Block posting new tasks until queue size is reduced

Also use LimitedTaskQueue instead of TaskQueueForTest in VideoAnalyzer. This prevents buffering too many decoded frames.

Bug: webrtc:42225151, b/337757868
Change-Id: I75a304c7e4c8569505e31efc6455ce09d49f5a43
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/353380
Commit-Queue: Sergey Silkin <ssilkin@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Auto-Submit: Sergey Silkin <ssilkin@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#42425}

test/video_codec_tester.cc

@@ -186,25 +186,34 @@ class Pacer {
   TimeDelta delay_;
 };
 
+// A task queue that limits its maximum size and guarantees FIFO execution of
+// the scheduled tasks.
 class LimitedTaskQueue {
  public:
-  // The codec tester reads frames from video source in the main thread.
-  // Encoding and decoding are done in separate threads. If encoding or
-  // decoding is slow, the reading may go far ahead and may buffer too many
-  // frames in memory. To prevent this we limit the encoding/decoding queue
-  // size. When the queue is full, the main thread and, hence, reading frames
-  // from video source is blocked until a previously posted encoding/decoding
-  // task starts.
+  // Frame reading, encoding and decoding are handled in separate threads. If
+  // encoding or decoding is slow, the frame reader may run far ahead, loading
+  // many large frames into memory. To prevent this, we limit the maximum size
+  // of the task queue. When this limit is reached, posting new tasks is blocked
+  // until the queue size is reduced by executing previous tasks.
   static constexpr int kMaxTaskQueueSize = 3;
 
   LimitedTaskQueue() : queue_size_(0) {}
 
-  void PostScheduledTask(absl::AnyInvocable<void() &&> task, Timestamp start) {
+  void PostScheduledTask(absl::AnyInvocable<void() &&> task,
+                         Timestamp scheduled) {
+    {
+      // Block posting new tasks until the queue size is reduced.
+      MutexLock lock(&mutex_);
+      while (queue_size_ >= kMaxTaskQueueSize) {
+        task_executed_.Wait(TimeDelta::Seconds(10));
+        task_executed_.Reset();
+      }
+    }
+
     ++queue_size_;
-    task_queue_.PostTask([this, task = std::move(task), start]() mutable {
-      // `TaskQueue` doesn't guarantee FIFO order of execution for delayed
-      // tasks.
-      int64_t wait_ms = (start - Timestamp::Millis(rtc::TimeMillis())).ms();
+    task_queue_.PostTask([this, task = std::move(task), scheduled]() mutable {
+      Timestamp now = Timestamp::Millis(rtc::TimeMillis());
+      int64_t wait_ms = (scheduled - now).ms();
       if (wait_ms > 0) {
         RTC_CHECK_LT(wait_ms, 10000) << "Too high wait_ms " << wait_ms;
         SleepMs(wait_ms);
@@ -213,16 +222,19 @@ class LimitedTaskQueue {
       --queue_size_;
       task_executed_.Set();
     });
+  }
 
-    task_executed_.Reset();
-    if (queue_size_ > kMaxTaskQueueSize) {
-      task_executed_.Wait(rtc::Event::kForever);
-      RTC_CHECK(queue_size_ <= kMaxTaskQueueSize);
-    }
+  void PostTask(absl::AnyInvocable<void() &&> task) {
+    Timestamp now = Timestamp::Millis(rtc::TimeMillis());
+    PostScheduledTask(std::move(task), now);
   }
 
   void PostTaskAndWait(absl::AnyInvocable<void() &&> task) {
-    PostScheduledTask(std::move(task), Timestamp::Millis(rtc::TimeMillis()));
+    PostTask(std::move(task));
+    WaitForPreviouslyPostedTasks();
+  }
+
+  void WaitForPreviouslyPostedTasks() {
     task_queue_.WaitForPreviouslyPostedTasks();
   }
 
@@ -230,6 +242,7 @@ class LimitedTaskQueue {
   TaskQueueForTest task_queue_;
   std::atomic_int queue_size_;
   rtc::Event task_executed_;
+  Mutex mutex_;
 };
 
 class TesterY4mWriter {
@@ -776,7 +789,7 @@ class VideoCodecAnalyzer : public VideoCodecTester::VideoCodecStats {
   }
 
   VideoSource* const video_source_;
-  TaskQueueForTest task_queue_;
+  LimitedTaskQueue task_queue_;
   // RTP timestamp -> spatial layer -> Frame
   std::map<uint32_t, std::map<int, Frame>> frames_;
   std::map<uint32_t, EncodingSettings> encoding_settings_;