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| 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 #include "content/renderer/shared_memory_seqlock_reader.h" | |
| 6 | |
| 7 namespace content { | |
| 8 namespace internal { | |
| 9 | |
| 10 SharedMemorySeqLockReaderBase::SharedMemorySeqLockReaderBase() { } | |
| 11 | |
| 12 SharedMemorySeqLockReaderBase::~SharedMemorySeqLockReaderBase() { } | |
| 13 | |
| 14 void* | |
| 15 SharedMemorySeqLockReaderBase::InitializeSharedMemory( | |
| 16 base::SharedMemoryHandle shared_memory_handle, size_t buffer_size) { | |
| 17 renderer_shared_memory_handle_ = shared_memory_handle; | |
| 18 if (!base::SharedMemory::IsHandleValid(renderer_shared_memory_handle_)) | |
| 19 return 0; | |
| 20 renderer_shared_memory_.reset(new base::SharedMemory( | |
| 21 renderer_shared_memory_handle_, true)); | |
| 22 | |
| 23 return (renderer_shared_memory_->Map(buffer_size)) | |
| 24 ? renderer_shared_memory_->memory() | |
| 25 : 0; | |
| 26 } | |
| 27 | |
| 28 bool SharedMemorySeqLockReaderBase::FetchFromBuffer( | |
| 29 content::OneWriterSeqLock* seqlock, void* final, void* temp, void* from, | |
| 30 size_t size) { | |
| 31 | |
| 32 if (!base::SharedMemory::IsHandleValid(renderer_shared_memory_handle_)) | |
| 33 return false; | |
| 34 | |
| 35 // Only try to read this many times before failing to avoid waiting here | |
| 36 // very long in case of contention with the writer. | |
| 37 int contention_count = -1; | |
| 38 base::subtle::Atomic32 version; | |
| 39 do { | |
| 40 version = seqlock->ReadBegin(); | |
| 41 memcpy(temp, from, size); | |
| 42 ++contention_count; | |
| 43 if (contention_count == kMaximumContentionCount) | |
| 44 break; | |
| 45 } while (seqlock->ReadRetry(version)); | |
| 46 | |
| 47 if (contention_count >= kMaximumContentionCount) { | |
| 48 // We failed to successfully read, presumably because the hardware | |
| 49 // thread was taking unusually long. Don't copy the data to the output | |
| 50 // buffer, and simply leave what was there before. | |
| 51 return false; | |
| 52 } | |
| 53 | |
| 54 // New data was read successfully, copy it into the output buffer. | |
| 55 memcpy(final, temp, size); | |
| 56 return true; | |
| 57 } | |
| 58 | |
| 59 } // namespace internal | |
| 60 } // namespace content | |
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