Simplify concurrency in FrameProcessingTaskExecutor

This CL replaces concurrent collections and atomic primitives with a single
lock, this way the code is easier to reason about.

PiperOrigin-RevId: 496718057

library/effect/src/main/java/com/google/android/exoplayer2/effect/FrameProcessingTaskExecutor.java

@@ -17,24 +17,27 @@ package com.google.android.exoplayer2.effect;
 
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
 
+import androidx.annotation.GuardedBy;
+import androidx.annotation.Nullable;
 import com.google.android.exoplayer2.util.FrameProcessingException;
 import com.google.android.exoplayer2.util.FrameProcessor;
-import com.google.android.exoplayer2.util.GlUtil;
-import java.util.concurrent.ConcurrentLinkedQueue;
+import java.util.ArrayDeque;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Future;
 import java.util.concurrent.RejectedExecutionException;
-import java.util.concurrent.atomic.AtomicBoolean;
 
 /**
  * Wrapper around a single thread {@link ExecutorService} for executing {@link FrameProcessingTask}
  * instances.
  *
+ * <p>Public methods can be called from any thread.
+ *
  * <p>The wrapper handles calling {@link
  * FrameProcessor.Listener#onFrameProcessingError(FrameProcessingException)} for errors that occur
- * during these tasks. Errors are assumed to be non-recoverable, so the {@code
- * FrameProcessingTaskExecutor} should be released if an error occurs.
+ * during these tasks. The listener is invoked from the {@link ExecutorService}. Errors are assumed
+ * to be non-recoverable, so the {@code FrameProcessingTaskExecutor} should be released if an error
+ * occurs.
  *
  * <p>{@linkplain #submitWithHighPriority(FrameProcessingTask) High priority tasks} are always
  * executed before {@linkplain #submit(FrameProcessingTask) default priority tasks}. Tasks with
@@ -44,33 +47,43 @@ import java.util.concurrent.atomic.AtomicBoolean;
 
   private final ExecutorService singleThreadExecutorService;
   private final FrameProcessor.Listener listener;
-  private final ConcurrentLinkedQueue<Future<?>> futures;
-  private final ConcurrentLinkedQueue<FrameProcessingTask> highPriorityTasks;
-  private final AtomicBoolean shouldCancelTasks;
+  private final Object lock;
+
+  @GuardedBy("lock")
+  private final ArrayDeque<FrameProcessingTask> highPriorityTasks;
+
+  @GuardedBy("lock")
+  private boolean shouldCancelTasks;
 
   /** Creates a new instance. */
   public FrameProcessingTaskExecutor(
       ExecutorService singleThreadExecutorService, FrameProcessor.Listener listener) {
     this.singleThreadExecutorService = singleThreadExecutorService;
     this.listener = listener;
-
-    futures = new ConcurrentLinkedQueue<>();
-    highPriorityTasks = new ConcurrentLinkedQueue<>();
-    shouldCancelTasks = new AtomicBoolean();
+    lock = new Object();
+    highPriorityTasks = new ArrayDeque<>();
   }
 
   /**
    * Submits the given {@link FrameProcessingTask} to be executed after all pending tasks have
    * completed.
    */
+  @SuppressWarnings("FutureReturnValueIgnored")
   public void submit(FrameProcessingTask task) {
-    if (shouldCancelTasks.get()) {
-      return;
+    @Nullable RejectedExecutionException executionException = null;
+    synchronized (lock) {
+      if (shouldCancelTasks) {
+        return;
+      }
+      try {
+        wrapTaskAndSubmitToExecutorService(task, /* isReleaseTask= */ false);
+      } catch (RejectedExecutionException e) {
+        executionException = e;
+      }
     }
-    try {
-      futures.add(wrapTaskAndSubmitToExecutorService(task));
-    } catch (RejectedExecutionException e) {
-      handleException(e);
+
+    if (executionException != null) {
+      handleException(executionException);
     }
   }
 
@@ -82,10 +95,12 @@ import java.util.concurrent.atomic.AtomicBoolean;
    * high-priority and have not started executing will be executed after this task is complete.
    */
   public void submitWithHighPriority(FrameProcessingTask task) {
-    if (shouldCancelTasks.get()) {
-      return;
+    synchronized (lock) {
+      if (shouldCancelTasks) {
+        return;
+      }
+      highPriorityTasks.add(task);
     }
-    highPriorityTasks.add(task);
     // If the ExecutorService has non-started tasks, the first of these non-started tasks will run
     // the task passed to this method. Just in case there are no non-started tasks, submit another
     // task to run high-priority tasks.
@@ -102,9 +117,12 @@ import java.util.concurrent.atomic.AtomicBoolean;
    */
   public void release(FrameProcessingTask releaseTask, long releaseWaitTimeMs)
       throws InterruptedException {
-    shouldCancelTasks.getAndSet(true);
-    cancelNonStartedTasks();
-    Future<?> releaseFuture = wrapTaskAndSubmitToExecutorService(releaseTask);
+    synchronized (lock) {
+      shouldCancelTasks = true;
+      highPriorityTasks.clear();
+    }
+    Future<?> releaseFuture =
+        wrapTaskAndSubmitToExecutorService(releaseTask, /* isReleaseTask= */ true);
     singleThreadExecutorService.shutdown();
     try {
       if (!singleThreadExecutorService.awaitTermination(releaseWaitTimeMs, MILLISECONDS)) {
@@ -116,51 +134,44 @@ import java.util.concurrent.atomic.AtomicBoolean;
     }
   }
 
-  private Future<?> wrapTaskAndSubmitToExecutorService(FrameProcessingTask defaultPriorityTask) {
+  private Future<?> wrapTaskAndSubmitToExecutorService(
+      FrameProcessingTask defaultPriorityTask, boolean isReleaseTask) {
     return singleThreadExecutorService.submit(
         () -> {
           try {
-            while (!highPriorityTasks.isEmpty()) {
-              highPriorityTasks.remove().run();
+            synchronized (lock) {
+              if (shouldCancelTasks && !isReleaseTask) {
+                return;
+              }
+            }
+
+            @Nullable FrameProcessingTask nextHighPriorityTask;
+            while (true) {
+              synchronized (lock) {
+                // Lock only polling to prevent blocking the public method calls.
+                nextHighPriorityTask = highPriorityTasks.poll();
+              }
+              if (nextHighPriorityTask == null) {
+                break;
+              }
+              nextHighPriorityTask.run();
             }
             defaultPriorityTask.run();
-            removeFinishedFutures();
-          } catch (FrameProcessingException | GlUtil.GlException | RuntimeException e) {
+          } catch (Exception e) {
             handleException(e);
           }
         });
   }
 
-  private void cancelNonStartedTasks() {
-    while (!futures.isEmpty()) {
-      futures.remove().cancel(/* mayInterruptIfRunning= */ false);
-    }
-  }
-
   private void handleException(Exception exception) {
-    if (shouldCancelTasks.getAndSet(true)) {
-      // Ignore exception after cancelation as it can be caused by a previously reported exception
-      // that is the reason for the cancelation.
-      return;
-    }
-    listener.onFrameProcessingError(FrameProcessingException.from(exception));
-    cancelNonStartedTasks();
-  }
-
-  private void removeFinishedFutures() {
-    while (!futures.isEmpty()) {
-      if (!futures.element().isDone()) {
+    synchronized (lock) {
+      if (shouldCancelTasks) {
+        // Ignore exception after cancelation as it can be caused by a previously reported exception
+        // that is the reason for the cancelation.
         return;
       }
-      try {
-        futures.remove().get();
-      } catch (ExecutionException impossible) {
-        // All exceptions are already caught in wrapTaskAndSubmitToExecutorService.
-        handleException(new IllegalStateException("Unexpected error", impossible));
-      } catch (InterruptedException e) {
-        Thread.currentThread().interrupt();
-        handleException(e);
-      }
+      shouldCancelTasks = true;
     }
+    listener.onFrameProcessingError(FrameProcessingException.from(exception));
   }
 }