cc: Add image decode queue functionality to image manager.

cc/tiles/image_controller.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/tiles/image_controller.h"
 
+#include "base/bind.h"
+#include "base/task_scheduler/post_task.h"
+#include "base/task_scheduler/task_traits.h"
+#include "base/threading/thread_restrictions.h"
+#include "base/trace_event/trace_event.h"
+#include "cc/base/completion_event.h"
+#include "cc/tiles/tile_task_manager.h"
+
 namespace cc {
 
-ImageController::ImageController() = default;
-ImageController::~ImageController() = default;
+ImageController::ImageDecodeRequestId
+    ImageController::s_next_image_decode_queue_id_ = 1;
+
+ImageController::ImageController(
+    base::SequencedTaskRunner* origin_task_runner,
+    scoped_refptr<base::SequencedTaskRunner> worker_task_runner)
+    : origin_task_runner_(origin_task_runner),
+      worker_task_runner_(std::move(worker_task_runner)),
+      weak_ptr_factory_(this) {}
+
+ImageController::~ImageController() {
+  StopWorkerTasks();
+}
+
+void ImageController::ResumeWorkerTasks() {
+  if (!worker_task_runner_)
+    return;
+
+  base::AutoLock hold(lock_);
+  if (!image_decode_queue_.empty()) {
+    worker_task_runner_->PostTask(
+        FROM_HERE,
+        base::Bind(&ImageController::ProcessNextImageDecodeOnWorkerThread,
+                   base::Unretained(this)));
+  }
+}
+
+void ImageController::StopWorkerTasks() {
+  // We can't have worker threads without a cache_ or a worker_task_runner_, so
+  // terminate early.
+  if (!cache_ || !worker_task_runner_)
+    return;
+
+  // Abort all tasks that are currently scheduled to run (we'll wait for them to
+  // finish next).
+  {
+    base::AutoLock hold(lock_);
+    abort_tasks_ = true;
+  }
+
+  // Post a task that will simply signal a completion event to ensure that we
+  // "flush" any scheduled tasks (they will abort).
+  CompletionEvent completion_event;
+  worker_task_runner_->PostTask(
+      FROM_HERE, base::Bind(+[](CompletionEvent* event) { event->Signal(); },

[ericrk, 2017/01/09 21:07:27]

never seen the "+" thing before... the more you know :D

+                            base::Unretained(&completion_event)));
+  completion_event.Wait();
+
+  // Reset the abort flag so that new tasks can be scheduled.
+  {
+    base::AutoLock hold(lock_);
+    abort_tasks_ = false;
+  }
+
+  // Now that we flushed everything, if there was a task running and it
+  // finished, it would have posted a completion callback back to the compositor
+  // thread. We don't want that, so invalidate the weak ptrs again. Note that
+  // nothing can start running between wait and this invalidate, since it would
+  // only run on the current (compositor) thread.
+  weak_ptr_factory_.InvalidateWeakPtrs();
+
+  // Now, begin cleanup.
+
+  // Unlock all of the locked images (note that this vector would only be
+  // populated if we actually need to unref the image.
+  for (auto image_pair : requested_locked_images_)
+    cache_->UnrefImage(image_pair.second);
+  requested_locked_images_.clear();
+
+  // Now, complete the tasks that already ran but haven't completed. These would
+  // be posted in the run loop, but since we invalidated the weak ptrs, we need
+  // to run everything manually.
+  for (auto& request_to_complete : requests_needing_completion_) {
+    ImageDecodeRequestId id = request_to_complete.first;
+    ImageDecodeRequest& request = request_to_complete.second;
+
+    // The task (if one exists) would have run already, so we just need to
+    // complete it.
+    if (request.task)
+      request.task->DidComplete();
+
+    // Issue the callback, and unref the image immediately. This is so that any
+    // code waiting on the callback can proceed, although we're breaking the
+    // promise of having this image decoded. This is unfortunate, but it seems
+    // like the least complexity to process an image decode controller becoming
+    // nullptr.
+    request.callback.Run(id);
+    if (request.need_unref)
+      cache_->UnrefImage(request.draw_image);
+  }
+  requests_needing_completion_.clear();
+
+  // Finally, complete all of the tasks that never started running. This is
+  // similar to the |requests_needing_completion_|, but happens at a different
+  // stage in the pipeline.
+  for (auto& request_pair : image_decode_queue_) {
+    ImageDecodeRequestId id = request_pair.first;
+    ImageDecodeRequest& request = request_pair.second;
+
+    if (request.task) {
+      // This task may have run via a different request, so only cancel it if
+      // it's "new". That is, the same task could have been referenced by
+      // several different image deque requests for the same image.
+      if (request.task->state().IsNew())
+        request.task->state().DidCancel();
+      request.task->DidComplete();
+    }
+    // Run the callback and unref the image.
+    request.callback.Run(id);
+    cache_->UnrefImage(request.draw_image);
+  }
+  image_decode_queue_.clear();
+}
 
 void ImageController::SetImageDecodeCache(ImageDecodeCache* cache) {
   if (!cache) {
     SetPredecodeImages(std::vector<DrawImage>(),
                        ImageDecodeCache::TracingInfo());
+    StopWorkerTasks();
   }
   cache_ = cache;
+  if (cache_)

[ericrk, 2017/01/09 21:07:27]

From looking at QueueImageDecode, it appears we would crash if you called it
without a cache_, so you can only add to image_decode_queue_ when cache_ exists.

It seems like it's only ever safe to transition from !cache_ to cache_ or from
cache_ to !cache_, in which case we will never have tasks to resume here?

If we were to switch caches (from one pointer to another), it seems like
refcounts would get messed up?

[vmpstr, 2017/01/09 21:13:24]

This was a left over from an earlier approach I had, I'm gonna remove it here.
Thanks for catching it!

+    ResumeWorkerTasks();
 }
 
 void ImageController::GetTasksForImagesAndRef(
     std::vector<DrawImage>* images,
     std::vector<scoped_refptr<TileTask>>* tasks,
     const ImageDecodeCache::TracingInfo& tracing_info) {
   DCHECK(cache_);
   for (auto it = images->begin(); it != images->end();) {
     scoped_refptr<TileTask> task;
     bool need_to_unref_when_finished =
@@ skipping 21 matching lines @@
 std::vector<scoped_refptr<TileTask>> ImageController::SetPredecodeImages(
     std::vector<DrawImage> images,
     const ImageDecodeCache::TracingInfo& tracing_info) {
   std::vector<scoped_refptr<TileTask>> new_tasks;
   GetTasksForImagesAndRef(&images, &new_tasks, tracing_info);
   UnrefImages(predecode_locked_images_);
   predecode_locked_images_ = std::move(images);
   return new_tasks;
 }
 
+ImageController::ImageDecodeRequestId ImageController::QueueImageDecode(
+    sk_sp<const SkImage> image,
+    const ImageDecodedCallback& callback) {
+  // We must not receive any image requests if we have no worker.
+  CHECK(worker_task_runner_);
+
+  // Generate the next id.
+  ImageDecodeRequestId id = s_next_image_decode_queue_id_++;
+
+  DCHECK(image);
+  auto image_bounds = image->bounds();
+  DrawImage draw_image(std::move(image), image_bounds, kNone_SkFilterQuality,
+                       SkMatrix::I());
+
+  // Get the tasks for this decode.
+  scoped_refptr<TileTask> task;
+  bool need_unref =
+      cache_->GetOutOfRasterDecodeTaskForImageAndRef(draw_image, &task);
+  // If we don't need to unref this, we don't actually have a task.
+  DCHECK(need_unref || !task);
+
+  // Schedule the task and signal that there is more work.
+  base::AutoLock hold(lock_);
+  image_decode_queue_[id] =
+      ImageDecodeRequest(id, draw_image, callback, std::move(task), need_unref);
+
+  // If this is the only image decode request, schedule a task to run.
+  // Otherwise, the task will be scheduled in the previou task's completion.
+  if (image_decode_queue_.size() == 1) {
+    // Post a worker task.
+    worker_task_runner_->PostTask(
+        FROM_HERE,
+        base::Bind(&ImageController::ProcessNextImageDecodeOnWorkerThread,
+                   base::Unretained(this)));
+  }
+
+  return id;
+}
+
+void ImageController::UnlockImageDecode(ImageDecodeRequestId id) {
+  // If the image exists, ie we actually need to unlock it, then do so.
+  auto it = requested_locked_images_.find(id);
+  if (it == requested_locked_images_.end())
+    return;
+
+  UnrefImages({it->second});
+  requested_locked_images_.erase(it);
+}
+
+void ImageController::ProcessNextImageDecodeOnWorkerThread() {
+  TRACE_EVENT0("cc", "ImageController::ProcessNextImageDecodeOnWorkerThread");
+  ImageDecodeRequest decode;
+  {
+    base::AutoLock hold(lock_);
+
+    // If we don't have any work, abort.
+    if (image_decode_queue_.empty() || abort_tasks_)
+      return;
+
+    // Take the next request from the queue.
+    auto decode_it = image_decode_queue_.begin();
+    DCHECK(decode_it != image_decode_queue_.end());
+    decode = std::move(decode_it->second);
+    image_decode_queue_.erase(decode_it);
+
+    // Notify that the task will need completion. Note that there are two cases
+    // where we process this. First, we might complete this task as a response
+    // to the posted task below. Second, we might complete it in
+    // StopWorkerTasks(). In either case, the task would have already run
+    // (either post task happens after running, or the thread was already joined
+    // which means the task ran). This means that we can put the decode into
+    // |requests_needing_completion_| here before actually running the task.
+    requests_needing_completion_[decode.id] = decode;
+  }
+
+  // Run the task if we need to run it. If the task state isn't new, then
+  // there is another task that is responsible for finishing it and cleaning
+  // up (and it already ran); we just need to post a completion callback.
+  // Note that the other tasks's completion will also run first, since the
+  // requests are ordered. So, when we process this task's completion, we
+  // won't actually do anything with the task and simply issue the callback.
+  if (decode.task && decode.task->state().IsNew()) {
+    decode.task->state().DidSchedule();
+    decode.task->state().DidStart();
+    decode.task->RunOnWorkerThread();
+    decode.task->state().DidFinish();
+  }
+  origin_task_runner_->PostTask(
+      FROM_HERE, base::Bind(&ImageController::ImageDecodeCompleted,
+                            weak_ptr_factory_.GetWeakPtr(), decode.id));
+}
+
+void ImageController::ImageDecodeCompleted(ImageDecodeRequestId id) {
+  ImageDecodedCallback callback;
+  {
+    base::AutoLock hold(lock_);
+
+    auto request_it = requests_needing_completion_.find(id);
+    DCHECK(request_it != requests_needing_completion_.end());
+    id = request_it->first;
+    ImageDecodeRequest& request = request_it->second;
+
+    // If we need to unref this decode, then we have to put it into the locked
+    // images vector.
+    if (request.need_unref)
+      requested_locked_images_[id] = std::move(request.draw_image);
+
+    // If we have a task that isn't completed yet, we need to complete it.
+    if (request.task && !request.task->HasCompleted()) {
+      request.task->OnTaskCompleted();
+      request.task->DidComplete();
+    }
+    // Finally, save the callback so we can run it without the lock, and erase
+    // the request from |requests_needing_completion_|.
+    callback = std::move(request.callback);
+    requests_needing_completion_.erase(request_it);
+  }
+
+  // Post another task to run.
+  worker_task_runner_->PostTask(
+      FROM_HERE,
+      base::Bind(&ImageController::ProcessNextImageDecodeOnWorkerThread,
+                 base::Unretained(this)));
+
+  // Finally run the requested callback.
+  callback.Run(id);
+}
+
+ImageController::ImageDecodeRequest::ImageDecodeRequest() = default;
+ImageController::ImageDecodeRequest::ImageDecodeRequest(
+    ImageDecodeRequestId id,
+    const DrawImage& draw_image,
+    const ImageDecodedCallback& callback,
+    scoped_refptr<TileTask> task,
+    bool need_unref)
+    : id(id),
+      draw_image(draw_image),
+      callback(callback),
+      task(std::move(task)),
+      need_unref(need_unref) {}
+ImageController::ImageDecodeRequest::ImageDecodeRequest(
+    ImageDecodeRequest&& other) = default;
+ImageController::ImageDecodeRequest::ImageDecodeRequest(
+    const ImageDecodeRequest& other) = default;
+ImageController::ImageDecodeRequest::~ImageDecodeRequest() = default;
+
+ImageController::ImageDecodeRequest& ImageController::ImageDecodeRequest::
+operator=(ImageDecodeRequest&& other) = default;
+ImageController::ImageDecodeRequest& ImageController::ImageDecodeRequest::
+operator=(const ImageDecodeRequest& other) = default;
+
 }  // namespace cc