Revert^2 "Use timerfd to improve the accuracy of query timing"

This reverts commit a481dc184fd75f5118578624b5c0ed8ec24cdf7b.

Reason for revert: Update this change to ensure proper closure of the timerfd object.

Change-Id: I14530ba77a39c77b4c7af6855ec77ba4907ab9f9
diff --git a/service-t/src/com/android/server/connectivity/mdns/MdnsFeatureFlags.java b/service-t/src/com/android/server/connectivity/mdns/MdnsFeatureFlags.java
index 2f3bdc5..1cf5e4d 100644
--- a/service-t/src/com/android/server/connectivity/mdns/MdnsFeatureFlags.java
+++ b/service-t/src/com/android/server/connectivity/mdns/MdnsFeatureFlags.java
@@ -95,6 +95,11 @@
             "nsd_cached_services_retention_time";
     public static final int DEFAULT_CACHED_SERVICES_RETENTION_TIME_MILLISECONDS = 10000;
 
+    /**
+     * A feature flag to control whether the accurate delay callback should be enabled.
+     */
+    public static final String NSD_ACCURATE_DELAY_CALLBACK = "nsd_accurate_delay_callback";
+
     // Flag for offload feature
     public final boolean mIsMdnsOffloadFeatureEnabled;
 
@@ -128,6 +133,9 @@
     // Retention Time for cached services
     public final long mCachedServicesRetentionTime;
 
+    // Flag for accurate delay callback
+    public final boolean mIsAccurateDelayCallbackEnabled;
+
     // Flag to use shorter (16 characters + .local) hostnames
     public final boolean mIsShortHostnamesEnabled;
 
@@ -231,6 +239,14 @@
     }
 
     /**
+     * Indicates whether {@link #NSD_ACCURATE_DELAY_CALLBACK} is enabled, including for testing.
+     */
+    public boolean isAccurateDelayCallbackEnabled() {
+        return mIsAccurateDelayCallbackEnabled
+                || isForceEnabledForTest(NSD_ACCURATE_DELAY_CALLBACK);
+    }
+
+    /**
      * The constructor for {@link MdnsFeatureFlags}.
      */
     public MdnsFeatureFlags(boolean isOffloadFeatureEnabled,
@@ -244,6 +260,7 @@
             boolean avoidAdvertisingEmptyTxtRecords,
             boolean isCachedServicesRemovalEnabled,
             long cachedServicesRetentionTime,
+            boolean isAccurateDelayCallbackEnabled,
             boolean isShortHostnamesEnabled,
             @Nullable FlagOverrideProvider overrideProvider) {
         mIsMdnsOffloadFeatureEnabled = isOffloadFeatureEnabled;
@@ -257,6 +274,7 @@
         mAvoidAdvertisingEmptyTxtRecords = avoidAdvertisingEmptyTxtRecords;
         mIsCachedServicesRemovalEnabled = isCachedServicesRemovalEnabled;
         mCachedServicesRetentionTime = cachedServicesRetentionTime;
+        mIsAccurateDelayCallbackEnabled = isAccurateDelayCallbackEnabled;
         mIsShortHostnamesEnabled = isShortHostnamesEnabled;
         mOverrideProvider = overrideProvider;
     }
@@ -281,6 +299,7 @@
         private boolean mAvoidAdvertisingEmptyTxtRecords;
         private boolean mIsCachedServicesRemovalEnabled;
         private long mCachedServicesRetentionTime;
+        private boolean mIsAccurateDelayCallbackEnabled;
         private boolean mIsShortHostnamesEnabled;
         private FlagOverrideProvider mOverrideProvider;
 
@@ -299,6 +318,7 @@
             mAvoidAdvertisingEmptyTxtRecords = true; // Default enabled.
             mIsCachedServicesRemovalEnabled = false;
             mCachedServicesRetentionTime = DEFAULT_CACHED_SERVICES_RETENTION_TIME_MILLISECONDS;
+            mIsAccurateDelayCallbackEnabled = false;
             mIsShortHostnamesEnabled = true; // Default enabled.
             mOverrideProvider = null;
         }
@@ -426,6 +446,16 @@
         }
 
         /**
+         * Set whether the accurate delay callback is enabled.
+         *
+         * @see #NSD_ACCURATE_DELAY_CALLBACK
+         */
+        public Builder setIsAccurateDelayCallbackEnabled(boolean isAccurateDelayCallbackEnabled) {
+            mIsAccurateDelayCallbackEnabled = isAccurateDelayCallbackEnabled;
+            return this;
+        }
+
+        /**
          * Set whether the short hostnames feature is enabled.
          *
          * @see #NSD_USE_SHORT_HOSTNAMES
@@ -450,6 +480,7 @@
                     mAvoidAdvertisingEmptyTxtRecords,
                     mIsCachedServicesRemovalEnabled,
                     mCachedServicesRetentionTime,
+                    mIsAccurateDelayCallbackEnabled,
                     mIsShortHostnamesEnabled,
                     mOverrideProvider);
         }
diff --git a/service-t/src/com/android/server/connectivity/mdns/MdnsServiceTypeClient.java b/service-t/src/com/android/server/connectivity/mdns/MdnsServiceTypeClient.java
index 8c86fb8..56d4b9a 100644
--- a/service-t/src/com/android/server/connectivity/mdns/MdnsServiceTypeClient.java
+++ b/service-t/src/com/android/server/connectivity/mdns/MdnsServiceTypeClient.java
@@ -20,6 +20,7 @@
 import static com.android.server.connectivity.mdns.MdnsSearchOptions.AGGRESSIVE_QUERY_MODE;
 import static com.android.server.connectivity.mdns.MdnsServiceCache.ServiceExpiredCallback;
 import static com.android.server.connectivity.mdns.MdnsServiceCache.findMatchedResponse;
+import static com.android.server.connectivity.mdns.MdnsQueryScheduler.ScheduledQueryTaskArgs;
 import static com.android.server.connectivity.mdns.util.MdnsUtils.Clock;
 import static com.android.server.connectivity.mdns.util.MdnsUtils.buildMdnsServiceInfoFromResponse;
 
@@ -36,6 +37,7 @@
 
 import com.android.net.module.util.CollectionUtils;
 import com.android.net.module.util.DnsUtils;
+import com.android.net.module.util.RealtimeScheduler;
 import com.android.net.module.util.SharedLog;
 import com.android.server.connectivity.mdns.util.MdnsUtils;
 
@@ -94,6 +96,9 @@
     private final boolean removeServiceAfterTtlExpires =
             MdnsConfigs.removeServiceAfterTtlExpires();
     private final Clock clock;
+    // Use RealtimeScheduler for query scheduling, which allows for more accurate sending of
+    // queries.
+    @Nullable private final RealtimeScheduler realtimeScheduler;
 
     @Nullable private MdnsSearchOptions searchOptions;
 
@@ -139,8 +144,7 @@
         public void handleMessage(Message msg) {
             switch (msg.what) {
                 case EVENT_START_QUERYTASK: {
-                    final MdnsQueryScheduler.ScheduledQueryTaskArgs taskArgs =
-                            (MdnsQueryScheduler.ScheduledQueryTaskArgs) msg.obj;
+                    final ScheduledQueryTaskArgs taskArgs = (ScheduledQueryTaskArgs) msg.obj;
                     // QueryTask should be run immediately after being created (not be scheduled in
                     // advance). Because the result of "makeResponsesForResolve" depends on answers
                     // that were received before it is called, so to take into account all answers
@@ -174,7 +178,7 @@
                     final long now = clock.elapsedRealtime();
                     lastSentTime = now;
                     final long minRemainingTtl = getMinRemainingTtl(now);
-                    MdnsQueryScheduler.ScheduledQueryTaskArgs args =
+                    final ScheduledQueryTaskArgs args =
                             mdnsQueryScheduler.scheduleNextRun(
                                     sentResult.taskArgs.config,
                                     minRemainingTtl,
@@ -189,10 +193,14 @@
                     sharedLog.log(String.format("Query sent with transactionId: %d. "
                                     + "Next run: sessionId: %d, in %d ms",
                             sentResult.transactionId, args.sessionId, timeToNextTaskMs));
-                    dependencies.sendMessageDelayed(
-                            handler,
-                            handler.obtainMessage(EVENT_START_QUERYTASK, args),
-                            timeToNextTaskMs);
+                    if (realtimeScheduler != null) {
+                        setDelayedTask(args, timeToNextTaskMs);
+                    } else {
+                        dependencies.sendMessageDelayed(
+                                handler,
+                                handler.obtainMessage(EVENT_START_QUERYTASK, args),
+                                timeToNextTaskMs);
+                    }
                     break;
                 }
                 default:
@@ -254,6 +262,14 @@
                 return List.of(new DatagramPacket(queryBuffer, 0, queryBuffer.length, address));
             }
         }
+
+        /**
+         * @see RealtimeScheduler
+         */
+        @Nullable
+        public RealtimeScheduler createRealtimeScheduler(@NonNull Handler handler) {
+            return new RealtimeScheduler(handler);
+        }
     }
 
     /**
@@ -301,6 +317,8 @@
         this.mdnsQueryScheduler = new MdnsQueryScheduler();
         this.cacheKey = new MdnsServiceCache.CacheKey(serviceType, socketKey);
         this.featureFlags = featureFlags;
+        this.realtimeScheduler = featureFlags.isAccurateDelayCallbackEnabled()
+                ? dependencies.createRealtimeScheduler(handler) : null;
     }
 
     /**
@@ -310,6 +328,9 @@
         removeScheduledTask();
         mdnsQueryScheduler.cancelScheduledRun();
         serviceCache.unregisterServiceExpiredCallback(cacheKey);
+        if (realtimeScheduler != null) {
+            realtimeScheduler.close();
+        }
     }
 
     private List<MdnsResponse> getExistingServices() {
@@ -317,6 +338,12 @@
                 ? serviceCache.getCachedServices(cacheKey) : Collections.emptyList();
     }
 
+    private void setDelayedTask(ScheduledQueryTaskArgs args, long timeToNextTaskMs) {
+        realtimeScheduler.removeDelayedMessage(EVENT_START_QUERYTASK);
+        realtimeScheduler.sendDelayedMessage(
+                handler.obtainMessage(EVENT_START_QUERYTASK, args), timeToNextTaskMs);
+    }
+
     /**
      * Registers {@code listener} for receiving discovery event of mDNS service instances, and
      * starts
@@ -363,7 +390,7 @@
         }
         final long minRemainingTtl = getMinRemainingTtl(now);
         if (hadReply) {
-            MdnsQueryScheduler.ScheduledQueryTaskArgs args =
+            final ScheduledQueryTaskArgs args =
                     mdnsQueryScheduler.scheduleNextRun(
                             taskConfig,
                             minRemainingTtl,
@@ -377,10 +404,14 @@
             final long timeToNextTaskMs = calculateTimeToNextTask(args, now);
             sharedLog.log(String.format("Schedule a query. Next run: sessionId: %d, in %d ms",
                     args.sessionId, timeToNextTaskMs));
-            dependencies.sendMessageDelayed(
-                    handler,
-                    handler.obtainMessage(EVENT_START_QUERYTASK, args),
-                    timeToNextTaskMs);
+            if (realtimeScheduler != null) {
+                setDelayedTask(args, timeToNextTaskMs);
+            } else {
+                dependencies.sendMessageDelayed(
+                        handler,
+                        handler.obtainMessage(EVENT_START_QUERYTASK, args),
+                        timeToNextTaskMs);
+            }
         } else {
             final List<MdnsResponse> servicesToResolve = makeResponsesForResolve(socketKey);
             final QueryTask queryTask = new QueryTask(
@@ -420,7 +451,11 @@
     }
 
     private void removeScheduledTask() {
-        dependencies.removeMessages(handler, EVENT_START_QUERYTASK);
+        if (realtimeScheduler != null) {
+            realtimeScheduler.removeDelayedMessage(EVENT_START_QUERYTASK);
+        } else {
+            dependencies.removeMessages(handler, EVENT_START_QUERYTASK);
+        }
         sharedLog.log("Remove EVENT_START_QUERYTASK"
                 + ", current session: " + currentSessionId);
         ++currentSessionId;
@@ -506,10 +541,13 @@
                 }
             }
         }
-        if (dependencies.hasMessages(handler, EVENT_START_QUERYTASK)) {
+        final boolean hasScheduledTask = realtimeScheduler != null
+                ? realtimeScheduler.hasDelayedMessage(EVENT_START_QUERYTASK)
+                : dependencies.hasMessages(handler, EVENT_START_QUERYTASK);
+        if (hasScheduledTask) {
             final long now = clock.elapsedRealtime();
             final long minRemainingTtl = getMinRemainingTtl(now);
-            MdnsQueryScheduler.ScheduledQueryTaskArgs args =
+            final ScheduledQueryTaskArgs args =
                     mdnsQueryScheduler.maybeRescheduleCurrentRun(now, minRemainingTtl,
                             lastSentTime, currentSessionId + 1,
                             searchOptions.numOfQueriesBeforeBackoff());
@@ -518,10 +556,14 @@
                 final long timeToNextTaskMs = calculateTimeToNextTask(args, now);
                 sharedLog.log(String.format("Reschedule a query. Next run: sessionId: %d, in %d ms",
                         args.sessionId, timeToNextTaskMs));
-                dependencies.sendMessageDelayed(
-                        handler,
-                        handler.obtainMessage(EVENT_START_QUERYTASK, args),
-                        timeToNextTaskMs);
+                if (realtimeScheduler != null) {
+                    setDelayedTask(args, timeToNextTaskMs);
+                } else {
+                    dependencies.sendMessageDelayed(
+                            handler,
+                            handler.obtainMessage(EVENT_START_QUERYTASK, args),
+                            timeToNextTaskMs);
+                }
             }
         }
     }
@@ -686,10 +728,10 @@
     private static class QuerySentArguments {
         private final int transactionId;
         private final List<String> subTypes = new ArrayList<>();
-        private final MdnsQueryScheduler.ScheduledQueryTaskArgs taskArgs;
+        private final ScheduledQueryTaskArgs taskArgs;
 
         QuerySentArguments(int transactionId, @NonNull List<String> subTypes,
-                @NonNull MdnsQueryScheduler.ScheduledQueryTaskArgs taskArgs) {
+                @NonNull ScheduledQueryTaskArgs taskArgs) {
             this.transactionId = transactionId;
             this.subTypes.addAll(subTypes);
             this.taskArgs = taskArgs;
@@ -698,14 +740,14 @@
 
     // A FutureTask that enqueues a single query, and schedule a new FutureTask for the next task.
     private class QueryTask implements Runnable {
-        private final MdnsQueryScheduler.ScheduledQueryTaskArgs taskArgs;
+        private final ScheduledQueryTaskArgs taskArgs;
         private final List<MdnsResponse> servicesToResolve = new ArrayList<>();
         private final List<String> subtypes = new ArrayList<>();
         private final boolean sendDiscoveryQueries;
         private final List<MdnsResponse> existingServices = new ArrayList<>();
         private final boolean onlyUseIpv6OnIpv6OnlyNetworks;
         private final SocketKey socketKey;
-        QueryTask(@NonNull MdnsQueryScheduler.ScheduledQueryTaskArgs taskArgs,
+        QueryTask(@NonNull ScheduledQueryTaskArgs taskArgs,
                 @NonNull Collection<MdnsResponse> servicesToResolve,
                 @NonNull Collection<String> subtypes, boolean sendDiscoveryQueries,
                 @NonNull Collection<MdnsResponse> existingServices,
@@ -771,7 +813,7 @@
         return minRemainingTtl == Long.MAX_VALUE ? 0 : minRemainingTtl;
     }
 
-    private static long calculateTimeToNextTask(MdnsQueryScheduler.ScheduledQueryTaskArgs args,
+    private static long calculateTimeToNextTask(ScheduledQueryTaskArgs args,
             long now) {
         return Math.max(args.timeToRun - now, 0);
     }
diff --git a/staticlibs/Android.bp b/staticlibs/Android.bp
index 0eab6e7..8034e57 100644
--- a/staticlibs/Android.bp
+++ b/staticlibs/Android.bp
@@ -438,7 +438,11 @@
     srcs: [
         "device/com/android/net/module/util/FdEventsReader.java",
         "device/com/android/net/module/util/HandlerUtils.java",
+        "device/com/android/net/module/util/JniUtil.java",
+        "device/com/android/net/module/util/RealtimeScheduler.java",
         "device/com/android/net/module/util/SharedLog.java",
+        "device/com/android/net/module/util/ServiceConnectivityJni.java",
+        "device/com/android/net/module/util/TimerFdUtils.java",
         "framework/com/android/net/module/util/ByteUtils.java",
         "framework/com/android/net/module/util/CollectionUtils.java",
         "framework/com/android/net/module/util/DnsUtils.java",
diff --git a/staticlibs/device/com/android/net/module/util/RealtimeScheduler.java b/staticlibs/device/com/android/net/module/util/RealtimeScheduler.java
index c8fdf72..2d95223 100644
--- a/staticlibs/device/com/android/net/module/util/RealtimeScheduler.java
+++ b/staticlibs/device/com/android/net/module/util/RealtimeScheduler.java
@@ -227,6 +227,13 @@
         return enqueueTask(new MessageTask(msg, SystemClock.elapsedRealtime() + delayMs), delayMs);
     }
 
+    private static boolean isMessageTask(Task task, int what) {
+        if (task instanceof MessageTask && ((MessageTask) task).mMessage.what == what) {
+            return true;
+        }
+        return false;
+    }
+
     /**
      * Remove a scheduled message.
      *
@@ -234,8 +241,24 @@
      */
     public void removeDelayedMessage(int what) {
         ensureRunningOnCorrectThread();
-        mTaskQueue.removeIf(task -> task instanceof MessageTask
-                && ((MessageTask) task).mMessage.what == what);
+        mTaskQueue.removeIf(task -> isMessageTask(task, what));
+    }
+
+    /**
+     * Check if there is a scheduled message.
+     *
+     * @param what the message to be checked
+     * @return true if there is a target message, false otherwise.
+     */
+    public boolean hasDelayedMessage(int what) {
+        ensureRunningOnCorrectThread();
+
+        for (Task task : mTaskQueue) {
+            if (isMessageTask(task, what)) {
+                return true;
+            }
+        }
+        return false;
     }
 
     /**
diff --git a/tests/unit/java/com/android/server/connectivity/mdns/MdnsServiceTypeClientTests.java b/tests/unit/java/com/android/server/connectivity/mdns/MdnsServiceTypeClientTests.java
index 67f9d9c..dad03e0 100644
--- a/tests/unit/java/com/android/server/connectivity/mdns/MdnsServiceTypeClientTests.java
+++ b/tests/unit/java/com/android/server/connectivity/mdns/MdnsServiceTypeClientTests.java
@@ -59,6 +59,7 @@
 import android.text.TextUtils;
 
 import com.android.net.module.util.CollectionUtils;
+import com.android.net.module.util.RealtimeScheduler;
 import com.android.net.module.util.SharedLog;
 import com.android.server.connectivity.mdns.MdnsServiceInfo.TextEntry;
 import com.android.server.connectivity.mdns.util.MdnsUtils;
@@ -127,6 +128,8 @@
     private SharedLog mockSharedLog;
     @Mock
     private MdnsServiceTypeClient.Dependencies mockDeps;
+    @Mock
+    private RealtimeScheduler mockRealtimeScheduler;
     @Captor
     private ArgumentCaptor<MdnsServiceInfo> serviceInfoCaptor;
 
@@ -145,6 +148,7 @@
     private Message delayMessage = null;
     private Handler realHandler = null;
     private MdnsFeatureFlags featureFlags = MdnsFeatureFlags.newBuilder().build();
+    private Message message = null;
 
     @Before
     @SuppressWarnings("DoNotMock")
@@ -244,10 +248,21 @@
             return true;
         }).when(mockDeps).sendMessage(any(Handler.class), any(Message.class));
 
-        client = makeMdnsServiceTypeClient();
+        doAnswer(inv -> {
+            realHandler = (Handler) inv.getArguments()[0];
+            return mockRealtimeScheduler;
+        }).when(mockDeps).createRealtimeScheduler(any(Handler.class));
+
+        doAnswer(inv -> {
+            message = (Message) inv.getArguments()[0];
+            latestDelayMs = (long) inv.getArguments()[1];
+            return null;
+        }).when(mockRealtimeScheduler).sendDelayedMessage(any(), anyLong());
+
+        client = makeMdnsServiceTypeClient(featureFlags);
     }
 
-    private MdnsServiceTypeClient makeMdnsServiceTypeClient() {
+    private MdnsServiceTypeClient makeMdnsServiceTypeClient(MdnsFeatureFlags featureFlags) {
         return new MdnsServiceTypeClient(SERVICE_TYPE, mockSocketClient, currentThreadExecutor,
                 mockDecoderClock, socketKey, mockSharedLog, thread.getLooper(), mockDeps,
                 serviceCache, featureFlags);
@@ -1926,9 +1941,7 @@
 
     @Test
     public void testSendQueryWithKnownAnswers() throws Exception {
-        client = new MdnsServiceTypeClient(SERVICE_TYPE, mockSocketClient, currentThreadExecutor,
-                mockDecoderClock, socketKey, mockSharedLog, thread.getLooper(), mockDeps,
-                serviceCache,
+        client = makeMdnsServiceTypeClient(
                 MdnsFeatureFlags.newBuilder().setIsQueryWithKnownAnswerEnabled(true).build());
 
         doCallRealMethod().when(mockDeps).getDatagramPacketsFromMdnsPacket(
@@ -1990,9 +2003,7 @@
 
     @Test
     public void testSendQueryWithSubTypeWithKnownAnswers() throws Exception {
-        client = new MdnsServiceTypeClient(SERVICE_TYPE, mockSocketClient, currentThreadExecutor,
-                mockDecoderClock, socketKey, mockSharedLog, thread.getLooper(), mockDeps,
-                serviceCache,
+        client = makeMdnsServiceTypeClient(
                 MdnsFeatureFlags.newBuilder().setIsQueryWithKnownAnswerEnabled(true).build());
 
         doCallRealMethod().when(mockDeps).getDatagramPacketsFromMdnsPacket(
@@ -2114,6 +2125,73 @@
         assertEquals(9680L, latestDelayMs);
     }
 
+    @Test
+    public void sendQueries_AccurateDelayCallback() {
+        client = makeMdnsServiceTypeClient(
+                MdnsFeatureFlags.newBuilder().setIsAccurateDelayCallbackEnabled(true).build());
+
+        final int numOfQueriesBeforeBackoff = 2;
+        final MdnsSearchOptions searchOptions = MdnsSearchOptions.newBuilder()
+                .addSubtype(SUBTYPE)
+                .setQueryMode(AGGRESSIVE_QUERY_MODE)
+                .setNumOfQueriesBeforeBackoff(numOfQueriesBeforeBackoff)
+                .build();
+        startSendAndReceive(mockListenerOne, searchOptions);
+        verify(mockRealtimeScheduler, times(1)).removeDelayedMessage(EVENT_START_QUERYTASK);
+
+        // Verify that the first query has been sent.
+        verifyAndSendQuery(0 /* index */, 0 /* timeInMs */, true /* expectsUnicastResponse */,
+                true /* multipleSocketDiscovery */, 1 /* scheduledCount */,
+                1 /* sendMessageCount */, true /* useAccurateDelayCallback */);
+
+        // Verify that the second query has been sent
+        verifyAndSendQuery(1 /* index */, 0 /* timeInMs */, false /* expectsUnicastResponse */,
+                true /* multipleSocketDiscovery */, 2 /* scheduledCount */,
+                2 /* sendMessageCount */, true /* useAccurateDelayCallback */);
+
+        // Verify that the third query has been sent
+        verifyAndSendQuery(2 /* index */, TIME_BETWEEN_RETRANSMISSION_QUERIES_IN_BURST_MS,
+                false /* expectsUnicastResponse */, true /* multipleSocketDiscovery */,
+                3 /* scheduledCount */, 3 /* sendMessageCount */,
+                true /* useAccurateDelayCallback */);
+
+        // In backoff mode, the current scheduled task will be canceled and reschedule if the
+        // 0.8 * smallestRemainingTtl is larger than time to next run.
+        long currentTime = TEST_TTL / 2 + TEST_ELAPSED_REALTIME;
+        doReturn(currentTime).when(mockDecoderClock).elapsedRealtime();
+        doReturn(true).when(mockRealtimeScheduler).hasDelayedMessage(EVENT_START_QUERYTASK);
+        processResponse(createResponse(
+                "service-instance-1", "192.0.2.123", 5353,
+                SERVICE_TYPE_LABELS,
+                Collections.emptyMap(), TEST_TTL), socketKey);
+        // Verify that the message removal occurred.
+        verify(mockRealtimeScheduler, times(6)).removeDelayedMessage(EVENT_START_QUERYTASK);
+        assertNotNull(message);
+        verifyAndSendQuery(3 /* index */, (long) (TEST_TTL / 2 * 0.8) /* timeInMs */,
+                true /* expectsUnicastResponse */, true /* multipleSocketDiscovery */,
+                5 /* scheduledCount */, 4 /* sendMessageCount */,
+                true /* useAccurateDelayCallback */);
+
+        // Stop sending packets.
+        stopSendAndReceive(mockListenerOne);
+        verify(mockRealtimeScheduler, times(8)).removeDelayedMessage(EVENT_START_QUERYTASK);
+    }
+
+    @Test
+    public void testTimerFdCloseProperly() {
+        client = makeMdnsServiceTypeClient(
+                MdnsFeatureFlags.newBuilder().setIsAccurateDelayCallbackEnabled(true).build());
+
+        // Start query
+        startSendAndReceive(mockListenerOne, MdnsSearchOptions.newBuilder().build());
+        verify(mockRealtimeScheduler, times(1)).removeDelayedMessage(EVENT_START_QUERYTASK);
+
+        // Stop query and verify the close() method has been called.
+        stopSendAndReceive(mockListenerOne);
+        verify(mockRealtimeScheduler, times(2)).removeDelayedMessage(EVENT_START_QUERYTASK);
+        verify(mockRealtimeScheduler).close();
+    }
+
     private static MdnsServiceInfo matchServiceName(String name) {
         return argThat(info -> info.getServiceInstanceName().equals(name));
     }
@@ -2127,9 +2205,22 @@
 
     private void verifyAndSendQuery(int index, long timeInMs, boolean expectsUnicastResponse,
             boolean multipleSocketDiscovery, int scheduledCount) {
-        // Dispatch the message
-        if (delayMessage != null && realHandler != null) {
-            dispatchMessage();
+        verifyAndSendQuery(index, timeInMs, expectsUnicastResponse,
+                multipleSocketDiscovery, scheduledCount, index + 1 /* sendMessageCount */,
+                false /* useAccurateDelayCallback */);
+    }
+
+    private void verifyAndSendQuery(int index, long timeInMs, boolean expectsUnicastResponse,
+            boolean multipleSocketDiscovery, int scheduledCount, int sendMessageCount,
+            boolean useAccurateDelayCallback) {
+        if (useAccurateDelayCallback && message != null && realHandler != null) {
+            runOnHandler(() -> realHandler.dispatchMessage(message));
+            message = null;
+        } else {
+            // Dispatch the message
+            if (delayMessage != null && realHandler != null) {
+                dispatchMessage();
+            }
         }
         assertEquals(timeInMs, latestDelayMs);
         currentThreadExecutor.getAndClearLastScheduledRunnable().run();
@@ -2152,11 +2243,16 @@
                         eq(socketKey), eq(false));
             }
         }
-        verify(mockDeps, times(index + 1))
+        verify(mockDeps, times(sendMessageCount))
                 .sendMessage(any(Handler.class), any(Message.class));
         // Verify the task has been scheduled.
-        verify(mockDeps, times(scheduledCount))
-                .sendMessageDelayed(any(Handler.class), any(Message.class), anyLong());
+        if (useAccurateDelayCallback) {
+            verify(mockRealtimeScheduler, times(scheduledCount))
+                    .sendDelayedMessage(any(), anyLong());
+        } else {
+            verify(mockDeps, times(scheduledCount))
+                    .sendMessageDelayed(any(Handler.class), any(Message.class), anyLong());
+        }
     }
 
     private static String[] getTestServiceName(String instanceName) {