1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ 2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */ 3 /* This Source Code Form is subject to the terms of the Mozilla Public 4 * License, v. 2.0. If a copy of the MPL was not distributed with this 5 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ 6 7 #ifndef nsMemoryPressure_h__ 8 #define nsMemoryPressure_h__ 9 10 #include "nscore.h" 11 12 /* 13 * These pre-defined strings are the topic to pass to the observer 14 * service to declare the memory-pressure or lift the memory-pressure. 15 * 16 * 1. Notify kTopicMemoryPressure with kSubTopicLowMemoryNew 17 * New memory pressure deteced 18 * On a new memory pressure, we stop everything to start cleaning 19 * aggresively the memory used, in order to free as much memory as 20 * possible. 21 * 22 * 2. Notify kTopicMemoryPressure with kSubTopicLowMemoryOngoing 23 * Repeated memory pressure. 24 * A repeated memory pressure implies to clean softly recent allocations. 25 * It is supposed to happen after a new memory pressure which already 26 * cleaned aggressivley. So there is no need to damage the reactivity of 27 * Gecko by stopping the world again. 28 * 29 * In case of conflict with an new memory pressue, the new memory pressure 30 * takes precedence over an ongoing memory pressure. The reason being 31 * that if no events are processed between 2 notifications (new followed 32 * by ongoing, or ongoing followed by a new) we want to be as aggresive as 33 * possible on the clean-up of the memory. After all, we are trying to 34 * keep Gecko alive as long as possible. 35 * 36 * 3. Notify kTopicMemoryPressureStop with nullptr 37 * Memory pressure stopped. 38 * We're no longer under acute memory pressure, so we might want to have a 39 * chance of (cautiously) re-enabling some things we previously turned off. 40 * As above, an already enqueued new memory pressure event takes precedence. 41 * The priority ordering between concurrent attempts to queue both stopped 42 * and ongoing memory pressure is currently not defined. 43 */ 44 extern const char* const kTopicMemoryPressure; 45 extern const char* const kTopicMemoryPressureStop; 46 extern const char16_t* const kSubTopicLowMemoryNew; 47 extern const char16_t* const kSubTopicLowMemoryOngoing; 48 49 enum class MemoryPressureState : uint32_t { 50 None, // For internal use. Don't use this value. 51 LowMemory, 52 NoPressure, 53 }; 54 55 /** 56 * This function causes the main thread to fire a memory pressure event 57 * before processing the next event, but if there are no events pending in 58 * the main thread's event queue, the memory pressure event would not be 59 * dispatched until one is enqueued. It is infallible and does not allocate 60 * any memory. 61 * 62 * You may call this function from any thread. 63 */ 64 void NS_NotifyOfEventualMemoryPressure(MemoryPressureState aState); 65 66 /** 67 * This function causes the main thread to fire a memory pressure event 68 * before processing the next event. We wake up the main thread by adding a 69 * dummy event to its event loop, so, unlike with 70 * NS_NotifyOfEventualMemoryPressure, this memory-pressure event is always 71 * fired relatively quickly, even if the event loop is otherwise empty. 72 * 73 * You may call this function from any thread. 74 */ 75 nsresult NS_NotifyOfMemoryPressure(MemoryPressureState aState); 76 77 #endif // nsMemoryPressure_h__ 78