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 size()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