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Side by Side Diff: components/shared_memory_seqlock/one_writer_seqlock.h

Issue 1164563003: Extract device_sensors to /device via Mojofication (Closed) Base URL: https://chromium.googlesource.com/chromium/src.git@master
Patch Set: Created 5 years, 6 months ago
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1 // Copyright 2013 The Chromium Authors. All rights reserved. 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 2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file. 3 // found in the LICENSE file.
4 4
5 #ifndef CONTENT_COMMON_ONE_WRITER_SEQLOCK_H_ 5 #ifndef COMPONENTS_SHARED_MEMORY_SEQLOCK_ONE_WRITER_SEQLOCK_H_
6 #define CONTENT_COMMON_ONE_WRITER_SEQLOCK_H_ 6 #define COMPONENTS_SHARED_MEMORY_SEQLOCK_ONE_WRITER_SEQLOCK_H_
7 7
8 #include "base/atomicops.h" 8 #include "base/atomicops.h"
9 #include "base/threading/platform_thread.h" 9 #include "base/threading/platform_thread.h"
10 #include "content/common/content_export.h"
11 10
12 namespace content { 11 namespace shared_memory_seqlock {
13 12
14 // This SeqLock handles only *one* writer and multiple readers. It may be 13 // This SeqLock handles only *one* writer and multiple readers. It may be
15 // suitable for low-contention with relatively infrequent writes, and many 14 // suitable for low-contention with relatively infrequent writes, and many
16 // readers. See: 15 // readers. See:
17 // http://en.wikipedia.org/wiki/Seqlock 16 // http://en.wikipedia.org/wiki/Seqlock
18 // http://www.concurrencykit.org/doc/ck_sequence.html 17 // http://www.concurrencykit.org/doc/ck_sequence.html
19 // This implementation is based on ck_sequence.h from http://concurrencykit.org. 18 // This implementation is based on ck_sequence.h from http://concurrencykit.org.
20 // 19 //
21 // Currently this type of lock is used in two implementations (gamepad and 20 // Currently this type of lock is used in two implementations (gamepad and
22 // device motion, in particular see e.g. shared_memory_seqlock_buffer.h). 21 // device motion, in particular see e.g. shared_memory_seqlock_buffer.h).
23 // It may make sense to generalize this lock to multiple writers. 22 // It may make sense to generalize this lock to multiple writers.
24 // 23 //
25 // You must be very careful not to operate on potentially inconsistent read 24 // You must be very careful not to operate on potentially inconsistent read
26 // buffers. If the read must be retry'd, the data in the read buffer could 25 // buffers. If the read must be retry'd, the data in the read buffer could
27 // contain any random garbage. e.g., contained pointers might be 26 // contain any random garbage. e.g., contained pointers might be
28 // garbage, or indices could be out of range. Probably the only suitable thing 27 // garbage, or indices could be out of range. Probably the only suitable thing
29 // to do during the read loop is to make a copy of the data, and operate on it 28 // to do during the read loop is to make a copy of the data, and operate on it
30 // only after the read was found to be consistent. 29 // only after the read was found to be consistent.
31 class CONTENT_EXPORT OneWriterSeqLock { 30 class OneWriterSeqLock {
32 public: 31 public:
33 OneWriterSeqLock(); 32 OneWriterSeqLock();
34 base::subtle::Atomic32 ReadBegin(); 33 base::subtle::Atomic32 ReadBegin();
35 bool ReadRetry(base::subtle::Atomic32 version); 34 bool ReadRetry(base::subtle::Atomic32 version);
36 void WriteBegin(); 35 void WriteBegin();
37 void WriteEnd(); 36 void WriteEnd();
38 37
39 private: 38 private:
40 base::subtle::Atomic32 sequence_; 39 base::subtle::Atomic32 sequence_;
41 DISALLOW_COPY_AND_ASSIGN(OneWriterSeqLock); 40 DISALLOW_COPY_AND_ASSIGN(OneWriterSeqLock);
42 }; 41 };
43 42
44 } // namespace content 43 } // namespace shared_memory_seqlock
45 44
46 #endif // CONTENT_COMMON_ONE_WRITER_SEQLOCK_H_ 45 #endif // COMPONENTS_SHARED_MEMORY_SEQLOCK_ONE_WRITER_SEQLOCK_H_
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