base/message_pump_default.cc

// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "base/message_pump_default.h"

#include "base/logging.h"

namespace base {

MessagePumpDefault::MessagePumpDefault()
    : keep_running_(true),
      event_(false, false) {
}

void MessagePumpDefault::Run(Delegate* delegate) {
  DCHECK(keep_running_) << "Quit must have been called outside of Run!";

  for (;;) {
    bool did_work = delegate->DoWork();
    if (!keep_running_)
      break;
    if (did_work)
      continue;

    // TODO(darin): Delayed work will be starved if DoWork continues to return
    // true.  We should devise a better strategy.
    //
    // It is tempting to call DoWork followed by DoDelayedWork before checking
    // did_work, but we need to make sure that any tasks that were dispatched
    // prior to a timer actually run before the timer.  Getting that right may
    // require some additional changes.

    did_work = delegate->DoDelayedWork(&delayed_work_time_);
    if (!keep_running_)
      break;
    if (did_work)
      continue;

    did_work = delegate->DoIdleWork();
    if (!keep_running_)
      break;
    if (did_work)
      continue;

    if (delayed_work_time_.is_null()) {
      event_.Wait();
    } else {
      TimeDelta delay = delayed_work_time_ - Time::Now();
      if (delay > TimeDelta()) {
        event_.TimedWait(delay);
      } else {
        // It looks like delayed_work_time_ indicates a time in the past, so we
        // need to call DoDelayedWork now.
        delayed_work_time_ = Time();
      }
    }
    // Since event_ is auto-reset, we don't need to do anything special here
    // other than service each delegate method.
  }

  keep_running_ = true;
}

void MessagePumpDefault::Quit() {
  keep_running_ = false;
}

void MessagePumpDefault::ScheduleWork() {
  // Since this can be called on any thread, we need to ensure that our Run
  // loop wakes up.
  event_.Signal();
}

void MessagePumpDefault::ScheduleDelayedWork(const Time& delayed_work_time) {
  // We know that we can't be blocked on Wait right now since this method can
  // only be called on the same thread as Run, so we only need to update our
  // record of how long to sleep when we do sleep.
  delayed_work_time_ = delayed_work_time;
}

}  // namespace base