[cros] RlzValueStore made protected by a cross-process lock and not persisted over browser lifetime…

rlz/lib/recursive_cross_process_lock_posix.h

Index: rlz/lib/recursive_cross_process_lock_posix.h
diff --git a/rlz/lib/recursive_cross_process_lock_posix.h b/rlz/lib/recursive_cross_process_lock_posix.h
new file mode 100644
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+++ b/rlz/lib/recursive_cross_process_lock_posix.h
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+// Copyright (c) 2012 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 RLZ_LIB_RECURSIVE_CROSS_PROCESS_LOCK_POSIX_H_
+#define RLZ_LIB_RECURSIVE_CROSS_PROCESS_LOCK_POSIX_H_
+
+#include <pthread.h>
+
+class FilePath;
+
+namespace rlz_lib {
+
+// Creating a recursive cross-process mutex on Windows is one line. On POSIX,
+// there's no primitive for that, so this lock is emulated by an in-process
+// mutex to get the recursive part, followed by a cross-process lock for the
+// cross-process part.
+// This is a struct so that it doesn't need a static initializer.
+struct RecursiveCrossProcessLock {
+  // Tries to acquire a recursive cross-process lock. Note that this _always_
+  // acquires the in-process lock (if it wasn't already acquired). The parent
+  // directory of |lock_file| must exist.
+  bool TryGetCrossProcessLock(const FilePath& lock_filename);
+
+  // Releases the lock. Should always be called, even if
+  // TryGetCrossProcessLock() returned |false|.
+  void ReleaseLock();
+
+  pthread_mutex_t recursive_lock_;
+  pthread_t locking_thread_;
+
+  int file_lock_;
+};
+
+// On Mac, PTHREAD_RECURSIVE_MUTEX_INITIALIZER doesn't exist before 10.7 and
+// is buggy on 10.7 (http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51906#c34),
+// so emulate recursive locking with a normal non-recursive mutex.
+#define RECURSIVE_CROSS_PROCESS_LOCK_INITIALIZER    \
+  { PTHREAD_MUTEX_INITIALIZER, 0, -1 }
+
+}  // namespace rlz_lib
+
+#endif  // RLZ_LIB_RECURSIVE_CROSS_PROCESS_LOCK_POSIX_H_