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1 // Copyright (c) 2012 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 #include "media/audio/shared_memory_util.h" | |
6 | |
7 #include "base/atomicops.h" | |
8 #include "base/logging.h" | |
9 | |
10 using base::subtle::Atomic32; | |
11 | |
12 static const uint32 kUnknownDataSize = static_cast<uint32>(-1); | |
13 | |
14 namespace media { | |
15 | |
16 // When transferring data in the shared memory, first word is size of data | |
17 // in bytes. Actual data starts immediately after it. | |
nfullagar
2012/08/17 00:52:07
Comment above: ...last word is size of data in byt
DaleCurtis
2012/08/17 02:27:45
Done.
| |
18 | |
19 uint32 TotalSharedMemorySizeInBytes(uint32 packet_size) { | |
20 // Need to reserve extra 4 bytes for size of data. | |
21 return packet_size + sizeof(Atomic32); | |
22 } | |
23 | |
24 uint32 PacketSizeSizeInBytes(uint32 shared_memory_created_size) { | |
25 return shared_memory_created_size - sizeof(Atomic32); | |
26 } | |
27 | |
28 uint32 GetActualDataSizeInBytes(base::SharedMemory* shared_memory, | |
29 uint32 shared_memory_size) { | |
30 char* ptr = static_cast<char*>(shared_memory->memory()) + shared_memory_size; | |
31 DCHECK_EQ(0u, reinterpret_cast<size_t>(ptr) & 3); | |
32 | |
33 // Actual data size stored at the end of the buffer. | |
34 uint32 actual_data_size = | |
35 base::subtle::Acquire_Load(reinterpret_cast<volatile Atomic32*>(ptr)); | |
36 return std::min(actual_data_size, shared_memory_size); | |
37 } | |
38 | |
39 void SetActualDataSizeInBytes(void* shared_memory_ptr, | |
40 uint32 shared_memory_size, | |
41 uint32 actual_data_size) { | |
42 char* ptr = static_cast<char*>(shared_memory_ptr) + shared_memory_size; | |
43 DCHECK_EQ(0u, reinterpret_cast<size_t>(ptr) & 3); | |
44 | |
45 // Set actual data size at the end of the buffer. | |
46 base::subtle::Release_Store(reinterpret_cast<volatile Atomic32*>(ptr), | |
47 actual_data_size); | |
48 } | |
49 | |
50 void SetActualDataSizeInBytes(base::SharedMemory* shared_memory, | |
51 uint32 shared_memory_size, | |
52 uint32 actual_data_size) { | |
53 SetActualDataSizeInBytes(shared_memory->memory(), | |
54 shared_memory_size, actual_data_size); | |
55 } | |
56 | |
57 void SetUnknownDataSize(base::SharedMemory* shared_memory, | |
58 uint32 shared_memory_size) { | |
59 SetActualDataSizeInBytes(shared_memory, shared_memory_size, kUnknownDataSize); | |
60 } | |
61 | |
62 bool IsUnknownDataSize(base::SharedMemory* shared_memory, | |
63 uint32 shared_memory_size) { | |
64 char* ptr = static_cast<char*>(shared_memory->memory()) + shared_memory_size; | |
65 DCHECK_EQ(0u, reinterpret_cast<size_t>(ptr) & 3); | |
66 | |
67 // Actual data size stored at the end of the buffer. | |
68 uint32 actual_data_size = | |
69 base::subtle::Acquire_Load(reinterpret_cast<volatile Atomic32*>(ptr)); | |
70 return actual_data_size == kUnknownDataSize; | |
71 } | |
72 | |
73 } // namespace media | |
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