content/renderer/shared_memory_seqlock_reader.h

   1 // Copyright 2013 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef CONTENT_RENDERER_SHARED_MEMORY_SEQLOCK_READER_H_
   6 #define CONTENT_RENDERER_SHARED_MEMORY_SEQLOCK_READER_H_
   7
   8 #include "base/logging.h"
   9 #include "base/memory/scoped_ptr.h"
  10 #include "base/memory/shared_memory.h"
  11 #include "content/common/shared_memory_seqlock_buffer.h"
  12
  13 namespace content {
  14 namespace internal {
  15
  16 class SharedMemorySeqLockReaderBase  {
  17  protected:
  18   SharedMemorySeqLockReaderBase();
  19   virtual ~SharedMemorySeqLockReaderBase();
  20
  21   void* InitializeSharedMemory(
  22       base::SharedMemoryHandle shared_memory_handle,
  23       size_t buffer_size);
  24
  25   bool FetchFromBuffer(content::OneWriterSeqLock* seqlock, void* final,
  26       void* temp, void* from, size_t size);
  27
  28   static const int kMaximumContentionCount = 10;
  29   base::SharedMemoryHandle renderer_shared_memory_handle_;
  30   scoped_ptr<base::SharedMemory> renderer_shared_memory_;
  31 };
  32
  33 }  // namespace internal
  34
  35 // Template argument Data should be a pod-like structure only containing
  36 // data fields, such that it is copyable by memcpy method.
  37 template<typename Data>
  38 class SharedMemorySeqLockReader
  39     : private internal::SharedMemorySeqLockReaderBase {
  40  public:
  41   SharedMemorySeqLockReader() : buffer_(0) { }
  42   virtual ~SharedMemorySeqLockReader() { }
  43
  44   bool GetLatestData(Data* data) {
  45     DCHECK(buffer_);
  46     DCHECK(sizeof(*data) == sizeof(*temp_buffer_));
  47     return FetchFromBuffer(&buffer_->seqlock, data, temp_buffer_.get(),
  48         &buffer_->data, sizeof(*temp_buffer_));
  49   }
  50
  51   bool Initialize(base::SharedMemoryHandle shared_memory_handle) {
  52     if (void* memory = InitializeSharedMemory(
  53         shared_memory_handle, sizeof(SharedMemorySeqLockBuffer<Data>))) {
  54       buffer_ = static_cast<SharedMemorySeqLockBuffer<Data>*>(memory);
  55       temp_buffer_.reset(new Data);
  56       return true;
  57     }
  58     return false;
  59   }
  60
  61  private:
  62   SharedMemorySeqLockBuffer<Data>* buffer_;
  63   scoped_ptr<Data> temp_buffer_;
  64
  65   DISALLOW_COPY_AND_ASSIGN(SharedMemorySeqLockReader);
  66 };
  67
  68 }  // namespace content
  69
  70 #endif  // CONTENT_RENDERER_SHARED_MEMORY_SEQLOCK_READER_H_