зеркало из https://github.com/mozilla/gecko-dev.git
80 строки
3.2 KiB
C++
80 строки
3.2 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim:set ts=2 sw=2 sts=2 et cindent: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this file,
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* You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef MEDIA_BLOCK_CACHE_BASE_H_
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#define MEDIA_BLOCK_CACHE_BASE_H_
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#include "MediaCache.h"
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#include "mozilla/Span.h"
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namespace mozilla {
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// Manages block management for the media cache. Data comes in over the network
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// via callbacks on the main thread, however we don't want to write the
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// incoming data to the media cache on the main thread, as this could block
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// causing UI jank.
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//
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// So MediaBlockCacheBase provides an abstraction for a temporary memory buffer
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// or file accessible as an array of blocks, which supports a block move
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// operation, and allows synchronous reading and writing from any thread, with
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// writes being buffered as needed so as not to block.
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//
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// Writes and cache block moves (which require reading) may be deferred to
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// their own non-main thread. This object also ensures that data which has
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// been scheduled to be written, but hasn't actually *been* written, is read
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// as if it had, i.e. pending writes are cached in readable memory until
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// they're flushed to file.
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//
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// To improve efficiency, writes can only be done at block granularity,
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// whereas reads can be done with byte granularity.
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//
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// Note it's also recommended not to read from the media cache from the main
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// thread to prevent jank.
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class MediaBlockCacheBase {
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public:
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NS_INLINE_DECL_THREADSAFE_REFCOUNTING(MediaBlockCacheBase)
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static_assert(MediaCacheStream::BLOCK_SIZE <
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static_cast<std::remove_const<decltype(
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MediaCacheStream::BLOCK_SIZE)>::type>(INT32_MAX),
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"MediaCacheStream::BLOCK_SIZE should fit in 31 bits");
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static const int32_t BLOCK_SIZE = MediaCacheStream::BLOCK_SIZE;
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protected:
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virtual ~MediaBlockCacheBase() = default;
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public:
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// Initialize this cache.
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virtual nsresult Init() = 0;
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// Erase data and discard pending changes to reset the cache to its pristine
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// state as it was after Init().
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virtual void Flush() = 0;
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// Maximum number of blocks expected in this block cache. (But allow overflow
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// to accomodate incoming traffic before MediaCache can handle it.)
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virtual size_t GetMaxBlocks(size_t aCacheSizeInKiB) const = 0;
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// Can be called on any thread. This defers to a non-main thread.
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virtual nsresult WriteBlock(uint32_t aBlockIndex, Span<const uint8_t> aData1,
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Span<const uint8_t> aData2) = 0;
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// Synchronously reads data from file. May read from file or memory
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// depending on whether written blocks have been flushed to file yet.
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// Not recommended to be called from the main thread, as can cause jank.
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virtual nsresult Read(int64_t aOffset, uint8_t* aData, int32_t aLength,
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int32_t* aBytes) = 0;
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// Moves a block asynchronously. Can be called on any thread.
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// This defers file I/O to a non-main thread.
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virtual nsresult MoveBlock(int32_t aSourceBlockIndex,
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int32_t aDestBlockIndex) = 0;
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};
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} // End namespace mozilla.
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#endif /* MEDIA_BLOCK_CACHE_BASE_H_ */
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