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      1 // Copyright (c) 2015 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 // Note: ported from Chromium commit head: 60f9667
      5 
      6 #ifndef SHARED_MEMORY_REGION_H_
      7 #define SHARED_MEMORY_REGION_H_
      8 
      9 #include "base/memory/shared_memory.h"
     10 #include "bitstream_buffer.h"
     11 
     12 namespace media {
     13 
     14 // Helper class to access a region of a SharedMemory. Different from
     15 // SharedMemory, in which the |offset| of function MapAt() must be aligned to
     16 // the value of |SysInfo::VMAllocationGranularity()|, the |offset| of a
     17 // SharedMemoryRegion needs not to be aligned, this class hides the details
     18 // and returns the mapped address of the given offset.
     19 class SharedMemoryRegion {
     20  public:
     21   // Creates a SharedMemoryRegion.
     22   // The mapped memory region begins at |offset| bytes from the start of the
     23   // shared memory and the length is |size|. It will take the ownership of
     24   // the |handle| and release the resource when being destroyed. Different
     25   // from SharedMemory, the |offset| needs not to be aligned to the value of
     26   // |SysInfo::VMAllocationGranularity()|.
     27   SharedMemoryRegion(const base::SharedMemoryHandle& handle,
     28                      off_t offset,
     29                      size_t size,
     30                      bool read_only);
     31 
     32   // Creates a SharedMemoryRegion from the given |bistream_buffer|.
     33   SharedMemoryRegion(const BitstreamBuffer& bitstream_buffer, bool read_only);
     34 
     35   // Maps the shared memory into the caller's address space.
     36   // Return true on success, false otherwise.
     37   bool Map();
     38 
     39   // Gets a pointer to the mapped region if it has been mapped via Map().
     40   // Returns |nullptr| if it is not mapped. The returned pointer points
     41   // to the memory at the offset previously passed to the constructor.
     42   void* memory();
     43 
     44   size_t size() const { return size_; }
     45 
     46  private:
     47   base::SharedMemory shm_;
     48   off_t offset_;
     49   size_t size_;
     50   size_t alignment_size_;
     51 
     52   DISALLOW_COPY_AND_ASSIGN(SharedMemoryRegion);
     53 };
     54 
     55 }  // namespace media
     56 
     57 #endif  // SHARED_MEMORY_REGION_H_
     58