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/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim:set ts=2 sw=2 sts=2 et cindent: */
/* 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 */
#include "MediaBlockCacheBase.h"
#include "mozilla/Mutex.h"
namespace mozilla {
// Manages block management for the media cache. Data comes in over the network
// via callbacks on the main thread, however we don't want to write the
// incoming data to the media cache on the main thread, as this could block
// causing UI jank.
// So MediaBlockCacheBase provides an abstraction for a temporary memory buffer
// as an array of blocks, which supports a block move operation, and
// allows synchronous reading and writing from any thread.
// Writes and cache block moves (which require reading) may be deferred to
// their own non-main thread. This object also ensures that data which has
// been scheduled to be written, but hasn't actually *been* written, is read
// as if it had, i.e. pending writes are cached in readable memory until
// they're flushed to file.
// To improve efficiency, writes can only be done at block granularity,
// whereas reads can be done with byte granularity.
class MemoryBlockCache : public MediaBlockCacheBase {
explicit MemoryBlockCache(int64_t aContentLength);
virtual ~MemoryBlockCache();
// Allocate initial buffer.
// If re-initializing, clear buffer.
virtual nsresult Init() override;
void Flush() override;
// Maximum number of blocks allowed in this block cache.
// Based on initial content length, and minimum usable block cache.
size_t GetMaxBlocks(size_t) const override { return mMaxBlocks; }
// Can be called on any thread.
virtual nsresult WriteBlock(uint32_t aBlockIndex, Span<const uint8_t> aData1,
Span<const uint8_t> aData2) override;
// Synchronously reads data from buffer.
virtual nsresult Read(int64_t aOffset, uint8_t* aData, int32_t aLength,
int32_t* aBytes) override;
// Moves a block. Can be called on any thread.
virtual nsresult MoveBlock(int32_t aSourceBlockIndex,
int32_t aDestBlockIndex) override;
static size_t BlockIndexToOffset(uint32_t aBlockIndex) {
return static_cast<size_t>(aBlockIndex) * BLOCK_SIZE;
// Ensure the buffer has at least a multiple of BLOCK_SIZE that can contain
// aContentLength bytes. Buffer size can only grow.
// Returns false if allocation failed.
bool EnsureBufferCanContain(size_t aContentLength);
// Initial content length.
const size_t mInitialContentLength;
// Maximum number of blocks that this MemoryBlockCache expects.
const size_t mMaxBlocks;
// Mutex which controls access to all members below.
nsTArray<uint8_t> mBuffer;
bool mHasGrown = false;
} // End namespace mozilla.
#endif /* MEMORY_BLOCK_CACHE_H_ */