1 files changed, 87 insertions, 0 deletions
diff --git a/dom/media/MemoryBlockCache.h b/dom/media/MemoryBlockCache.h
new file mode 100644
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--- /dev/null
+++ b/dom/media/MemoryBlockCache.h
@@ -0,0 +1,87 @@
+/* -*- 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 http://mozilla.org/MPL/2.0/. */
+
+#ifndef MEMORY_BLOCK_CACHE_H_
+#define MEMORY_BLOCK_CACHE_H_
+
+#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 {
+ public:
+  explicit MemoryBlockCache(int64_t aContentLength);
+
+ protected:
+  virtual ~MemoryBlockCache();
+
+ public:
+  // 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;
+
+ private:
+  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.
+  Mutex mMutex MOZ_UNANNOTATED;
+
+  nsTArray<uint8_t> mBuffer;
+  bool mHasGrown = false;
+};
+
+}  // End namespace mozilla.
+
+#endif /* MEMORY_BLOCK_CACHE_H_ */