gecko-dev/image/SourceBuffer.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 "SourceBuffer.h"

#include <algorithm>
#include <cmath>
#include <cstring>
#include "mozilla/Likely.h"
#include "MainThreadUtils.h"
#include "SurfaceCache.h"

using std::max;
using std::min;

namespace mozilla {
namespace image {

//////////////////////////////////////////////////////////////////////////////
// SourceBufferIterator implementation.
//////////////////////////////////////////////////////////////////////////////

SourceBufferIterator::~SourceBufferIterator()
{
  if (mOwner) {
    mOwner->OnIteratorRelease();
  }
}

SourceBufferIterator::State
SourceBufferIterator::AdvanceOrScheduleResume(IResumable* aConsumer)
{
  MOZ_ASSERT(mOwner);
  return mOwner->AdvanceIteratorOrScheduleResume(*this, aConsumer);
}

bool
SourceBufferIterator::RemainingBytesIsNoMoreThan(size_t aBytes) const
{
  MOZ_ASSERT(mOwner);
  return mOwner->RemainingBytesIsNoMoreThan(*this, aBytes);
}


//////////////////////////////////////////////////////////////////////////////
// SourceBuffer implementation.
//////////////////////////////////////////////////////////////////////////////

SourceBuffer::SourceBuffer()
  : mMutex("image::SourceBuffer")
  , mConsumerCount(0)
{ }

SourceBuffer::~SourceBuffer()
{
  MOZ_ASSERT(mConsumerCount == 0,
             "SourceBuffer destroyed with active consumers");
}

nsresult
SourceBuffer::AppendChunk(Maybe<Chunk>&& aChunk)
{
  mMutex.AssertCurrentThreadOwns();

#ifdef DEBUG
  if (mChunks.Length() > 0) {
    NS_WARNING("Appending an extra chunk for SourceBuffer");
  }
#endif

  if (MOZ_UNLIKELY(!aChunk)) {
    return NS_ERROR_OUT_OF_MEMORY;
  }

  if (MOZ_UNLIKELY(aChunk->AllocationFailed())) {
    return NS_ERROR_OUT_OF_MEMORY;
  }

  if (MOZ_UNLIKELY(!mChunks.AppendElement(Move(*aChunk), fallible))) {
    return NS_ERROR_OUT_OF_MEMORY;
  }

  return NS_OK;
}

Maybe<SourceBuffer::Chunk>
SourceBuffer::CreateChunk(size_t aCapacity, bool aRoundUp /* = true */)
{
  if (MOZ_UNLIKELY(aCapacity == 0)) {
    MOZ_ASSERT_UNREACHABLE("Appending a chunk of zero size?");
    return Nothing();
  }

  // Round up if requested.
  size_t finalCapacity = aRoundUp ? RoundedUpCapacity(aCapacity)
                                  : aCapacity;

  // Use the size of the SurfaceCache as an additional heuristic to avoid
  // allocating huge buffers. Generally images do not get smaller when decoded,
  // so if we could store the source data in the SurfaceCache, we assume that
  // there's no way we'll be able to store the decoded version.
  if (MOZ_UNLIKELY(!SurfaceCache::CanHold(finalCapacity))) {
    return Nothing();
  }

  return Some(Chunk(finalCapacity));
}

nsresult
SourceBuffer::Compact()
{
  mMutex.AssertCurrentThreadOwns();

  MOZ_ASSERT(mConsumerCount == 0, "Should have no consumers here");
  MOZ_ASSERT(mWaitingConsumers.Length() == 0, "Shouldn't have waiters");
  MOZ_ASSERT(mStatus, "Should be complete here");

  // Compact our waiting consumers list, since we're complete and no future
  // consumer will ever have to wait.
  mWaitingConsumers.Compact();

  // If we have no chunks, then there's nothing to compact.
  if (mChunks.Length() < 1) {
    return NS_OK;
  }

  // If we have one chunk, then we can compact if it has excess capacity.
  if (mChunks.Length() == 1 && mChunks[0].Length() == mChunks[0].Capacity()) {
    return NS_OK;
  }

  // We can compact our buffer. Determine the total length.
  size_t length = 0;
  for (uint32_t i = 0 ; i < mChunks.Length() ; ++i) {
    length += mChunks[i].Length();
  }

  Maybe<Chunk> newChunk = CreateChunk(length, /* aRoundUp = */ false);
  if (MOZ_UNLIKELY(!newChunk || newChunk->AllocationFailed())) {
    NS_WARNING("Failed to allocate chunk for SourceBuffer compacting - OOM?");
    return NS_OK;
  }

  // Copy our old chunks into the new chunk.
  for (uint32_t i = 0 ; i < mChunks.Length() ; ++i) {
    size_t offset = newChunk->Length();
    MOZ_ASSERT(offset < newChunk->Capacity());
    MOZ_ASSERT(offset + mChunks[i].Length() <= newChunk->Capacity());

    memcpy(newChunk->Data() + offset, mChunks[i].Data(), mChunks[i].Length());
    newChunk->AddLength(mChunks[i].Length());
  }

  MOZ_ASSERT(newChunk->Length() == newChunk->Capacity(),
             "Compacted chunk has slack space");

  // Replace the old chunks with the new, compact chunk.
  mChunks.Clear();
  if (MOZ_UNLIKELY(NS_FAILED(AppendChunk(Move(newChunk))))) {
    return HandleError(NS_ERROR_OUT_OF_MEMORY);
  }
  mChunks.Compact();

  return NS_OK;
}

/* static */ size_t
SourceBuffer::RoundedUpCapacity(size_t aCapacity)
{
  // Protect against overflow.
  if (MOZ_UNLIKELY(SIZE_MAX - aCapacity < MIN_CHUNK_CAPACITY)) {
    return aCapacity;
  }

  // Round up to the next multiple of MIN_CHUNK_CAPACITY (which should be the
  // size of a page).
  size_t roundedCapacity =
    (aCapacity + MIN_CHUNK_CAPACITY - 1) & ~(MIN_CHUNK_CAPACITY - 1);
  MOZ_ASSERT(roundedCapacity >= aCapacity, "Bad math?");
  MOZ_ASSERT(roundedCapacity - aCapacity < MIN_CHUNK_CAPACITY, "Bad math?");

  return roundedCapacity;
}

size_t
SourceBuffer::FibonacciCapacityWithMinimum(size_t aMinCapacity)
{
  mMutex.AssertCurrentThreadOwns();

  // We grow the source buffer using a Fibonacci growth rate.

  size_t length = mChunks.Length();

  if (length == 0) {
    return aMinCapacity;
  }

  if (length == 1) {
    return max(2 * mChunks[0].Capacity(), aMinCapacity);
  }

  return max(mChunks[length - 1].Capacity() + mChunks[length - 2].Capacity(),
             aMinCapacity);
}

void
SourceBuffer::AddWaitingConsumer(IResumable* aConsumer)
{
  mMutex.AssertCurrentThreadOwns();

  MOZ_ASSERT(!mStatus, "Waiting when we're complete?");

  if (MOZ_UNLIKELY(NS_IsMainThread())) {
    NS_WARNING("SourceBuffer consumer on the main thread needed to wait");
  }

  mWaitingConsumers.AppendElement(aConsumer);
}

void
SourceBuffer::ResumeWaitingConsumers()
{
  mMutex.AssertCurrentThreadOwns();

  if (mWaitingConsumers.Length() == 0) {
    return;
  }

  for (uint32_t i = 0 ; i < mWaitingConsumers.Length() ; ++i) {
    mWaitingConsumers[i]->Resume();
  }

  mWaitingConsumers.Clear();
}

nsresult
SourceBuffer::ExpectLength(size_t aExpectedLength)
{
  MOZ_ASSERT(aExpectedLength > 0, "Zero expected size?");

  MutexAutoLock lock(mMutex);

  if (MOZ_UNLIKELY(mStatus)) {
    MOZ_ASSERT_UNREACHABLE("ExpectLength after SourceBuffer is complete");
    return NS_OK;
  }

  if (MOZ_UNLIKELY(mChunks.Length() > 0)) {
    MOZ_ASSERT_UNREACHABLE("Duplicate or post-Append call to ExpectLength");
    return NS_OK;
  }

  if (MOZ_UNLIKELY(NS_FAILED(AppendChunk(CreateChunk(aExpectedLength))))) {
    return HandleError(NS_ERROR_OUT_OF_MEMORY);
  }

  return NS_OK;
}

nsresult
SourceBuffer::Append(const char* aData, size_t aLength)
{
  MOZ_ASSERT(aData, "Should have a buffer");
  MOZ_ASSERT(aLength > 0, "Writing a zero-sized chunk");

  size_t currentChunkCapacity = 0;
  size_t currentChunkLength = 0;
  char* currentChunkData = nullptr;
  size_t currentChunkRemaining = 0;
  size_t forCurrentChunk = 0;
  size_t forNextChunk = 0;
  size_t nextChunkCapacity = 0;

  {
    MutexAutoLock lock(mMutex);

    if (MOZ_UNLIKELY(mStatus)) {
      // This SourceBuffer is already complete; ignore further data.
      return NS_ERROR_FAILURE;
    }

    if (MOZ_UNLIKELY(mChunks.Length() == 0)) {
      if (MOZ_UNLIKELY(NS_FAILED(AppendChunk(CreateChunk(aLength))))) {
        return HandleError(NS_ERROR_OUT_OF_MEMORY);
      }
    }

    // Copy out the current chunk's information so we can release the lock.
    // Note that this wouldn't be safe if multiple producers were allowed!
    Chunk& currentChunk = mChunks.LastElement();
    currentChunkCapacity = currentChunk.Capacity();
    currentChunkLength = currentChunk.Length();
    currentChunkData = currentChunk.Data();

    // Partition this data between the current chunk and the next chunk.
    // (Because we always allocate a chunk big enough to fit everything passed
    // to Append, we'll never need more than those two chunks to store
    // everything.)
    currentChunkRemaining = currentChunkCapacity - currentChunkLength;
    forCurrentChunk = min(aLength, currentChunkRemaining);
    forNextChunk = aLength - forCurrentChunk;

    // If we'll need another chunk, determine what its capacity should be while
    // we still hold the lock.
    nextChunkCapacity = forNextChunk > 0
                      ? FibonacciCapacityWithMinimum(forNextChunk)
                      : 0;
  }

  // Write everything we can fit into the current chunk.
  MOZ_ASSERT(currentChunkLength + forCurrentChunk <= currentChunkCapacity);
  memcpy(currentChunkData + currentChunkLength, aData, forCurrentChunk);

  // If there's something left, create a new chunk and write it there.
  Maybe<Chunk> nextChunk;
  if (forNextChunk > 0) {
    MOZ_ASSERT(nextChunkCapacity >= forNextChunk, "Next chunk too small?");
    nextChunk = CreateChunk(nextChunkCapacity);
    if (MOZ_LIKELY(nextChunk && !nextChunk->AllocationFailed())) {
      memcpy(nextChunk->Data(), aData + forCurrentChunk, forNextChunk);
      nextChunk->AddLength(forNextChunk);
    }
  }

  // Update shared data structures.
  {
    MutexAutoLock lock(mMutex);

    // Update the length of the current chunk.
    Chunk& currentChunk = mChunks.LastElement();
    MOZ_ASSERT(currentChunk.Data() == currentChunkData, "Multiple producers?");
    MOZ_ASSERT(currentChunk.Length() == currentChunkLength,
               "Multiple producers?");

    currentChunk.AddLength(forCurrentChunk);

    // If we created a new chunk, add it to the series.
    if (forNextChunk > 0) {
      if (MOZ_UNLIKELY(!nextChunk)) {
        return HandleError(NS_ERROR_OUT_OF_MEMORY);
      }

      if (MOZ_UNLIKELY(NS_FAILED(AppendChunk(Move(nextChunk))))) {
        return HandleError(NS_ERROR_OUT_OF_MEMORY);
      }
    }

    // Resume any waiting readers now that there's new data.
    ResumeWaitingConsumers();
  }

  return NS_OK;
}

void
SourceBuffer::Complete(nsresult aStatus)
{
  MutexAutoLock lock(mMutex);

  if (MOZ_UNLIKELY(mStatus)) {
    MOZ_ASSERT_UNREACHABLE("Called Complete more than once");
    return;
  }

  if (MOZ_UNLIKELY(NS_SUCCEEDED(aStatus) && IsEmpty())) {
    // It's illegal to succeed without writing anything.
    aStatus = NS_ERROR_FAILURE;
  }

  mStatus = Some(aStatus);

  // Resume any waiting consumers now that we're complete.
  ResumeWaitingConsumers();

  // If we still have active consumers, just return.
  if (mConsumerCount > 0) {
    return;
  }

  // Attempt to compact our buffer down to a single chunk.
  Compact();
}

bool
SourceBuffer::IsComplete()
{
  MutexAutoLock lock(mMutex);
  return bool(mStatus);
}

size_t
SourceBuffer::SizeOfIncludingThisWithComputedFallback(MallocSizeOf
                                                        aMallocSizeOf) const
{
  MutexAutoLock lock(mMutex);

  size_t n = aMallocSizeOf(this);
  n += mChunks.SizeOfExcludingThis(aMallocSizeOf);

  for (uint32_t i = 0 ; i < mChunks.Length() ; ++i) {
    size_t chunkSize = aMallocSizeOf(mChunks[i].Data());

    if (chunkSize == 0) {
      // We're on a platform where moz_malloc_size_of always returns 0.
      chunkSize = mChunks[i].Capacity();
    }

    n += chunkSize;
  }

  return n;
}

SourceBufferIterator
SourceBuffer::Iterator()
{
  {
    MutexAutoLock lock(mMutex);
    mConsumerCount++;
  }

  return SourceBufferIterator(this);
}

void
SourceBuffer::OnIteratorRelease()
{
  MutexAutoLock lock(mMutex);

  MOZ_ASSERT(mConsumerCount > 0, "Consumer count doesn't add up");
  mConsumerCount--;

  // If we still have active consumers, or we're not complete yet, then return.
  if (mConsumerCount > 0 || !mStatus) {
    return;
  }

  // Attempt to compact our buffer down to a single chunk.
  Compact();
}

bool
SourceBuffer::RemainingBytesIsNoMoreThan(const SourceBufferIterator& aIterator,
                                         size_t aBytes) const
{
  MutexAutoLock lock(mMutex);

  // If we're not complete, we always say no.
  if (!mStatus) {
    return false;
  }

  // If the iterator's at the end, the answer is trivial.
  if (!aIterator.HasMore()) {
    return true;
  }

  uint32_t iteratorChunk = aIterator.mData.mIterating.mChunk;
  size_t iteratorOffset = aIterator.mData.mIterating.mOffset;
  size_t iteratorLength = aIterator.mData.mIterating.mLength;

  // Include the bytes the iterator is currently pointing to in the limit, so
  // that the current chunk doesn't have to be a special case.
  size_t bytes = aBytes + iteratorOffset + iteratorLength;

  // Count the length over all of our chunks, starting with the one that the
  // iterator is currently pointing to. (This is O(N), but N is expected to be
  // ~1, so it doesn't seem worth caching the length separately.)
  size_t lengthSoFar = 0;
  for (uint32_t i = iteratorChunk ; i < mChunks.Length() ; ++i) {
    lengthSoFar += mChunks[i].Length();
    if (lengthSoFar > bytes) {
      return false;
    }
  }

  return true;
}

SourceBufferIterator::State
SourceBuffer::AdvanceIteratorOrScheduleResume(SourceBufferIterator& aIterator,
                                              IResumable* aConsumer)
{
  MutexAutoLock lock(mMutex);

  if (MOZ_UNLIKELY(!aIterator.HasMore())) {
    MOZ_ASSERT_UNREACHABLE("Should not advance a completed iterator");
    return SourceBufferIterator::COMPLETE;
  }

  if (MOZ_UNLIKELY(mStatus && NS_FAILED(*mStatus))) {
    // This SourceBuffer is complete due to an error; all reads fail.
    return aIterator.SetComplete(*mStatus);
  }

  if (MOZ_UNLIKELY(mChunks.Length() == 0)) {
    // We haven't gotten an initial chunk yet.
    AddWaitingConsumer(aConsumer);
    return aIterator.SetWaiting();
  }

  uint32_t iteratorChunkIdx = aIterator.mData.mIterating.mChunk;
  MOZ_ASSERT(iteratorChunkIdx < mChunks.Length());

  const Chunk& currentChunk = mChunks[iteratorChunkIdx];
  size_t iteratorEnd = aIterator.mData.mIterating.mOffset +
                       aIterator.mData.mIterating.mLength;
  MOZ_ASSERT(iteratorEnd <= currentChunk.Length());
  MOZ_ASSERT(iteratorEnd <= currentChunk.Capacity());

  if (iteratorEnd < currentChunk.Length()) {
    // There's more data in the current chunk.
    return aIterator.SetReady(iteratorChunkIdx, currentChunk.Data(),
                              iteratorEnd, currentChunk.Length() - iteratorEnd);
  }

  if (iteratorEnd == currentChunk.Capacity() &&
      !IsLastChunk(iteratorChunkIdx)) {
    // Advance to the next chunk.
    const Chunk& nextChunk = mChunks[iteratorChunkIdx + 1];
    return aIterator.SetReady(iteratorChunkIdx + 1, nextChunk.Data(), 0,
                              nextChunk.Length());
  }

  MOZ_ASSERT(IsLastChunk(iteratorChunkIdx), "Should've advanced");

  if (mStatus) {
    // There's no more data and this SourceBuffer completed successfully.
    MOZ_ASSERT(NS_SUCCEEDED(*mStatus), "Handled failures earlier");
    return aIterator.SetComplete(*mStatus);
  }

  // We're not complete, but there's no more data right now. Arrange to wake up
  // the consumer when we get more data.
  AddWaitingConsumer(aConsumer);
  return aIterator.SetWaiting();
}

nsresult
SourceBuffer::HandleError(nsresult aError)
{
  MOZ_ASSERT(NS_FAILED(aError), "Should have an error here");
  MOZ_ASSERT(aError == NS_ERROR_OUT_OF_MEMORY,
             "Unexpected error; may want to notify waiting readers, which "
             "HandleError currently doesn't do");

  mMutex.AssertCurrentThreadOwns();

  NS_WARNING("SourceBuffer encountered an unrecoverable error");

  // Record the error.
  mStatus = Some(aError);

  // Drop our references to waiting readers.
  mWaitingConsumers.Clear();

  return *mStatus;
}

bool
SourceBuffer::IsEmpty()
{
  mMutex.AssertCurrentThreadOwns();
  return mChunks.Length() == 0 ||
         mChunks[0].Length() == 0;
}

bool
SourceBuffer::IsLastChunk(uint32_t aChunk)
{
  mMutex.AssertCurrentThreadOwns();
  return aChunk + 1 == mChunks.Length();
}

} // namespace image
} // namespace mozilla