[PPAPI] Implement an IOStreamResource for data transmission between plugin and renderer.

ppapi/shared_impl/circular_buffer.h

+// Copyright (c) 2012 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 PPAPI_SHARED_IMPL_CIRCULAR_BUFFER_H_
+#define PPAPI_SHARED_IMPL_CIRCULAR_BUFFER_H_
+
+#include "base/basictypes.h"
+#include "ppapi/shared_impl/ppapi_shared_export.h"
+
+namespace ppapi {
+
+class PPAPI_SHARED_EXPORT CircularBuffer {
+ public:
+  // Construct a CircularBuffer by given underlying buffer and size.
+  CircularBuffer(void* buffer, uint32_t size);
+
+  ~CircularBuffer();
+
+  // Remaining buffer size for reading or writing.
+  uint32_t remaining() const {
+    if (position_ < limit_)
+      return limit_ - position_;
+    if (position_ > limit_)
+      return buffer_size_ + limit_ - position_;
+    return maybe_empty_ ? 0 : buffer_size_;
+  }

[bbudge, 2013/12/31 00:51:53]

This is a bit long and complicated to be an inline using the getter style (lower
case).

[Peng, 2013/12/31 23:33:54]

Add remaining_ field, and this function returns it directly.

Done

+
+  // Moves position forward by given offset.
+  void MovePosition(uint32_t offset);
+
+  // Moves limit forward by given offset.
+  void MoveLimit(uint32_t offset);
+
+  // Reads data and move position forward. The actual read size will be
+  // returned.
+  int32_t Read(void* buffer, uint32_t size);
+
+  // Similar to |Read()|, but it will fail, if the circular buffer does not have
+  // enough data.
+  int32_t ReadAll(void* buffer, uint32_t size);
+
+  // Writes data and move position forward. The actual write size will be
+  // returned.
+  int32_t Write(const void* buffer, uint32_t size);
+
+  // Similar to |Write()|, but it will fail, if the circular buffer does not
+  // have enough space for the given size of data.
+  int32_t WriteAll(const void* buffer, uint32_t size);
+
+  // Locks the given size of underlying buffer for direct accessing.
+  int32_t Lock(void** buffer, uint32_t size);
+
+  // Relocks underlying buffer. It is used for adjusting locked block size;
+  int32_t Relock(void* buffer, uint32_t size);
+
+  // Unlocks buffer which is locked by previous |Lock()| call. The locked block
+  // size will be returned.
+  int32_t Unlock(const void* buffer);
+
+  // Returns true if the circular buffer is locked.
+  bool IsLocked() const { return locked_buffer_; }
+
+ private:
+  int32_t ReadInternal(void* buffer, uint32_t size);
+
+  int32_t WriteInternal(const void* buffer, uint32_t size);
+
+  // Underlying buffer pointer.
+  uint8_t* buffer_;
+
+  // Underlying buffer size.
+  uint32_t buffer_size_;
+
+  // Current position for reading or writing.
+  uint32_t position_;
+
+  // The limit position for reading or writing.
+  uint32_t limit_;
+
+  // When position_ is equal to limit_, use this value to indicate the buffer is
+  // empty or full.
+  bool maybe_empty_;

[bbudge, 2013/12/31 00:51:53]

It's a little hard to understand how this works. Why not add a remaining_ field
and keep it up to date in MovePosition and MoveLimit?

[Peng, 2013/12/31 23:33:54]

Done.

+
+  // Locked buffer pointer returned by |Lock()|. It will be reset to NULL,
+  // When |Unlock()| is called.
+  uint8_t* locked_buffer_;
+
+  // Locked buffer size.
+  uint32_t locked_buffer_size_;
+
+  DISALLOW_COPY_AND_ASSIGN(CircularBuffer);
+};
+
+}  // namespace ppapi
+
+#endif  // PPAPI_SHARED_IMPL_CIRCULAR_BUFFER_H_