gecko-dev/image/IDecodingTask.cpp

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "IDecodingTask.h"

#include "gfxPrefs.h"
#include "nsThreadUtils.h"

#include "Decoder.h"
#include "DecodePool.h"
#include "RasterImage.h"
#include "SurfaceCache.h"

#include "mozilla/SystemGroup.h"

namespace mozilla {

using gfx::IntRect;

namespace image {

///////////////////////////////////////////////////////////////////////////////
// Helpers for sending notifications to the image associated with a decoder.
///////////////////////////////////////////////////////////////////////////////

void
IDecodingTask::EnsureHasEventTarget(NotNull<RasterImage*> aImage)
{
  if (!mEventTarget) {
    // We determine the event target as late as possible, at the first dispatch
    // time, because the observers bound to an imgRequest will affect it.
    // We cache it rather than query for the event target each time because the
    // event target can change. We don't want to risk events being executed in
    // a different order than they are dispatched, which can happen if we
    // selected scheduler groups which have no ordering guarantees relative to
    // each other (e.g. it moves from scheduler group A for doc group DA to
    // scheduler group B for doc group DB due to changing observers -- if we
    // dispatched the first event on A, and the second on B, we don't know which
    // will execute first.)
    RefPtr<ProgressTracker> tracker = aImage->GetProgressTracker();
    if (tracker) {
      mEventTarget = tracker->GetEventTarget();
    } else {
      mEventTarget = SystemGroup::EventTargetFor(TaskCategory::Other);
    }
  }
}

bool
IDecodingTask::IsOnEventTarget() const
{
  // This is essentially equivalent to NS_IsOnMainThread() because all of the
  // event targets are for the main thread (although perhaps with a different
  // label / scheduler group). The observers in ProgressTracker may have
  // different event targets from this, so this is just a best effort guess.
  bool current = false;
  mEventTarget->IsOnCurrentThread(&current);
  return current;
}

void
IDecodingTask::NotifyProgress(NotNull<RasterImage*> aImage,
                              NotNull<Decoder*> aDecoder)
{
  MOZ_ASSERT(aDecoder->HasProgress() && !aDecoder->IsMetadataDecode());
  EnsureHasEventTarget(aImage);

  // Capture the decoder's state. If we need to notify asynchronously, it's
  // important that we don't wait until the lambda actually runs to capture the
  // state that we're going to notify. That would both introduce data races on
  // the decoder's state and cause inconsistencies between the NotifyProgress()
  // calls we make off-main-thread and the notifications that RasterImage
  // actually receives, which would cause bugs.
  Progress progress = aDecoder->TakeProgress();
  IntRect invalidRect = aDecoder->TakeInvalidRect();
  Maybe<uint32_t> frameCount = aDecoder->TakeCompleteFrameCount();
  DecoderFlags decoderFlags = aDecoder->GetDecoderFlags();
  SurfaceFlags surfaceFlags = aDecoder->GetSurfaceFlags();

  // Synchronously notify if we can.
  if (IsOnEventTarget() && !(decoderFlags & DecoderFlags::ASYNC_NOTIFY)) {
    aImage->NotifyProgress(progress, invalidRect, frameCount,
                           decoderFlags, surfaceFlags);
    return;
  }

  // We're forced to notify asynchronously.
  NotNull<RefPtr<RasterImage>> image = aImage;
  mEventTarget->Dispatch(NS_NewRunnableFunction(
                           "IDecodingTask::NotifyProgress",
                           [=]() -> void {
    image->NotifyProgress(progress, invalidRect, frameCount,
                          decoderFlags, surfaceFlags);
  }), NS_DISPATCH_NORMAL);
}

void
IDecodingTask::NotifyDecodeComplete(NotNull<RasterImage*> aImage,
                                    NotNull<Decoder*> aDecoder)
{
  MOZ_ASSERT(aDecoder->HasError() || !aDecoder->InFrame(),
             "Decode complete in the middle of a frame?");
  EnsureHasEventTarget(aImage);

  // Capture the decoder's state.
  DecoderFinalStatus finalStatus = aDecoder->FinalStatus();
  ImageMetadata metadata = aDecoder->GetImageMetadata();
  DecoderTelemetry telemetry = aDecoder->Telemetry();
  Progress progress = aDecoder->TakeProgress();
  IntRect invalidRect = aDecoder->TakeInvalidRect();
  Maybe<uint32_t> frameCount = aDecoder->TakeCompleteFrameCount();
  DecoderFlags decoderFlags = aDecoder->GetDecoderFlags();
  SurfaceFlags surfaceFlags = aDecoder->GetSurfaceFlags();

  // Synchronously notify if we can.
  if (IsOnEventTarget() && !(decoderFlags & DecoderFlags::ASYNC_NOTIFY)) {
    aImage->NotifyDecodeComplete(finalStatus, metadata, telemetry, progress,
                                 invalidRect, frameCount, decoderFlags,
                                 surfaceFlags);
    return;
  }

  // We're forced to notify asynchronously.
  NotNull<RefPtr<RasterImage>> image = aImage;
  mEventTarget->Dispatch(NS_NewRunnableFunction(
                           "IDecodingTask::NotifyDecodeComplete",
                           [=]() -> void {
    image->NotifyDecodeComplete(finalStatus, metadata, telemetry, progress,
                                invalidRect, frameCount, decoderFlags,
                                surfaceFlags);
  }), NS_DISPATCH_NORMAL);
}


///////////////////////////////////////////////////////////////////////////////
// IDecodingTask implementation.
///////////////////////////////////////////////////////////////////////////////

void
IDecodingTask::Resume()
{
  DecodePool::Singleton()->AsyncRun(this);
}


///////////////////////////////////////////////////////////////////////////////
// MetadataDecodingTask implementation.
///////////////////////////////////////////////////////////////////////////////

MetadataDecodingTask::MetadataDecodingTask(NotNull<Decoder*> aDecoder)
  : mMutex("mozilla::image::MetadataDecodingTask")
  , mDecoder(aDecoder)
{
  MOZ_ASSERT(mDecoder->IsMetadataDecode(),
             "Use DecodingTask for non-metadata decodes");
}

void
MetadataDecodingTask::Run()
{
  MutexAutoLock lock(mMutex);

  LexerResult result = mDecoder->Decode(WrapNotNull(this));

  if (result.is<TerminalState>()) {
    NotifyDecodeComplete(mDecoder->GetImage(), mDecoder);
    return;  // We're done.
  }

  if (result == LexerResult(Yield::NEED_MORE_DATA)) {
    // We can't make any more progress right now. We also don't want to report
    // any progress, because it's important that metadata decode results are
    // delivered atomically. The decoder itself will ensure that we get
    // reenqueued when more data is available; just return for now.
    return;
  }

  MOZ_ASSERT_UNREACHABLE("Metadata decode yielded for an unexpected reason");
}


///////////////////////////////////////////////////////////////////////////////
// AnonymousDecodingTask implementation.
///////////////////////////////////////////////////////////////////////////////

AnonymousDecodingTask::AnonymousDecodingTask(NotNull<Decoder*> aDecoder)
  : mDecoder(aDecoder)
{ }

void
AnonymousDecodingTask::Run()
{
  while (true) {
    LexerResult result = mDecoder->Decode(WrapNotNull(this));

    if (result.is<TerminalState>()) {
      return;  // We're done.
    }

    if (result == LexerResult(Yield::NEED_MORE_DATA)) {
      // We can't make any more progress right now. Let the caller decide how to
      // handle it.
      return;
    }

    // Right now we don't do anything special for other kinds of yields, so just
    // keep working.
    MOZ_ASSERT(result.is<Yield>());
  }
}

} // namespace image
} // namespace mozilla