SF: Generalize thread safety guards

Replace the guards with a uniform syntax that can be reused with
annotations other than mStateLock and SF_MAIN_THREAD.

Bug: 182939859
Test: Build
Change-Id: I03e6fe5d465111a5882d2fc1c09fe1dc9660aa07
diff --git a/services/surfaceflinger/MutexUtils.h b/services/surfaceflinger/MutexUtils.h
new file mode 100644
index 0000000..f8be6f3
--- /dev/null
+++ b/services/surfaceflinger/MutexUtils.h
@@ -0,0 +1,53 @@
+/*
+ * Copyright 2022 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.
+ */
+
+#pragma once
+
+#include <log/log.h>
+#include <utils/Mutex.h>
+
+namespace android {
+
+struct SCOPED_CAPABILITY ConditionalLock {
+    ConditionalLock(Mutex& mutex, bool lock) ACQUIRE(mutex) : mutex(mutex), lock(lock) {
+        if (lock) mutex.lock();
+    }
+
+    ~ConditionalLock() RELEASE() {
+        if (lock) mutex.unlock();
+    }
+
+    Mutex& mutex;
+    const bool lock;
+};
+
+struct SCOPED_CAPABILITY TimedLock {
+    TimedLock(Mutex& mutex, nsecs_t timeout, const char* whence) ACQUIRE(mutex)
+          : mutex(mutex), status(mutex.timedLock(timeout)) {
+        ALOGE_IF(!locked(), "%s timed out locking: %s (%d)", whence, strerror(-status), status);
+    }
+
+    ~TimedLock() RELEASE() {
+        if (locked()) mutex.unlock();
+    }
+
+    bool locked() const { return status == NO_ERROR; }
+
+    Mutex& mutex;
+    const status_t status;
+};
+
+} // namespace android