MediaBlockCacheBase.h (3280B)
1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ 2 /* vim:set ts=2 sw=2 sts=2 et cindent: */ 3 /* This Source Code Form is subject to the terms of the Mozilla Public 4 * License, v. 2.0. If a copy of the MPL was not distributed with this file, 5 * You can obtain one at http://mozilla.org/MPL/2.0/. */ 6 7 #ifndef MEDIA_BLOCK_CACHE_BASE_H_ 8 #define MEDIA_BLOCK_CACHE_BASE_H_ 9 10 #include "MediaCache.h" 11 #include "mozilla/Span.h" 12 13 namespace mozilla { 14 15 // Manages block management for the media cache. Data comes in over the network 16 // via callbacks on the main thread, however we don't want to write the 17 // incoming data to the media cache on the main thread, as this could block 18 // causing UI jank. 19 // 20 // So MediaBlockCacheBase provides an abstraction for a temporary memory buffer 21 // or file accessible as an array of blocks, which supports a block move 22 // operation, and allows synchronous reading and writing from any thread, with 23 // writes being buffered as needed so as not to block. 24 // 25 // Writes and cache block moves (which require reading) may be deferred to 26 // their own non-main thread. This object also ensures that data which has 27 // been scheduled to be written, but hasn't actually *been* written, is read 28 // as if it had, i.e. pending writes are cached in readable memory until 29 // they're flushed to file. 30 // 31 // To improve efficiency, writes can only be done at block granularity, 32 // whereas reads can be done with byte granularity. 33 // 34 // Note it's also recommended not to read from the media cache from the main 35 // thread to prevent jank. 36 class MediaBlockCacheBase { 37 public: 38 NS_INLINE_DECL_THREADSAFE_REFCOUNTING(MediaBlockCacheBase) 39 40 static_assert( 41 MediaCacheStream::BLOCK_SIZE < 42 static_cast< 43 std::remove_const<decltype(MediaCacheStream::BLOCK_SIZE)>::type>( 44 INT32_MAX), 45 "MediaCacheStream::BLOCK_SIZE should fit in 31 bits"); 46 static constexpr int32_t BLOCK_SIZE = MediaCacheStream::BLOCK_SIZE; 47 48 protected: 49 virtual ~MediaBlockCacheBase() = default; 50 51 public: 52 // Initialize this cache. 53 virtual nsresult Init() = 0; 54 55 // Erase data and discard pending changes to reset the cache to its pristine 56 // state as it was after Init(). 57 virtual void Flush() = 0; 58 59 // Maximum number of blocks expected in this block cache. (But allow overflow 60 // to accomodate incoming traffic before MediaCache can handle it.) 61 virtual size_t GetMaxBlocks(size_t aCacheSizeInKiB) const = 0; 62 63 // Can be called on any thread. This defers to a non-main thread. 64 virtual nsresult WriteBlock(uint32_t aBlockIndex, Span<const uint8_t> aData1, 65 Span<const uint8_t> aData2) = 0; 66 67 // Synchronously reads data from file. May read from file or memory 68 // depending on whether written blocks have been flushed to file yet. 69 // Not recommended to be called from the main thread, as can cause jank. 70 virtual nsresult Read(int64_t aOffset, uint8_t* aData, int32_t aLength) = 0; 71 72 // Moves a block asynchronously. Can be called on any thread. 73 // This defers file I/O to a non-main thread. 74 virtual nsresult MoveBlock(int32_t aSourceBlockIndex, 75 int32_t aDestBlockIndex) = 0; 76 }; 77 78 } // End namespace mozilla. 79 80 #endif /* MEDIA_BLOCK_CACHE_BASE_H_ */