Simplify implementation of Mutex.

src/mutex.h

+// Copyright 2013 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef V8_MUTEX_H_
+#define V8_MUTEX_H_
+
+#include "globals.h"
+
+#if V8_OS_UNIX
+#include <pthread.h>  // NOLINT
+#elif V8_OS_WIN32
+#include "win32-headers.h"
+#endif
+
+#include "checks.h"
+#include "lazy-instance.h"
+
+namespace v8 {
+namespace internal {
+
+// ----------------------------------------------------------------------------
+// Mutex
+//
+// Mutexes are used for serializing access to non-reentrant sections of code.
+// The implementations of mutex should allow for nested/recursive locking.
+//
+class Mutex {
+ public:
+  Mutex();
+  ~Mutex();
+
+  // Locks the given mutex. If the mutex is currently unlocked, it becomes
+  // locked and owned by the calling thread. If the mutex is already locked
+  // by another thread, suspends the calling thread until the mutex is
+  // unlocked.
+  void Lock();
+
+  // Unlocks the given mutex. The mutex is assumed to be locked and owned
+  // by the calling thread on entrance.
+  void Unlock();
+
+  // Tries to lock the given mutex. Returns true if the mutex was locked
+  // successfully.
+  bool TryLock();
+
+ private:
+#if V8_OS_UNIX
+  pthread_mutex_t mutex_;
+#elif V8_OS_WIN32
+  CRITICAL_SECTION cs_;
+#endif
+
+  DISALLOW_COPY_AND_ASSIGN(Mutex);
+};
+
+
+// ----------------------------------------------------------------------------
+// LazyMutex
+//
+// POD Mutex initialized lazily (i.e. the first time Pointer() is called).
+// Usage:
+//   static LazyMutex my_mutex = LAZY_MUTEX_INITIALIZER;
+//
+//   void my_function() {
+//     ScopedLock my_lock(&my_mutex);
+//     // Do something.
+//   }
+//
+typedef LazyDynamicInstance<Mutex,
+                            DefaultCreateTrait<Mutex>,
+                            ThreadSafeInitOnceTrait>::type LazyMutex;
+
+#define LAZY_MUTEX_INITIALIZER LAZY_DYNAMIC_INSTANCE_INITIALIZER
+
+
+// ----------------------------------------------------------------------------
+// ScopedLock
+//
+// Stack-allocated ScopedLocks provide block-scoped locking and
+// unlocking of a mutex.
+//
+class ScopedLock {

[Sven Panne, 2013/07/30 15:09:56]

It would be cool if we could restrict the usage of Mutexes to this class, i.e.
without public Lock/Unlock methods, but I guess we are not really there yet...

[Benedikt Meurer, 2013/07/30 16:50:52]

Not yet, unfortunately...

+ public:
+  explicit ScopedLock(Mutex* mutex): mutex_(mutex) {
+    ASSERT(mutex_ != NULL);
+    mutex_->Lock();
+  }
+
+  explicit ScopedLock(LazyMutex* lazy_mutex) : mutex_(lazy_mutex->Pointer()) {
+    ASSERT(mutex_ != NULL);
+    mutex_->Lock();
+  }
+
+  ~ScopedLock() {
+    mutex_->Unlock();
+  }
+
+ private:
+  Mutex* mutex_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedLock);
+};
+
+} }  // namespace v8::internal
+
+#endif  // V8_MUTEX_H_