1 // Copyright 2013 the V8 project authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
5 #ifndef V8_BASE_PLATFORM_CONDITION_VARIABLE_H_
6 #define V8_BASE_PLATFORM_CONDITION_VARIABLE_H_
8 #include "src/base/lazy-instance.h"
9 #include "src/base/platform/mutex.h"
14 // Forward declarations.
15 class ConditionVariableEvent;
18 // -----------------------------------------------------------------------------
21 // This class is a synchronization primitive that can be used to block a thread,
22 // or multiple threads at the same time, until:
23 // - a notification is received from another thread,
24 // - a timeout expires, or
25 // - a spurious wakeup occurs
26 // Any thread that intends to wait on a ConditionVariable has to acquire a lock
27 // on a Mutex first. The |Wait()| and |WaitFor()| operations atomically release
28 // the mutex and suspend the execution of the calling thread. When the condition
29 // variable is notified, the thread is awakened, and the mutex is reacquired.
31 class ConditionVariable final {
36 // If any threads are waiting on this condition variable, calling
37 // |NotifyOne()| unblocks one of the waiting threads.
40 // Unblocks all threads currently waiting for this condition variable.
43 // |Wait()| causes the calling thread to block until the condition variable is
44 // notified or a spurious wakeup occurs. Atomically releases the mutex, blocks
45 // the current executing thread, and adds it to the list of threads waiting on
46 // this condition variable. The thread will be unblocked when |NotifyAll()| or
47 // |NotifyOne()| is executed. It may also be unblocked spuriously. When
48 // unblocked, regardless of the reason, the lock on the mutex is reacquired
49 // and |Wait()| exits.
50 void Wait(Mutex* mutex);
52 // Atomically releases the mutex, blocks the current executing thread, and
53 // adds it to the list of threads waiting on this condition variable. The
54 // thread will be unblocked when |NotifyAll()| or |NotifyOne()| is executed,
55 // or when the relative timeout |rel_time| expires. It may also be unblocked
56 // spuriously. When unblocked, regardless of the reason, the lock on the mutex
57 // is reacquired and |WaitFor()| exits. Returns true if the condition variable
58 // was notified prior to the timeout.
59 bool WaitFor(Mutex* mutex, const TimeDelta& rel_time) WARN_UNUSED_RESULT;
61 // The implementation-defined native handle type.
63 typedef pthread_cond_t NativeHandle;
66 class NativeHandle final {
68 NativeHandle() : waitlist_(NULL), freelist_(NULL) {}
71 Event* Pre() WARN_UNUSED_RESULT;
72 void Post(Event* event, bool result);
74 Mutex* mutex() { return &mutex_; }
75 Event* waitlist() { return waitlist_; }
82 DISALLOW_COPY_AND_ASSIGN(NativeHandle);
86 NativeHandle& native_handle() {
87 return native_handle_;
89 const NativeHandle& native_handle() const {
90 return native_handle_;
94 NativeHandle native_handle_;
96 DISALLOW_COPY_AND_ASSIGN(ConditionVariable);
100 // POD ConditionVariable initialized lazily (i.e. the first time Pointer() is
103 // static LazyConditionVariable my_condvar =
104 // LAZY_CONDITION_VARIABLE_INITIALIZER;
106 // void my_function() {
107 // LockGuard<Mutex> lock_guard(&my_mutex);
108 // my_condvar.Pointer()->Wait(&my_mutex);
110 typedef LazyStaticInstance<
111 ConditionVariable, DefaultConstructTrait<ConditionVariable>,
112 ThreadSafeInitOnceTrait>::type LazyConditionVariable;
114 #define LAZY_CONDITION_VARIABLE_INITIALIZER LAZY_STATIC_INSTANCE_INITIALIZER
119 #endif // V8_BASE_PLATFORM_CONDITION_VARIABLE_H_