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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: */
/* 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 nsMemoryPressure_h__
#define nsMemoryPressure_h__

#include "nscore.h"

enum MemoryPressureState {
  /*
   * No memory pressure.
   */
  MemPressure_None = 0,

  /*
   * New memory pressure deteced.
   *
   * On a new memory pressure, we stop everything to start cleaning
   * aggresively the memory used, in order to free as much memory as
   * possible.
   */
  MemPressure_New,

  /*
   * Repeated memory pressure.
   *
   * A repeated memory pressure implies to clean softly recent allocations.
   * It is supposed to happen after a new memory pressure which already
   * cleaned aggressivley.  So there is no need to damage the reactivity of
   * Gecko by stopping the world again.
   *
   * In case of conflict with an new memory pressue, the new memory pressure
   * takes precedence over an ongoing memory pressure.  The reason being
   * that if no events are processed between 2 notifications (new followed
   * by ongoing, or ongoing followed by a new) we want to be as aggresive as
   * possible on the clean-up of the memory.  After all, we are trying to
   * keep Gecko alive as long as possible.
   */
  MemPressure_Ongoing,

  /*
   * Memory pressure stopped.
   *
   * We're no longer under acute memory pressure, so we might want to have a
   * chance of (cautiously) re-enabling some things we previously turned off.
   * As above, an already enqueued new memory pressure event takes precedence.
   * The priority ordering between concurrent attempts to queue both stopped
   * and ongoing memory pressure is currently not defined.
   */
  MemPressure_Stopping
};

/**
 * Return and erase the latest state of the memory pressure event set by any of
 * the corresponding dispatch functions.
 *
 * This is called when processing events on the main thread to check whether to
 * fire a memory pressure notification.
 */
MemoryPressureState NS_GetPendingMemoryPressure();

/**
 * This function causes the main thread to fire a memory pressure event
 * before processing the next event, but if there are no events pending in
 * the main thread's event queue, the memory pressure event would not be
 * dispatched until one is enqueued. It is infallible and does not allocate
 * any memory.
 *
 * You may call this function from any thread.
 */
void NS_DispatchEventualMemoryPressure(MemoryPressureState aState);

/**
 * This function causes the main thread to fire a memory pressure event
 * before processing the next event. We wake up the main thread by adding a
 * dummy event to its event loop, so, unlike with
 * NS_DispatchEventualMemoryPressure, this memory-pressure event is always
 * fired relatively quickly, even if the event loop is otherwise empty.
 *
 * You may call this function from any thread.
 */
nsresult NS_DispatchMemoryPressure(MemoryPressureState aState);

#endif  // nsMemoryPressure_h__