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.
5 #include "shared_memory_seqlock_reader.h"
10 SharedMemorySeqLockReaderBase::SharedMemorySeqLockReaderBase() { }
12 SharedMemorySeqLockReaderBase::~SharedMemorySeqLockReaderBase() { }
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_
))
20 renderer_shared_memory_
.reset(new base::SharedMemory(
21 renderer_shared_memory_handle_
, true));
23 return (renderer_shared_memory_
->Map(buffer_size
))
24 ? renderer_shared_memory_
->memory()
28 bool SharedMemorySeqLockReaderBase::FetchFromBuffer(
29 content::OneWriterSeqLock
* seqlock
, void* final
, void* temp
, void* from
,
32 if (!base::SharedMemory::IsHandleValid(renderer_shared_memory_handle_
))
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
;
40 version
= seqlock
->ReadBegin();
41 memcpy(temp
, from
, size
);
43 if (contention_count
== kMaximumContentionCount
)
45 } while (seqlock
->ReadRetry(version
));
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.
54 // New data was read successfully, copy it into the output buffer.
55 memcpy(final
, temp
, size
);
59 } // namespace internal
60 } // namespace content