File: message_pump_qt.cc

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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
// Copyright (c) 2010 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 <qabstracteventdispatcher.h>
#include <qevent.h>
#include <QCoreApplication>
#include <QThread>
#include <qtimer.h>

#include "base/message_pump_qt.h"

#include <fcntl.h>
#include <limits>
#include <math.h>

#include "base/eintr_wrapper.h"
#include "base/logging.h"
#include "base/platform_thread.h"

namespace {
// Cached QEvent user type, registered for our event system
static int sPokeEvent;
}  // namespace

namespace base {

MessagePumpForUI::MessagePumpForUI()
  : state_(NULL),
    qt_pump(*this)
{
}

MessagePumpForUI::~MessagePumpForUI() {
}

MessagePumpQt::MessagePumpQt(MessagePumpForUI &aPump)
  : pump(aPump), mTimer(new QTimer(this))
{
  // Register our custom event type, to use in qApp event loop
  sPokeEvent = QEvent::registerEventType();
  connect(mTimer, SIGNAL(timeout()), this, SLOT(dispatchDelayed()));
  mTimer->setSingleShot(true);
}

MessagePumpQt::~MessagePumpQt()
{
  mTimer->stop();
  delete mTimer;
}

bool
MessagePumpQt::event(QEvent *e)
{
  if (e->type() == sPokeEvent) {
    pump.HandleDispatch();
    return true;
  }
  return false;
}

void
MessagePumpQt::scheduleDelayedIfNeeded(const TimeTicks& delayed_work_time)
{
  if (delayed_work_time.is_null()) {
    return;
  }

  if (mTimer->isActive()) {
    mTimer->stop();
  }

  TimeDelta later = delayed_work_time - TimeTicks::Now();
  // later.InMilliseconds() returns an int64_t, QTimer only accepts int's for start(),
  // std::min only works on exact same types.
  int laterMsecs = later.InMilliseconds() > std::numeric_limits<int>::max() ?
    std::numeric_limits<int>::max() : later.InMilliseconds();
  mTimer->start(laterMsecs > 0 ? laterMsecs : 0);
}

void
MessagePumpQt::dispatchDelayed()
{
  pump.HandleDispatch();
}

void MessagePumpForUI::Run(Delegate* delegate) {
  RunState state;
  state.delegate = delegate;
  state.should_quit = false;
  state.run_depth = state_ ? state_->run_depth + 1 : 1;
  // We really only do a single task for each iteration of the loop.  If we
  // have done something, assume there is likely something more to do.  This
  // will mean that we don't block on the message pump until there was nothing
  // more to do.  We also set this to true to make sure not to block on the
  // first iteration of the loop, so RunAllPending() works correctly.
  bool more_work_is_plausible = true;

  RunState* previous_state = state_;
  state_ = &state;

  for(;;) {
    QEventLoop::ProcessEventsFlags block = QEventLoop::AllEvents;
    if (!more_work_is_plausible) {
      block |= QEventLoop::WaitForMoreEvents;
    }

    QAbstractEventDispatcher* dispatcher =
      QAbstractEventDispatcher::instance(QThread::currentThread());
    // An assertion seems too much here, as during startup,
    // the dispatcher might not be ready yet.
    if (!dispatcher) {
      return;
    }

    // processEvent's returns true if an event has been processed.
    more_work_is_plausible = dispatcher->processEvents(block);

    if (state_->should_quit) {
      break;
    }

    more_work_is_plausible |= state_->delegate->DoWork();
    if (state_->should_quit) {
      break;
    }

    more_work_is_plausible |=
      state_->delegate->DoDelayedWork(&delayed_work_time_);
    if (state_->should_quit) {
      break;
    }

    qt_pump.scheduleDelayedIfNeeded(delayed_work_time_);

    if (more_work_is_plausible) {
      continue;
    }

    more_work_is_plausible = state_->delegate->DoIdleWork();
    if (state_->should_quit) {
      break;
    }
  }

  state_ = previous_state;
}

void MessagePumpForUI::HandleDispatch() {
  if (state_->should_quit) {
    return;
  }

  if (state_->delegate->DoWork()) {
    // there might be more, see more_work_is_plausible 
    // variable above, that's why we ScheduleWork() to keep going.
    ScheduleWork();
  }

  if (state_->should_quit) {
    return;
  }

  state_->delegate->DoDelayedWork(&delayed_work_time_);
  qt_pump.scheduleDelayedIfNeeded(delayed_work_time_);
}

void MessagePumpForUI::Quit() {
  if (state_) {
    state_->should_quit = true;
  } else {
    NOTREACHED() << "Quit called outside Run!";
  }
}

void MessagePumpForUI::ScheduleWork() {
  QCoreApplication::postEvent(&qt_pump,
                              new QEvent((QEvent::Type) sPokeEvent));
}

void MessagePumpForUI::ScheduleDelayedWork(const TimeTicks& delayed_work_time) {
  // On GLib implementation, a work source is defined which explicitly checks the
  // time that has passed. Here, on Qt we can use a QTimer that enqueues our
  // event signal in an event queue.
  delayed_work_time_ = delayed_work_time;
  qt_pump.scheduleDelayedIfNeeded(delayed_work_time_);
}

}  // namespace base