client/base/synchronization/waitable_event_win.cc

/*
  Copyright 2014 Google Inc.

  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
*/

#include <windows.h>
#include <math.h>

#include "base/logging.h"
#include "base/time.h"
#include "base/synchronization/waitable_event.h"


namespace base {

WaitableEvent::WaitableEvent(bool manual_reset, bool signaled)
    : handle_(CreateEvent(NULL, manual_reset, signaled, NULL)) {
  // We're probably going to crash anyways if this is ever NULL, so we might as
  // well make our stack reports more informative by crashing here.
  DCHECK(handle_);
}

WaitableEvent::WaitableEvent(HANDLE handle)
    : handle_(handle) {
  DCHECK(handle) << "Tried to create WaitableEvent from NULL handle";
}

WaitableEvent::~WaitableEvent() {
  CloseHandle(handle_);
}

HANDLE WaitableEvent::Release() {
  HANDLE rv = handle_;
  handle_ = INVALID_HANDLE_VALUE;
  return rv;
}

void WaitableEvent::Reset() {
  ResetEvent(handle_);
}

void WaitableEvent::Signal() {
  SetEvent(handle_);
}

bool WaitableEvent::IsSignaled() {
  return TimedWait(TimeDelta::FromMilliseconds(0));
}

bool WaitableEvent::Wait() {
  DWORD result = WaitForSingleObject(handle_, INFINITE);
  // It is most unexpected that this should ever fail.  Help consumers learn
  // about it if it should ever fail.
  DCHECK(result == WAIT_OBJECT_0) << "WaitForSingleObject failed";
  return result == WAIT_OBJECT_0;
}

bool WaitableEvent::TimedWait(const TimeDelta& max_time) {
  DCHECK(max_time >= TimeDelta::FromMicroseconds(0));
  // Be careful here.  TimeDelta has a precision of microseconds, but this API
  // is in milliseconds.  If there are 5.5ms left, should the delay be 5 or 6?
  // It should be 6 to avoid returning too early.
  double timeout = ceil(max_time.InMillisecondsF());
  DWORD result = WaitForSingleObject(handle_, static_cast<DWORD>(timeout));
  switch (result) {
    case WAIT_OBJECT_0:
      return true;
    case WAIT_TIMEOUT:
      return false;
  }
  // It is most unexpected that this should ever fail.  Help consumers learn
  // about it if it should ever fail.
  NOTREACHED() << "WaitForSingleObject failed";
  return false;
}

// static
size_t WaitableEvent::WaitMany(WaitableEvent** events, size_t count) {
  HANDLE handles[MAXIMUM_WAIT_OBJECTS];
  DCHECK_LE(count, MAXIMUM_WAIT_OBJECTS)
      << "Can only wait on " << MAXIMUM_WAIT_OBJECTS << " with WaitMany";

  for (size_t i = 0; i < count; ++i)
    handles[i] = events[i]->handle();

  // The cast is safe because count is small - see the CHECK above.
  DWORD result =
      WaitForMultipleObjects(static_cast<DWORD>(count),
                             handles,
                             FALSE,      // don't wait for all the objects
                             INFINITE);  // no timeout
  if (result >= WAIT_OBJECT_0 + count) {
    NOTREACHED() << "WaitForMultipleObjects failed: " << GetLastError();
    return 0;
  }

  return result - WAIT_OBJECT_0;
}

}  // namespace base