow.get(mRegisteredEventCount))) {
+                    registerPostponedEventLocked(mSequenceToFollow.get(mRegisteredEventCount));
+                }
+
+                // Perhaps we just completed the required sequence...
+                checkIfCompletedSequenceToFollowLocked();
+            } else {
+                // The event is not the next one in the sequence. Postpone it.
+                return createWaitObjectForPostponedEventLocked(event);
+            }
+        } else if (mRegisteredEventCount == mSequenceToFollow.size()) {
+            // The second phase of the iteration. We have just registered the whole
+            // mSequenceToFollow, and want to add previously not seen continuations for the last
+            // node in the sequence aka 'growth point'.
+            if (!mLastRegisteredEvent.mNextEvents.containsKey(event) || mReproString != null) {
+                // The event was never seen as a continuation for the current node.
+                // Or we are in repro mode, in which case we are not in business of generating
+                // new sequences after we've played back the required sequence.
+                // Register it immediately.
+                registerEventLocked(event);
+            } else {
+                // The event was seen as a continuation for the current node. Postpone it, hoping
+                // that a new event will come from other threads.
+                return createWaitObjectForPostponedEventLocked(event);
+            }
+        } else {
+            // The third phase of the iteration. We are past the growth point and register
+            // everything that comes.
+            registerEventLocked(event);
+            // Register events that may have been postponed while waiting for an :exit event
+            // during the third phase. We don't do this if just registered event is :enter.
+            if (eventAsEnter(event) == null && mRegisteredEventCount > mSequenceToFollow.size()) {
+                registerPostponedEventsLocked(new HashSet<>(mPostponedEvents.keySet()));
+            }
+        }
+        return null;
+    }
+
+    /** Called when there are chances that we just have registered the whole mSequenceToFollow. */
+    private void checkIfCompletedSequenceToFollowLocked() {
+        if (mRegisteredEventCount == mSequenceToFollow.size()) {
+            // We just entered the second phase of the iteration. We have just registered the
+            // whole mSequenceToFollow, and want to add previously not seen continuations for the
+            // last node in the sequence aka 'growth point'. All seen continuations will be
+            // postponed for SHORT_TIMEOUT_MS. At the end of this time period, we'll let them go.
+            scheduleResumeAllEventsLocked();
+
+            // Among the events that were postponed during the first stage, there may be an event
+            // that wasn't seen after the current. If so, register it immediately because this
+            // creates a new sequence.
+            final Set<String> keys = new HashSet<>(mPostponedEvents.keySet());
+            keys.removeAll(mLastRegisteredEvent.mNextEvents.keySet());
+            if (!keys.isEmpty()) {
+                registerPostponedEventLocked(keys.iterator().next());
+            }
+        }
+    }
+
+    private Semaphore createWaitObjectForPostponedEventLocked(String event) {
+        final Semaphore waitObject = new Semaphore(0);
+        assertTrue("Event already postponed: " + event, !mPostponedEvents.containsKey(event));
+        mPostponedEvents.put(event, waitObject);
+        return waitObject;
+    }
+
+    private void waitUntilCanRegister(String event, Semaphore waitObject) {
+        try {
+            assertTrue("Never registered event: " + event,
+                    waitObject.tryAcquire(LONG_TIMEOUT_MS, TimeUnit.MILLISECONDS));
+        } catch (InterruptedException e) {
+            fail("Wait was interrupted");
+        }
+    }
+
+    /** Schedules resuming all postponed events after SHORT_TIMEOUT_MS */
+    private void scheduleResumeAllEventsLocked() {
+        assertTrue(mResumeAllEventsCallback == null);
+        mResumeAllEventsCallback = this::allEventsResumeCallback;
+        POSTPONED_EVENT_RESUME_HANDLER.postDelayed(mResumeAllEventsCallback, SHORT_TIMEOUT_MS);
+    }
+
+    private synchronized void allEventsResumeCallback() {
+        assertTrue("In callback, but callback is not set", mResumeAllEventsCallback != null);
+        mResumeAllEventsCallback = null;
+        registerPostponedEventsLocked(new HashSet<>(mPostponedEvents.keySet()));
+    }
+
+    private void registerPostponedEventsLocked(Collection<String> events) {
+        for (String event : events) {
+            registerPostponedEventLocked(event);
+            if (eventAsEnter(event) != null) {
+                // Once :enter is registered, switch to waiting for :exit to come. Won't register
+                // other postponed events.
+                break;
+            }
+        }
+    }
+
+    private void registerPostponedEventLocked(String event) {
+        mPostponedEvents.remove(event).release();
+        registerEventLocked(event);
+    }
+
+    /**
+     * If the last registered event was XXX:enter, returns XXX, otherwise, null.
+     */
+    private String lastEventAsEnter() {
+        return eventAsEnter(mCurrentSequence.substring(mCurrentSequence.lastIndexOf("|") + 1));
+    }
+
+    /**
+     * If the event is XXX:postfix, returns XXX, otherwise, null.
+     */
+    private static String prefixFromPostfixedEvent(String event, String postfix) {
+        final int columnPos = event.indexOf(':');
+        if (columnPos != -1 && postfix.equals(event.substring(columnPos + 1))) {
+            return event.substring(0, columnPos);
+        }
+        return null;
+    }
+
+    /**
+     * If the event is XXX:enter, returns XXX, otherwise, null.
+     */
+    private static String eventAsEnter(String event) {
+        return prefixFromPostfixedEvent(event, ENTER_POSTFIX);
+    }
+
+    /**
+     * If the event is XXX:exit, returns XXX, otherwise, null.
+     */
+    private static String eventAsExit(String event) {
+        return prefixFromPostfixedEvent(event, EXIT_POSTFIX);
+    }
+
+    private void registerEventLocked(String event) {
+        assertTrue(canRegisterEventNowLocked(event));
+
+        Log.d(TAG, "Actually registering event: " + event);
+        EventNode next = mLastRegisteredEvent.mNextEvents.get(event);
+        if (next == null) {
+            // This event wasn't seen after mLastRegisteredEvent.
+            next = new EventNode();
+            mLastRegisteredEvent.mNextEvents.put(event, next);
+            // The fact that we've added a new event after the previous one means that the
+            // previous event is still a growth point, unless this event is :exit, which means
+            // that the previous event is :enter.
+            mLastRegisteredEvent.mStoppedAddingChildren = eventAsExit(event) != null;
+        }
+
+        mLastRegisteredEvent = next;
+        mRegisteredEventCount++;
+
+        if (mCurrentSequence.length() > 0) mCurrentSequence.append("|");
+        mCurrentSequence.append(event);
+        Log.d(TAG, "Repro sequence: " + mCurrentSequence);
+    }
+
+    private void runResumeAllEventsCallbackLocked() {
+        if (mResumeAllEventsCallback != null) {
+            POSTPONED_EVENT_RESUME_HANDLER.removeCallbacks(mResumeAllEventsCallback);
+            mResumeAllEventsCallback.run();
+        }
+    }
+
+    private CharSequence dumpStateLocked() {
+        StringBuilder sb = new StringBuilder();
+
+        sb.append("Sequence to follow: ");
+        for (String event : mSequenceToFollow) sb.append(" " + event);
+        sb.append(".\n");
+        sb.append("Registered event count: " + mRegisteredEventCount);
+
+        sb.append("\nPostponed events: ");
+        for (String event : mPostponedEvents.keySet()) sb.append(" " + event);
+        sb.append(".");
+
+        sb.append("\nNodes: \n");
+        mRoot.debugDump(sb, 0, "");
+        return sb;
+    }
+
+    public int numberOfLeafNodes() {
+        return mRoot.numberOfLeafNodes();
+    }
+
+    private List<String> generateSequenceToFollowLocked() {
+        ArrayList<String> sequence = new ArrayList<>();
+        mRoot.populatePathToGrowthPoint(sequence);
+        return sequence;
+    }
+}
diff --git a/tests/src/com/android/launcher3/util/RaceConditionReproducerTest.java b/tests/src/com/android/launcher3/util/RaceConditionReproducerTest.java
new file mode 100644
index 0000000..59f2173
--- /dev/null
+++ b/tests/src/com/android/launcher3/util/RaceConditionReproducerTest.java
@@ -0,0 +1,209 @@
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.launcher3.util;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import androidx.test.filters.LargeTest;
+import androidx.test.runner.AndroidJUnit4;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Ignore;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+@LargeTest
+@RunWith(AndroidJUnit4.class)
+public class RaceConditionReproducerTest {
+    private final static String SOME_VALID_SEQUENCE_3_3 = "B1|A1|A2|B2|A3|B3";
+
+    private static int factorial(int n) {
+        int res = 1;
+        for (int i = 2; i <= n; ++i) res *= i;
+        return res;
+    }
+
+    RaceConditionReproducer eventProcessor;
+
+    @Before
+    public void setup() {
+        eventProcessor = new RaceConditionReproducer();
+    }
+
+    @After
+    public void tearDown() {
+        TraceHelperForTest.cleanup();
+    }
+
+    private void run3_3_TestAction() throws InterruptedException {
+        Thread tb = new Thread(() -> {
+            eventProcessor.onEvent("B1");
+            eventProcessor.onEvent("B2");
+            eventProcessor.onEvent("B3");
+        });
+        tb.start();
+
+        eventProcessor.onEvent("A1");
+        eventProcessor.onEvent("A2");
+        eventProcessor.onEvent("A3");
+
+        tb.join();
+    }
+
+    @Test
+    @Ignore // The test is too long for continuous testing.
+    // 2 threads, 3 events each.
+    public void test3_3() throws Exception {
+        boolean sawTheValidSequence = false;
+
+        for (; ; ) {
+            eventProcessor.startIteration();
+            run3_3_TestAction();
+            final boolean needMoreIterations = eventProcessor.finishIteration();
+
+            sawTheValidSequence = sawTheValidSequence ||
+                    SOME_VALID_SEQUENCE_3_3.equals(eventProcessor.getCurrentSequenceString());
+
+            if (!needMoreIterations) break;
+        }
+
+        assertEquals("Wrong number of leaf nodes",
+                factorial(3 + 3) / (factorial(3) * factorial(3)),
+                eventProcessor.numberOfLeafNodes());
+        assertTrue(sawTheValidSequence);
+    }
+
+    @Test
+    @Ignore // The test is too long for continuous testing.
+    // 2 threads, 3 events, including enter-exit pairs each.
+    public void test3_3_enter_exit() throws Exception {
+        boolean sawTheValidSequence = false;
+
+        for (; ; ) {
+            eventProcessor.startIteration();
+            Thread tb = new Thread(() -> {
+                eventProcessor.onEvent("B1:enter");
+                eventProcessor.onEvent("B1:exit");
+                eventProcessor.onEvent("B2");
+                eventProcessor.onEvent("B3:enter");
+                eventProcessor.onEvent("B3:exit");
+            });
+            tb.start();
+
+            eventProcessor.onEvent("A1");
+            eventProcessor.onEvent("A2:enter");
+            eventProcessor.onEvent("A2:exit");
+            eventProcessor.onEvent("A3:enter");
+            eventProcessor.onEvent("A3:exit");
+
+            tb.join();
+            final boolean needMoreIterations = eventProcessor.finishIteration();
+
+            sawTheValidSequence = sawTheValidSequence ||
+                    "B1:enter|B1:exit|A1|A2:enter|A2:exit|B2|A3:enter|A3:exit|B3:enter|B3:exit".
+                            equals(eventProcessor.getCurrentSequenceString());
+
+            if (!needMoreIterations) break;
+        }
+
+        assertEquals("Wrong number of leaf nodes",
+                factorial(3 + 3) / (factorial(3) * factorial(3)),
+                eventProcessor.numberOfLeafNodes());
+        assertTrue(sawTheValidSequence);
+    }
+
+    @Test
+    // 2 threads, 3 events each; reproducing a particular event sequence.
+    public void test3_3_ReproMode() throws Exception {
+        eventProcessor = new RaceConditionReproducer(SOME_VALID_SEQUENCE_3_3);
+        eventProcessor.startIteration();
+        run3_3_TestAction();
+        assertTrue(!eventProcessor.finishIteration());
+        assertEquals(SOME_VALID_SEQUENCE_3_3, eventProcessor.getCurrentSequenceString());
+
+        assertEquals("Wrong number of leaf nodes", 1, eventProcessor.numberOfLeafNodes());
+    }
+
+    @Test
+    @Ignore // The test is too long for continuous testing.
+    // 2 threads with 2 events; 1 thread with 1 event.
+    public void test2_1_2() throws Exception {
+        for (; ; ) {
+            eventProcessor.startIteration();
+            Thread tb = new Thread(() -> {
+                eventProcessor.onEvent("B1");
+                eventProcessor.onEvent("B2");
+            });
+            tb.start();
+
+            Thread tc = new Thread(() -> {
+                eventProcessor.onEvent("C1");
+            });
+            tc.start();
+
+            eventProcessor.onEvent("A1");
+            eventProcessor.onEvent("A2");
+
+            tb.join();
+            tc.join();
+
+            if (!eventProcessor.finishIteration()) break;
+        }
+
+        assertEquals("Wrong number of leaf nodes",
+                factorial(2 + 2 + 1) / (factorial(2) * factorial(2) * factorial(1)),
+                eventProcessor.numberOfLeafNodes());
+    }
+
+    @Test
+    @Ignore // The test is too long for continuous testing.
+    // 2 threads with 2 events; 1 thread with 1 event. Includes enter-exit pairs.
+    public void test2_1_2_enter_exit() throws Exception {
+        for (; ; ) {
+            eventProcessor.startIteration();
+            Thread tb = new Thread(() -> {
+                eventProcessor.onEvent("B1:enter");
+                eventProcessor.onEvent("B1:exit");
+                eventProcessor.onEvent("B2:enter");
+                eventProcessor.onEvent("B2:exit");
+            });
+            tb.start();
+
+            Thread tc = new Thread(() -> {
+                eventProcessor.onEvent("C1:enter");
+                eventProcessor.onEvent("C1:exit");
+            });
+            tc.start();
+
+            eventProcessor.onEvent("A1:enter");
+            eventProcessor.onEvent("A1:exit");
+            eventProcessor.onEvent("A2:enter");
+            eventProcessor.onEvent("A2:exit");
+
+            tb.join();
+            tc.join();
+
+            if (!eventProcessor.finishIteration()) break;
+        }
+
+        assertEquals("Wrong number of leaf nodes",
+                factorial(2 + 2 + 1) / (factorial(2) * factorial(2) * factorial(1)),
+                eventProcessor.numberOfLeafNodes());
+    }
+}
diff --git a/tests/src/com/android/launcher3/util/TraceHelperForTest.java b/tests/src/com/android/launcher3/util/TraceHelperForTest.java
new file mode 100644
index 0000000..f1c8a67
--- /dev/null
+++ b/tests/src/com/android/launcher3/util/TraceHelperForTest.java
@@ -0,0 +1,116 @@
+/**
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.android.launcher3.util;
+
+import java.util.LinkedList;
+import java.util.function.IntConsumer;
+
+public class TraceHelperForTest extends TraceHelper {
+
+    private static final TraceHelperForTest INSTANCE_FOR_TEST = new TraceHelperForTest();
+
+    private final ThreadLocal<LinkedList<TraceInfo>> mStack =
+            ThreadLocal.withInitial(LinkedList::new);
+
+    private RaceConditionReproducer mRaceConditionReproducer;
+    private IntConsumer mFlagsChangeListener;
+
+    public static void setRaceConditionReproducer(RaceConditionReproducer reproducer) {
+        TraceHelper.INSTANCE = INSTANCE_FOR_TEST;
+        INSTANCE_FOR_TEST.mRaceConditionReproducer = reproducer;
+    }
+
+    public static void cleanup() {
+        INSTANCE_FOR_TEST.mRaceConditionReproducer = null;
+        INSTANCE_FOR_TEST.mFlagsChangeListener = null;
+    }
+
+    public static void setFlagsChangeListener(IntConsumer listener) {
+        TraceHelper.INSTANCE = INSTANCE_FOR_TEST;
+        INSTANCE_FOR_TEST.mFlagsChangeListener = listener;
+    }
+
+    private TraceHelperForTest() { }
+
+    @Override
+    public Object beginSection(String sectionName, int flags) {
+        LinkedList<TraceInfo> stack = mStack.get();
+        TraceInfo info = new TraceInfo(sectionName, flags);
+        stack.add(info);
+
+        if ((flags & TraceHelper.FLAG_CHECK_FOR_RACE_CONDITIONS) != 0
+                 && mRaceConditionReproducer != null) {
+            mRaceConditionReproducer.onEvent(RaceConditionReproducer.enterEvt(sectionName));
+        }
+        updateBinderTracking(stack);
+
+        super.beginSection(sectionName, flags);
+        return info;
+    }
+
+    @Override
+    public void endSection(Object token) {
+        LinkedList<TraceInfo> stack = mStack.get();
+        if (stack.size() == 0) {
+            new Throwable().printStackTrace();
+        }
+        TraceInfo info = (TraceInfo) token;
+        stack.remove(info);
+        if ((info.flags & TraceHelper.FLAG_CHECK_FOR_RACE_CONDITIONS) != 0
+                && mRaceConditionReproducer != null) {
+            mRaceConditionReproducer.onEvent(RaceConditionReproducer.exitEvt(info.sectionName));
+        }
+        updateBinderTracking(stack);
+
+        super.endSection(token);
+    }
+
+    @Override
+    public Object beginFlagsOverride(int flags) {
+        LinkedList<TraceInfo> stack = mStack.get();
+        TraceInfo info = new TraceInfo(null, flags);
+        stack.add(info);
+        updateBinderTracking(stack);
+        super.beginFlagsOverride(flags);
+        return info;
+    }
+
+    @Override
+    public void endFlagsOverride(Object token) {
+        super.endFlagsOverride(token);
+        LinkedList<TraceInfo> stack = mStack.get();
+        TraceInfo info = (TraceInfo) token;
+        stack.remove(info);
+        updateBinderTracking(stack);
+    }
+
+    private void updateBinderTracking(LinkedList<TraceInfo> stack) {
+        if (mFlagsChangeListener != null) {
+            mFlagsChangeListener.accept(stack.stream()
+                    .mapToInt(info -> info.flags).reduce(0, (a, b) -> a | b));
+        }
+    }
+
+    private static class TraceInfo {
+        public final String sectionName;
+        public final int flags;
+
+        TraceInfo(String sectionName, int flags) {
+            this.sectionName = sectionName;
+            this.flags = flags;
+        }
+    }
+}