Index: content/renderer/shared_memory_seqlock_reader.cc |
diff --git a/content/renderer/shared_memory_seqlock_reader.cc b/content/renderer/shared_memory_seqlock_reader.cc |
new file mode 100644 |
index 0000000000000000000000000000000000000000..84dc91c13daf2b37852cc621e1a3c8028a1e4620 |
--- /dev/null |
+++ b/content/renderer/shared_memory_seqlock_reader.cc |
@@ -0,0 +1,58 @@ |
+// Copyright (c) 2013 The Chromium Authors. All rights reserved. |
+// Use of this source code is governed by a BSD-style license that can be |
+// found in the LICENSE file. |
+ |
+#include "shared_memory_seqlock_reader.h" |
+ |
+namespace internal { |
+ |
+SharedMemorySeqLockReaderBase::SharedMemorySeqLockReaderBase() { } |
+ |
+SharedMemorySeqLockReaderBase::~SharedMemorySeqLockReaderBase() { } |
+ |
+void* |
+SharedMemorySeqLockReaderBase::InitializeSharedMemory( |
+ base::SharedMemoryHandle shared_memory_handle, size_t buffer_size) { |
+ renderer_shared_memory_handle_ = shared_memory_handle; |
+ if (!base::SharedMemory::IsHandleValid(renderer_shared_memory_handle_)) |
+ return 0; |
+ renderer_shared_memory_.reset(new base::SharedMemory( |
+ renderer_shared_memory_handle_, true)); |
+ |
+ return (renderer_shared_memory_->Map(buffer_size)) |
+ ? renderer_shared_memory_->memory() |
+ : 0; |
+} |
+ |
+bool SharedMemorySeqLockReaderBase::FetchFromBuffer( |
+ content::OneWriterSeqLock* seqlock, void* final, void* temp, void* from, |
+ size_t size) { |
+ |
+ if (!base::SharedMemory::IsHandleValid(renderer_shared_memory_handle_)) |
+ return false; |
+ |
+ // Only try to read this many times before failing to avoid waiting here |
+ // very long in case of contention with the writer. |
+ int contention_count = -1; |
+ base::subtle::Atomic32 version; |
+ do { |
+ version = seqlock->ReadBegin(); |
+ memcpy(temp, from, size); |
+ ++contention_count; |
+ if (contention_count == kMaximumContentionCount) |
+ break; |
+ } while (seqlock->ReadRetry(version)); |
+ |
+ if (contention_count >= kMaximumContentionCount) { |
+ // We failed to successfully read, presumably because the hardware |
+ // thread was taking unusually long. Don't copy the data to the output |
+ // buffer, and simply leave what was there before. |
+ return false; |
+ } |
+ |
+ // New data was read successfully, copy it into the output buffer. |
+ memcpy(final, temp, size); |
+ return true; |
+} |
+ |
+} // namespace internal |