gecko/gfx/layers/ipc/TaskThrottler.h

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/* -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil; tab-width: 2; -*- */
/* vim: set sw=4 ts=8 et tw=80 : */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#ifndef mozilla_dom_TaskThrottler_h
#define mozilla_dom_TaskThrottler_h
#include "nsAutoPtr.h"
class CancelableTask;
namespace tracked_objects {
class Location;
}
namespace mozilla {
namespace layers {
/** The TaskThrottler prevents update event overruns. It is used in cases where
* you're sending an async message and waiting for a reply. You need to call
* PostTask to queue a task and TaskComplete when you get a response.
*
* The call to TaskComplete will run the recent task posted since the last
* request was sent, if any. This means that at any time there can be at most 1
* outstanding request being processed and at most 1 queued behind it.
*
* This is used in the context of repainting a scrollable region. While another
* process is painting you might get several updates from the UI thread but when
* the paint is complete you want to send the most recent.
*/
class TaskThrottler {
public:
TaskThrottler();
/** Post a task to be run as soon as there are no outstanding tasks.
*
* @param aLocation Use the macro FROM_HERE
* @param aTask Ownership of this object is transferred to TaskThrottler
* which will delete it when it is either run or becomes
* obsolete or the TaskThrottler is destructed.
*/
void PostTask(const tracked_objects::Location& aLocation,
CancelableTask* aTask);
void TaskComplete();
private:
bool mOutstanding;
nsAutoPtr<CancelableTask> mQueuedTask;
};
}
}
#endif // mozilla_dom_TaskThrottler_h