dom/media/MemoryBlockCache.h

   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 MEMORY_BLOCK_CACHE_H_
   8 #define MEMORY_BLOCK_CACHE_H_
   9
  10 #include "MediaBlockCacheBase.h"
  11 #include "mozilla/Mutex.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 // as an array of blocks, which supports a block move operation, and
  22 // allows synchronous reading and writing from any thread.
  23 //
  24 // Writes and cache block moves (which require reading) may be deferred to
  25 // their own non-main thread. This object also ensures that data which has
  26 // been scheduled to be written, but hasn't actually *been* written, is read
  27 // as if it had, i.e. pending writes are cached in readable memory until
  28 // they're flushed to file.
  29 //
  30 // To improve efficiency, writes can only be done at block granularity,
  31 // whereas reads can be done with byte granularity.
  32 class MemoryBlockCache : public MediaBlockCacheBase {
  33  public:
  34   explicit MemoryBlockCache(int64_t aContentLength);
  35
  36  protected:
  37   virtual ~MemoryBlockCache();
  38
  39  public:
  40   // Allocate initial buffer.
  41   // If re-initializing, clear buffer.
  42   virtual nsresult Init() override;
  43
  44   void Flush() override;
  45
  46   // Maximum number of blocks allowed in this block cache.
  47   // Based on initial content length, and minimum usable block cache.
  48   size_t GetMaxBlocks(size_t) const override { return mMaxBlocks; }
  49
  50   // Can be called on any thread.
  51   virtual nsresult WriteBlock(uint32_t aBlockIndex, Span<const uint8_t> aData1,
  52                               Span<const uint8_t> aData2) override;
  53
  54   // Synchronously reads data from buffer.
  55   virtual nsresult Read(int64_t aOffset, uint8_t* aData, int32_t aLength,
  56                         int32_t* aBytes) override;
  57
  58   // Moves a block. Can be called on any thread.
  59   virtual nsresult MoveBlock(int32_t aSourceBlockIndex,
  60                              int32_t aDestBlockIndex) override;
  61
  62  private:
  63   static size_t BlockIndexToOffset(uint32_t aBlockIndex) {
  64     return static_cast<size_t>(aBlockIndex) * BLOCK_SIZE;
  65   }
  66
  67   // Ensure the buffer has at least a multiple of BLOCK_SIZE that can contain
  68   // aContentLength bytes. Buffer size can only grow.
  69   // Returns false if allocation failed.
  70   bool EnsureBufferCanContain(size_t aContentLength);
  71
  72   // Initial content length.
  73   const size_t mInitialContentLength;
  74
  75   // Maximum number of blocks that this MemoryBlockCache expects.
  76   const size_t mMaxBlocks;
  77
  78   // Mutex which controls access to all members below.
  79   Mutex mMutex MOZ_UNANNOTATED;
  80
  81   nsTArray<uint8_t> mBuffer;
  82   bool mHasGrown = false;
  83 };
  84
  85 }  // End namespace mozilla.
  86
  87 #endif /* MEMORY_BLOCK_CACHE_H_ */