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