Multi reader/writer cache/buffer

media/blink/multibuffer_reader.h

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef MEDIA_BLINK_MULTIBUFFER_READER_H_
+#define MEDIA_BLINK_MULTIBUFFER_READER_H_
+
+#include <stdint.h>
+
+#include <limits>
+#include <map>
+#include <set>
+
+#include "media/blink/multibuffer.h"
+
+namespace media {
+
+// Wrapper for MultiBuffer that offers a simple byte-reading
+// interface with prefetch.
+class MultiBufferReader : public MultiBuffer::Reader {
+ public:
+  // Note that |progress_callback| is guaranteed to be called if
+  // a redirect happens and the url_data is updated. Otherwise
+  // origin checks will become insecure.
+  // Users probably want to call SetMaxBuffer & SetPreload after
+  // creating the a MultiBufferReader.
+  // The progress callback will be called when the "available range"
+  // changes. (The number of bytes available for reading before and
+  // after the current position.) The arguments for the progress
+  // callback is the first byte available (from beginning of file)
+  // and the last byte available + 1. Note that there may be other
+  // regions of available data in the cache as well.
+  MultiBufferReader(MultiBuffer* multibuffer,
+                    MultiBufferUrlData url_data,
+                    int64_t start,
+                    int64_t end,
+                    base::Callback<void(int64_t, int64_t)> progress_callback);
+
+  ~MultiBufferReader() override;
+
+  // Returns number of bytes available for reading. When the rest of the file
+  // is available, the number returned will be greater than the number
+  // or readable bytes. If an error occurs, -1 is returned.
+  int64_t Available() const;
+
+  // Seek to a different position.
+  // If there is a pending Wait(), it will be cancelled.
+  void Seek(int64_t pos);
+
+  // Returns the current position.
+  int64_t Tell() const { return pos_; }
+
+  // Tries to read |len| bytes and advance position.
+  // Returns number of bytes read.
+  // If there is a pending Wait(), it will be cancelled.
+  int64_t TryRead(unsigned char *data, int64_t len);
+
+  // Wait until |len| bytes are available for reading.
+  // Returns net::OK if |len| bytes are already available, otherwise it will
+  // return net::ERR_IO_PENDING and call |cb| at some point later.
+  // |len| must be smaller or equal to max_buffer_forward.
+  int Wait(int64_t len, base::Closure cb);
+
+  // Set how much data we try to preload into the cache ahead of our current
+  // location. Normally, we preload until we have preload_high bytes, then
+  // stop until we fall below preload_low bytes. Note that preload can be
+  // set higher than max_buffer_forward, but the result is usually that
+  // some blocks will be freed between the current position and the preload
+  // position.
+  void SetPreload(int64_t preload_high, int64_t preload_low);
+
+  // Adjusts max_buffer_forward and max_buffer_backsard.

[liberato (no reviews please), 2015/10/14 14:51:34]

one will ask "what is max_buffer_*".  might as well mention it here rather than
making them find the comment for |max_buffer_forward_|.

also, s/sard/ward/

[hubbe, 2015/10/16 00:17:44]

Comment updated.

+  void SetMaxBuffer(int64_t backward, int64_t forward);
+
+  // Returns true if we are currently loading data.
+  bool IsLoading() const;
+
+  // Reader implementation.
+  void NotifyAvailableRange(
+      const Range<MultiBufferBlockId>& range) override;
+  void UpdateUrlData(const MultiBufferUrlData& old_url_data,
+                     const MultiBufferUrlData& new_url_data) override;
+
+  // Getters
+  MultiBufferUrlData GetUrlData() const { return url_data_; }
+  int64_t preload_high() const { return preload_high_; }
+  int64_t preload_low() const { return preload_low_; }
+
+ private:
+  // Returns the block for a particular byte position.
+  MultiBufferBlockId block(int64_t byte_pos) const;
+
+  // Returns the block for a particular byte position, rounding up.
+  MultiBufferBlockId block_ceil(int64_t byte_pos) const;
+
+  // Check if wait operation can complete now.
+  // Returns false if this object was destroyed while calling the
+  // wait callback, true otherwise.
+  bool CheckWait();
+
+  // Increment preload position if data has been added to the buffer.
+  // Returns false if this object was destroyed, true otherwise.
+  bool IncrementPreloadPos();
+
+  // The ID of the url we're accessing.
+  MultiBufferUrlData url_data_;
+
+  // We're not interested in reading past this position.
+  int64_t end_;
+
+  // Defer reading once we have this much data.
+  int64_t preload_high_;
+  // Stop deferring once we have this much data.
+  int64_t preload_low_;
+
+  // Pin this much data in the cache from the current position.
+  int64_t max_buffer_forward_;
+  int64_t max_buffer_backward_;
+
+  // Current position in bytes.
+  int64_t pos_;
+
+  // [block(pos_)..preload_pos_) are known to be in the cache.
+  // preload_pos_ is only allowed to point to a filled
+  // cache position if it is equal to end_ or pos_+preload_.
+  // This is a pointer to a slot in the cache, so the unit is
+  // blocks.
+  MultiBufferBlockId preload_pos_;
+
+  // True if we've requested data from the cache by calling WaitFor().
+  bool loading_;
+
+  // When Available() > current_wait_size_ we call cb_.
+  int64_t current_wait_size_;
+  base::Closure cb_;
+
+  // Progress callback.
+  base::Callback<void(int64_t, int64_t)> progress_callback_;
+
+  // Hack to let us detect if we've been deleted when calling a callback.
+  bool* clear_on_delete_;
+
+  // The multibuffer we're wrapping, not owned.
+  MultiBuffer* multibuffer_;
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BLINK_MULTIBUFFER_READER_H_