gecko-dev/image/SourceBuffer.h

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/* -*- 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/. */
/**
* SourceBuffer is a single producer, multiple consumer data structure used for
* storing image source (compressed) data.
*/
#ifndef mozilla_image_sourcebuffer_h
#define mozilla_image_sourcebuffer_h
#include "mozilla/Maybe.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/Mutex.h"
#include "mozilla/Move.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/RefPtr.h"
#include "mozilla/RefCounted.h"
#include "mozilla/UniquePtr.h"
#include "mozilla/RefPtr.h"
#include "nsTArray.h"
class nsIInputStream;
namespace mozilla {
namespace image {
class SourceBuffer;
/**
* IResumable is an interface for classes that can schedule themselves to resume
* their work later. An implementation of IResumable generally should post a
* runnable to some event target which continues the work of the task.
*/
struct IResumable
{
MOZ_DECLARE_REFCOUNTED_TYPENAME(IResumable)
// Subclasses may or may not be XPCOM classes, so we just require that they
// implement AddRef and Release.
NS_IMETHOD_(MozExternalRefCountType) AddRef(void) = 0;
NS_IMETHOD_(MozExternalRefCountType) Release(void) = 0;
virtual void Resume() = 0;
protected:
virtual ~IResumable() { }
};
/**
* SourceBufferIterator is a class that allows consumers of image source data to
* read the contents of a SourceBuffer sequentially.
*
* Consumers can advance through the SourceBuffer by calling
* AdvanceOrScheduleResume() repeatedly. After every advance, they should call
* check the return value, which will tell them the iterator's new state.
*
* If WAITING is returned, AdvanceOrScheduleResume() has arranged
* to call the consumer's Resume() method later, so the consumer should save its
* state if needed and stop running.
*
* If the iterator's new state is READY, then the consumer can call Data() and
* Length() to read new data from the SourceBuffer.
*
* Finally, in the COMPLETE state the consumer can call CompletionStatus() to
* get the status passed to SourceBuffer::Complete().
*/
class SourceBufferIterator final
{
public:
enum State {
START, // The iterator is at the beginning of the buffer.
READY, // The iterator is pointing to new data.
WAITING, // The iterator is blocked and the caller must yield.
COMPLETE // The iterator is pointing to the end of the buffer.
};
explicit SourceBufferIterator(SourceBuffer* aOwner)
: mOwner(aOwner)
, mState(START)
{
MOZ_ASSERT(aOwner);
mData.mIterating.mChunk = 0;
mData.mIterating.mData = nullptr;
mData.mIterating.mOffset = 0;
mData.mIterating.mLength = 0;
}
SourceBufferIterator(SourceBufferIterator&& aOther)
: mOwner(Move(aOther.mOwner))
, mState(aOther.mState)
, mData(aOther.mData)
{ }
~SourceBufferIterator();
SourceBufferIterator& operator=(SourceBufferIterator&& aOther)
{
mOwner = Move(aOther.mOwner);
mState = aOther.mState;
mData = aOther.mData;
return *this;
}
/**
* Returns true if there are no more than @aBytes remaining in the
* SourceBuffer. If the SourceBuffer is not yet complete, returns false.
*/
bool RemainingBytesIsNoMoreThan(size_t aBytes) const;
/**
* Advances the iterator through the SourceBuffer if possible. If not,
* arranges to call the @aConsumer's Resume() method when more data is
* available.
*/
State AdvanceOrScheduleResume(IResumable* aConsumer);
/// If at the end, returns the status passed to SourceBuffer::Complete().
nsresult CompletionStatus() const
{
MOZ_ASSERT(mState == COMPLETE,
"Calling CompletionStatus() in the wrong state");
return mState == COMPLETE ? mData.mAtEnd.mStatus : NS_OK;
}
/// If we're ready to read, returns a pointer to the new data.
const char* Data() const
{
MOZ_ASSERT(mState == READY, "Calling Data() in the wrong state");
return mState == READY ? mData.mIterating.mData + mData.mIterating.mOffset
: nullptr;
}
/// If we're ready to read, returns the length of the new data.
size_t Length() const
{
MOZ_ASSERT(mState == READY, "Calling Length() in the wrong state");
return mState == READY ? mData.mIterating.mLength : 0;
}
private:
friend class SourceBuffer;
SourceBufferIterator(const SourceBufferIterator&) = delete;
SourceBufferIterator& operator=(const SourceBufferIterator&) = delete;
bool HasMore() const { return mState != COMPLETE; }
State SetReady(uint32_t aChunk, const char* aData,
size_t aOffset, size_t aLength)
{
MOZ_ASSERT(mState != COMPLETE);
mData.mIterating.mChunk = aChunk;
mData.mIterating.mData = aData;
mData.mIterating.mOffset = aOffset;
mData.mIterating.mLength = aLength;
return mState = READY;
}
State SetWaiting()
{
MOZ_ASSERT(mState != COMPLETE);
MOZ_ASSERT(mState != WAITING, "Did we get a spurious wakeup somehow?");
return mState = WAITING;
}
State SetComplete(nsresult aStatus)
{
mData.mAtEnd.mStatus = aStatus;
return mState = COMPLETE;
}
RefPtr<SourceBuffer> mOwner;
State mState;
/**
* This union contains our iteration state if we're still iterating (for
* states START, READY, and WAITING) and the status the SourceBuffer was
* completed with if we're in state COMPLETE.
*/
union {
struct {
uint32_t mChunk;
const char* mData;
size_t mOffset;
size_t mLength;
} mIterating;
struct {
nsresult mStatus;
} mAtEnd;
} mData;
};
/**
* SourceBuffer is a parallel data structure used for storing image source
* (compressed) data.
*
* SourceBuffer is a single producer, multiple consumer data structure. The
* single producer calls Append() to append data to the buffer. In parallel,
* multiple consumers can call Iterator(), which returns a SourceBufferIterator
* that they can use to iterate through the buffer. The SourceBufferIterator
* returns a series of pointers which remain stable for lifetime of the
* SourceBuffer, and the data they point to is immutable, ensuring that the
* producer never interferes with the consumers.
*
* In order to avoid blocking, SourceBuffer works with SourceBufferIterator to
* keep a list of consumers which are waiting for new data, and to resume them
* when the producer appends more. All consumers must implement the IResumable
* interface to make this possible.
*/
class SourceBuffer final
{
public:
MOZ_DECLARE_REFCOUNTED_TYPENAME(image::SourceBuffer)
NS_INLINE_DECL_THREADSAFE_REFCOUNTING(image::SourceBuffer)
SourceBuffer();
//////////////////////////////////////////////////////////////////////////////
// Producer methods.
//////////////////////////////////////////////////////////////////////////////
/**
* If the producer knows how long the source data will be, it should call
* ExpectLength, which enables SourceBuffer to preallocate its buffer.
*/
nsresult ExpectLength(size_t aExpectedLength);
/// Append the provided data to the buffer.
nsresult Append(const char* aData, size_t aLength);
/// Append the data available on the provided nsIInputStream to the buffer.
nsresult AppendFromInputStream(nsIInputStream* aInputStream, uint32_t aCount);
/**
* Mark the buffer complete, with a status that will be available to
* consumers. Further calls to Append() are forbidden after Complete().
*/
void Complete(nsresult aStatus);
/// Returns true if the buffer is complete.
bool IsComplete();
/// Memory reporting.
size_t SizeOfIncludingThisWithComputedFallback(MallocSizeOf) const;
//////////////////////////////////////////////////////////////////////////////
// Consumer methods.
//////////////////////////////////////////////////////////////////////////////
/// Returns an iterator to this SourceBuffer.
SourceBufferIterator Iterator();
private:
friend class SourceBufferIterator;
~SourceBuffer();
//////////////////////////////////////////////////////////////////////////////
// Chunk type and chunk-related methods.
//////////////////////////////////////////////////////////////////////////////
class Chunk
{
public:
explicit Chunk(size_t aCapacity)
: mCapacity(aCapacity)
, mLength(0)
{
MOZ_ASSERT(aCapacity > 0, "Creating zero-capacity chunk");
mData = new (fallible) char[mCapacity];
}
~Chunk() { delete[] mData; }
Chunk(Chunk&& aOther)
: mCapacity(aOther.mCapacity)
, mLength(aOther.mLength)
, mData(aOther.mData)
{
aOther.mCapacity = aOther.mLength = 0;
aOther.mData = nullptr;
}
Chunk& operator=(Chunk&& aOther)
{
mCapacity = aOther.mCapacity;
mLength = aOther.mLength;
mData = aOther.mData;
aOther.mCapacity = aOther.mLength = 0;
aOther.mData = nullptr;
return *this;
}
bool AllocationFailed() const { return !mData; }
size_t Capacity() const { return mCapacity; }
size_t Length() const { return mLength; }
char* Data() const
{
MOZ_ASSERT(mData, "Allocation failed but nobody checked for it");
return mData;
}
void AddLength(size_t aAdditionalLength)
{
MOZ_ASSERT(mLength + aAdditionalLength <= mCapacity);
mLength += aAdditionalLength;
}
private:
Chunk(const Chunk&) = delete;
Chunk& operator=(const Chunk&) = delete;
size_t mCapacity;
size_t mLength;
char* mData;
};
nsresult AppendChunk(Maybe<Chunk>&& aChunk);
Maybe<Chunk> CreateChunk(size_t aCapacity, bool aRoundUp = true);
nsresult Compact();
static size_t RoundedUpCapacity(size_t aCapacity);
size_t FibonacciCapacityWithMinimum(size_t aMinCapacity);
//////////////////////////////////////////////////////////////////////////////
// Iterator / consumer methods.
//////////////////////////////////////////////////////////////////////////////
void AddWaitingConsumer(IResumable* aConsumer);
void ResumeWaitingConsumers();
typedef SourceBufferIterator::State State;
State AdvanceIteratorOrScheduleResume(SourceBufferIterator& aIterator,
IResumable* aConsumer);
bool RemainingBytesIsNoMoreThan(const SourceBufferIterator& aIterator,
size_t aBytes) const;
void OnIteratorRelease();
//////////////////////////////////////////////////////////////////////////////
// Helper methods.
//////////////////////////////////////////////////////////////////////////////
nsresult HandleError(nsresult aError);
bool IsEmpty();
bool IsLastChunk(uint32_t aChunk);
//////////////////////////////////////////////////////////////////////////////
// Member variables.
//////////////////////////////////////////////////////////////////////////////
static const size_t MIN_CHUNK_CAPACITY = 4096;
/// All private members are protected by mMutex.
mutable Mutex mMutex;
/// The data in this SourceBuffer, stored as a series of Chunks.
FallibleTArray<Chunk> mChunks;
/// Consumers which are waiting to be notified when new data is available.
nsTArray<RefPtr<IResumable>> mWaitingConsumers;
/// If present, marks this SourceBuffer complete with the given final status.
Maybe<nsresult> mStatus;
/// Count of active consumers.
uint32_t mConsumerCount;
};
} // namespace image
} // namespace mozilla
#endif // mozilla_image_sourcebuffer_h