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      1 // Copyright (c) 2011 The Chromium 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 #include "base/synchronization/waitable_event.h"
      6 
      7 #include <math.h>
      8 #include <windows.h>
      9 
     10 #include "base/logging.h"
     11 #include "base/threading/thread_restrictions.h"
     12 #include "base/time/time.h"
     13 
     14 namespace base {
     15 
     16 WaitableEvent::WaitableEvent(bool manual_reset, bool signaled)
     17     : handle_(CreateEvent(NULL, manual_reset, signaled, NULL)) {
     18   // We're probably going to crash anyways if this is ever NULL, so we might as
     19   // well make our stack reports more informative by crashing here.
     20   CHECK(handle_.IsValid());
     21 }
     22 
     23 WaitableEvent::WaitableEvent(HANDLE handle)
     24     : handle_(handle) {
     25   CHECK(handle_.IsValid()) << "Tried to create WaitableEvent from NULL handle";
     26 }
     27 
     28 WaitableEvent::~WaitableEvent() {
     29 }
     30 
     31 HANDLE WaitableEvent::Release() {
     32   return handle_.Take();
     33 }
     34 
     35 void WaitableEvent::Reset() {
     36   ResetEvent(handle_.Get());
     37 }
     38 
     39 void WaitableEvent::Signal() {
     40   SetEvent(handle_.Get());
     41 }
     42 
     43 bool WaitableEvent::IsSignaled() {
     44   return TimedWait(TimeDelta::FromMilliseconds(0));
     45 }
     46 
     47 void WaitableEvent::Wait() {
     48   base::ThreadRestrictions::AssertWaitAllowed();
     49   DWORD result = WaitForSingleObject(handle_.Get(), INFINITE);
     50   // It is most unexpected that this should ever fail.  Help consumers learn
     51   // about it if it should ever fail.
     52   DCHECK_EQ(WAIT_OBJECT_0, result) << "WaitForSingleObject failed";
     53 }
     54 
     55 bool WaitableEvent::TimedWait(const TimeDelta& max_time) {
     56   base::ThreadRestrictions::AssertWaitAllowed();
     57   DCHECK(max_time >= TimeDelta::FromMicroseconds(0));
     58   // Be careful here.  TimeDelta has a precision of microseconds, but this API
     59   // is in milliseconds.  If there are 5.5ms left, should the delay be 5 or 6?
     60   // It should be 6 to avoid returning too early.
     61   double timeout = ceil(max_time.InMillisecondsF());
     62   DWORD result = WaitForSingleObject(handle_.Get(),
     63                                      static_cast<DWORD>(timeout));
     64   switch (result) {
     65     case WAIT_OBJECT_0:
     66       return true;
     67     case WAIT_TIMEOUT:
     68       return false;
     69   }
     70   // It is most unexpected that this should ever fail.  Help consumers learn
     71   // about it if it should ever fail.
     72   NOTREACHED() << "WaitForSingleObject failed";
     73   return false;
     74 }
     75 
     76 // static
     77 size_t WaitableEvent::WaitMany(WaitableEvent** events, size_t count) {
     78   base::ThreadRestrictions::AssertWaitAllowed();
     79   HANDLE handles[MAXIMUM_WAIT_OBJECTS];
     80   CHECK_LE(count, MAXIMUM_WAIT_OBJECTS)
     81       << "Can only wait on " << MAXIMUM_WAIT_OBJECTS << " with WaitMany";
     82 
     83   for (size_t i = 0; i < count; ++i)
     84     handles[i] = events[i]->handle();
     85 
     86   // The cast is safe because count is small - see the CHECK above.
     87   DWORD result =
     88       WaitForMultipleObjects(static_cast<DWORD>(count),
     89                              handles,
     90                              FALSE,      // don't wait for all the objects
     91                              INFINITE);  // no timeout
     92   if (result >= WAIT_OBJECT_0 + count) {
     93     DPLOG(FATAL) << "WaitForMultipleObjects failed";
     94     return 0;
     95   }
     96 
     97   return result - WAIT_OBJECT_0;
     98 }
     99 
    100 }  // namespace base
    101