Add multi_process_lock to chrome/common

chrome/common/multi_process_lock.h

+// Copyright (c) 2010 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 CHROME_COMMON_MULTI_PROCESS_LOCK_H_
+#define CHROME_COMMON_MULTI_PROCESS_LOCK_H_
+#pragma once
+
+#include <string>
+
+// Platform abstraction for a lock that can be shared between processes.
+// The process that owns the lock will release it on exit even if
+// the exit is due to a crash. Locks are not recursive.
+class MultiProcessLock {
+ public:
+
+  // The length of a multi process lock name is limited on Linux, so

[Mark Mentovai, 2010/11/15 23:42:55]

Multiprocess is spelled without a space, but you can use a hyphen if you like,
which would better match multi_process_lock and MultiProcessLock. Same on line
23.

[dmac, 2010/11/16 17:54:17]

Done.

+  // it is limited it on all platforms for consistency. This length does
+  // not include a terminator. This is defined in terms of UNIX_PATH_MAX-2 on

[Mark Mentovai, 2010/11/15 23:42:55]

You should have a COMPILE_ASSERT to guarantee this in _linux.cc.

In the COMPILE_ASSERT, you should probably use sizeof(sun_path) instead of
UNIX_PATH_MAX as the latter is nonstandard.

And spaces go around operators like - even when they’re in comments. :)

[dmac, 2010/11/16 17:54:17]

Done.

+  // Linux.
+  static const size_t MULTI_PROCESS_LOCK_NAME_MAX_LEN = 106;

[Mark Mentovai, 2010/11/15 23:42:55]

You need to #include <sys/types.h> before you can use size_t.

[dmac, 2010/11/16 17:54:17]

Didn't seem to be needed on any platform, but added it anyways.

+
+  // Factory method for creating a multi process lock.
+  // |name| is the name of the lock. The name has special meaning on Windows
+  // where the prefix can determine the namespace of the lock.
+  // See http://msdn.microsoft.com/en-us/library/aa382954(v=VS.85).aspx for
+  // details.
+  static MultiProcessLock* Create(const std::string& name);
+
+  virtual ~MultiProcessLock() { }
+
+  // Try to grab ownership of the lock.
+  virtual bool TryLock() = 0;
+
+  // Release ownership of the lock.
+  virtual void Unlock() = 0;
+};
+
+#endif  // CHROME_COMMON_MULTI_PROCESS_LOCK_H_