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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 "MediaCache.h"
#include "mozilla/Span.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
// or file accessible as an array of blocks, which supports a block move
// operation, and allows synchronous reading and writing from any thread, with
// writes being buffered as needed so as not to block.
// 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.
// Note it's also recommended not to read from the media cache from the main
// thread to prevent jank.
class MediaBlockCacheBase {
MediaCacheStream::BLOCK_SIZE <
"MediaCacheStream::BLOCK_SIZE should fit in 31 bits");
static const int32_t BLOCK_SIZE = MediaCacheStream::BLOCK_SIZE;
virtual ~MediaBlockCacheBase() = default;
// Initialize this cache.
virtual nsresult Init() = 0;
// Erase data and discard pending changes to reset the cache to its pristine
// state as it was after Init().
virtual void Flush() = 0;
// Maximum number of blocks expected in this block cache. (But allow overflow
// to accomodate incoming traffic before MediaCache can handle it.)
virtual size_t GetMaxBlocks(size_t aCacheSizeInKiB) const = 0;
// Can be called on any thread. This defers to a non-main thread.
virtual nsresult WriteBlock(uint32_t aBlockIndex, Span<const uint8_t> aData1,
Span<const uint8_t> aData2) = 0;
// Synchronously reads data from file. May read from file or memory
// depending on whether written blocks have been flushed to file yet.
// Not recommended to be called from the main thread, as can cause jank.
virtual nsresult Read(int64_t aOffset, uint8_t* aData, int32_t aLength,
int32_t* aBytes) = 0;
// Moves a block asynchronously. Can be called on any thread.
// This defers file I/O to a non-main thread.
virtual nsresult MoveBlock(int32_t aSourceBlockIndex,
int32_t aDestBlockIndex) = 0;
} // End namespace mozilla.