Quelle nsMemoryPressure.h Sprache: C

/* -*- 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"

/*
* These pre-defined strings are the topic to pass to the observer
* service to declare the memory-pressure or lift the memory-pressure.
*
* 1. Notify kTopicMemoryPressure with kSubTopicLowMemoryNew
* 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.
*
* 2. Notify kTopicMemoryPressure with kSubTopicLowMemoryOngoing
* 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.
*
* 3. Notify kTopicMemoryPressureStop with nullptr
* 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.
*/
extern const char* const kTopicMemoryPressure;
extern const char* const kTopicMemoryPressureStop;
extern const char16_t* const kSubTopicLowMemoryNew;
extern const char16_t* const kSubTopicLowMemoryOngoing;

enum class MemoryPressureState : uint32_t {
  None,  // For internal use.  Don't use this value.
  LowMemory,
  NoPressure,
};

/**
* 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_NotifyOfEventualMemoryPressure(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_NotifyOfEventualMemoryPressure, 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_NotifyOfMemoryPressure(MemoryPressureState aState);

#endif  // nsMemoryPressure_h__

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