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      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.
      4 
      5 #ifndef V8_BASE_PLATFORM_CONDITION_VARIABLE_H_
      6 #define V8_BASE_PLATFORM_CONDITION_VARIABLE_H_
      7 
      8 #include "src/base/lazy-instance.h"
      9 #include "src/base/platform/mutex.h"
     10 
     11 namespace v8 {
     12 namespace base {
     13 
     14 // Forward declarations.
     15 class ConditionVariableEvent;
     16 class TimeDelta;
     17 
     18 // -----------------------------------------------------------------------------
     19 // ConditionVariable
     20 //
     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.
     30 
     31 class ConditionVariable FINAL {
     32  public:
     33   ConditionVariable();
     34   ~ConditionVariable();
     35 
     36   // If any threads are waiting on this condition variable, calling
     37   // |NotifyOne()| unblocks one of the waiting threads.
     38   void NotifyOne();
     39 
     40   // Unblocks all threads currently waiting for this condition variable.
     41   void NotifyAll();
     42 
     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);
     51 
     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;
     60 
     61   // The implementation-defined native handle type.
     62 #if V8_OS_POSIX
     63   typedef pthread_cond_t NativeHandle;
     64 #elif V8_OS_WIN
     65   struct Event;
     66   class NativeHandle FINAL {
     67    public:
     68     NativeHandle() : waitlist_(NULL), freelist_(NULL) {}
     69     ~NativeHandle();
     70 
     71     Event* Pre() WARN_UNUSED_RESULT;
     72     void Post(Event* event, bool result);
     73 
     74     Mutex* mutex() { return &mutex_; }
     75     Event* waitlist() { return waitlist_; }
     76 
     77    private:
     78     Event* waitlist_;
     79     Event* freelist_;
     80     Mutex mutex_;
     81 
     82     DISALLOW_COPY_AND_ASSIGN(NativeHandle);
     83   };
     84 #endif
     85 
     86   NativeHandle& native_handle() {
     87     return native_handle_;
     88   }
     89   const NativeHandle& native_handle() const {
     90     return native_handle_;
     91   }
     92 
     93  private:
     94   NativeHandle native_handle_;
     95 
     96   DISALLOW_COPY_AND_ASSIGN(ConditionVariable);
     97 };
     98 
     99 
    100 // POD ConditionVariable initialized lazily (i.e. the first time Pointer() is
    101 // called).
    102 // Usage:
    103 //   static LazyConditionVariable my_condvar =
    104 //       LAZY_CONDITION_VARIABLE_INITIALIZER;
    105 //
    106 //   void my_function() {
    107 //     LockGuard<Mutex> lock_guard(&my_mutex);
    108 //     my_condvar.Pointer()->Wait(&my_mutex);
    109 //   }
    110 typedef LazyStaticInstance<
    111     ConditionVariable, DefaultConstructTrait<ConditionVariable>,
    112     ThreadSafeInitOnceTrait>::type LazyConditionVariable;
    113 
    114 #define LAZY_CONDITION_VARIABLE_INITIALIZER LAZY_STATIC_INSTANCE_INITIALIZER
    115 
    116 } }  // namespace v8::base
    117 
    118 #endif  // V8_BASE_PLATFORM_CONDITION_VARIABLE_H_
    119