michael@0: // Copyright (c) 2011 The Chromium Authors. All rights reserved.
michael@0: // Use of this source code is governed by a BSD-style license that can be
michael@0: // found in the LICENSE file.
michael@0: 
michael@0: #ifndef BASE_SYNCHRONIZATION_LOCK_H_
michael@0: #define BASE_SYNCHRONIZATION_LOCK_H_
michael@0: 
michael@0: #include "base/base_export.h"
michael@0: #include "base/synchronization/lock_impl.h"
michael@0: #include "base/threading/platform_thread.h"
michael@0: 
michael@0: namespace base {
michael@0: 
michael@0: // A convenient wrapper for an OS specific critical section.  The only real
michael@0: // intelligence in this class is in debug mode for the support for the
michael@0: // AssertAcquired() method.
michael@0: class BASE_EXPORT Lock {
michael@0:  public:
michael@0: #if defined(NDEBUG)             // Optimized wrapper implementation
michael@0:   Lock() : lock_() {}
michael@0:   ~Lock() {}
michael@0:   void Acquire() { lock_.Lock(); }
michael@0:   void Release() { lock_.Unlock(); }
michael@0: 
michael@0:   // If the lock is not held, take it and return true. If the lock is already
michael@0:   // held by another thread, immediately return false. This must not be called
michael@0:   // by a thread already holding the lock (what happens is undefined and an
michael@0:   // assertion may fail).
michael@0:   bool Try() { return lock_.Try(); }
michael@0: 
michael@0:   // Null implementation if not debug.
michael@0:   void AssertAcquired() const {}
michael@0: #else
michael@0:   Lock();
michael@0:   ~Lock();
michael@0: 
michael@0:   // NOTE: Although windows critical sections support recursive locks, we do not
michael@0:   // allow this, and we will commonly fire a DCHECK() if a thread attempts to
michael@0:   // acquire the lock a second time (while already holding it).
michael@0:   void Acquire() {
michael@0:     lock_.Lock();
michael@0:     CheckUnheldAndMark();
michael@0:   }
michael@0:   void Release() {
michael@0:     CheckHeldAndUnmark();
michael@0:     lock_.Unlock();
michael@0:   }
michael@0: 
michael@0:   bool Try() {
michael@0:     bool rv = lock_.Try();
michael@0:     if (rv) {
michael@0:       CheckUnheldAndMark();
michael@0:     }
michael@0:     return rv;
michael@0:   }
michael@0: 
michael@0:   void AssertAcquired() const;
michael@0: #endif                          // NDEBUG
michael@0: 
michael@0: #if defined(OS_POSIX)
michael@0:   // The posix implementation of ConditionVariable needs to be able
michael@0:   // to see our lock and tweak our debugging counters, as it releases
michael@0:   // and acquires locks inside of pthread_cond_{timed,}wait.
michael@0:   friend class ConditionVariable;
michael@0: #elif defined(OS_WIN)
michael@0:   // The Windows Vista implementation of ConditionVariable needs the
michael@0:   // native handle of the critical section.
michael@0:   friend class WinVistaCondVar;
michael@0: #endif
michael@0: 
michael@0:  private:
michael@0: #if !defined(NDEBUG)
michael@0:   // Members and routines taking care of locks assertions.
michael@0:   // Note that this checks for recursive locks and allows them
michael@0:   // if the variable is set.  This is allowed by the underlying implementation
michael@0:   // on windows but not on Posix, so we're doing unneeded checks on Posix.
michael@0:   // It's worth it to share the code.
michael@0:   void CheckHeldAndUnmark();
michael@0:   void CheckUnheldAndMark();
michael@0: 
michael@0:   // All private data is implicitly protected by lock_.
michael@0:   // Be VERY careful to only access members under that lock.
michael@0: 
michael@0:   // Determines validity of owning_thread_id_.  Needed as we don't have
michael@0:   // a null owning_thread_id_ value.
michael@0:   bool owned_by_thread_;
michael@0:   base::PlatformThreadId owning_thread_id_;
michael@0: #endif  // NDEBUG
michael@0: 
michael@0:   // Platform specific underlying lock implementation.
michael@0:   internal::LockImpl lock_;
michael@0: 
michael@0:   DISALLOW_COPY_AND_ASSIGN(Lock);
michael@0: };
michael@0: 
michael@0: // A helper class that acquires the given Lock while the AutoLock is in scope.
michael@0: class AutoLock {
michael@0:  public:
michael@0:   struct AlreadyAcquired {};
michael@0: 
michael@0:   explicit AutoLock(Lock& lock) : lock_(lock) {
michael@0:     lock_.Acquire();
michael@0:   }
michael@0: 
michael@0:   AutoLock(Lock& lock, const AlreadyAcquired&) : lock_(lock) {
michael@0:     lock_.AssertAcquired();
michael@0:   }
michael@0: 
michael@0:   ~AutoLock() {
michael@0:     lock_.AssertAcquired();
michael@0:     lock_.Release();
michael@0:   }
michael@0: 
michael@0:  private:
michael@0:   Lock& lock_;
michael@0:   DISALLOW_COPY_AND_ASSIGN(AutoLock);
michael@0: };
michael@0: 
michael@0: // AutoUnlock is a helper that will Release() the |lock| argument in the
michael@0: // constructor, and re-Acquire() it in the destructor.
michael@0: class AutoUnlock {
michael@0:  public:
michael@0:   explicit AutoUnlock(Lock& lock) : lock_(lock) {
michael@0:     // We require our caller to have the lock.
michael@0:     lock_.AssertAcquired();
michael@0:     lock_.Release();
michael@0:   }
michael@0: 
michael@0:   ~AutoUnlock() {
michael@0:     lock_.Acquire();
michael@0:   }
michael@0: 
michael@0:  private:
michael@0:   Lock& lock_;
michael@0:   DISALLOW_COPY_AND_ASSIGN(AutoUnlock);
michael@0: };
michael@0: 
michael@0: }  // namespace base
michael@0: 
michael@0: #endif  // BASE_SYNCHRONIZATION_LOCK_H_