Index: content/common/one_writer_seqlock.h |
diff --git a/content/common/one_writer_seqlock.h b/content/common/one_writer_seqlock.h |
new file mode 100644 |
index 0000000000000000000000000000000000000000..6774df6c0156a467041dd8c29445bcc85777cea5 |
--- /dev/null |
+++ b/content/common/one_writer_seqlock.h |
@@ -0,0 +1,46 @@ |
+// Copyright (c) 2011 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. |
+ |
+#ifndef CONTENT_COMMON_ONE_WRITER_SEQLOCK_H_ |
+#define CONTENT_COMMON_ONE_WRITER_SEQLOCK_H_ |
+ |
+#include "base/atomicops.h" |
+#include "base/threading/platform_thread.h" |
+#include "content/common/content_export.h" |
+ |
+namespace content { |
+ |
+// This SeqLock handles only *one* writer and multiple readers. It may be |
+// suitable for low-contention with relatively infrequent writes, and many |
+// readers. See: |
+// http://en.wikipedia.org/wiki/Seqlock |
+// http://www.concurrencykit.org/doc/ck_sequence.html |
+// This implementation is based on ck_sequence.h from http://concurrencykit.org. |
+// |
+// Currently this type of lock is used in two implementations (gamepad and |
+// device motion, in particular see e.g. shared_memory_seqlock_buffer.h). |
+// It may make sense to generalize this lock to multiple writers. |
+// |
+// You must be very careful not to operate on potentially inconsistent read |
+// buffers. If the read must be retry'd, the data in the read buffer could |
+// contain any random garbage. e.g., contained pointers might be |
+// garbage, or indices could be out of range. Probably the only suitable thing |
+// to do during the read loop is to make a copy of the data, and operate on it |
+// only after the read was found to be consistent. |
+class CONTENT_EXPORT OneWriterSeqLock { |
darin (slow to review)
2013/06/24 23:40:34
nit: Since you didn't freshly write these files, c
timvolodine
2013/06/25 03:36:07
Done.
|
+ public: |
+ OneWriterSeqLock(); |
+ base::subtle::Atomic32 ReadBegin(); |
+ bool ReadRetry(base::subtle::Atomic32 version); |
+ void WriteBegin(); |
+ void WriteEnd(); |
+ |
+ private: |
+ base::subtle::Atomic32 sequence_; |
+ DISALLOW_COPY_AND_ASSIGN(OneWriterSeqLock); |
+}; |
+ |
+} // namespace content |
+ |
+#endif // CONTENT_COMMON_ONE_WRITER_SEQLOCK_H_ |