1 // Copyright 2013 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 // MemoryPressure provides static APIs for handling memory pressure on 6 // platforms that have such signals, such as Android. 7 // The app will try to discard buffers that aren't deemed essential (individual 8 // modules will implement their own policy). 9 // 10 // Refer to memory_pressure_level_list.h for information about what sorts of 11 // signals can be sent under what conditions. 12 13 #ifndef BASE_MEMORY_PRESSURE_LISTENER_H_ 14 #define BASE_MEMORY_PRESSURE_LISTENER_H_ 15 16 #include "base/base_export.h" 17 #include "base/basictypes.h" 18 #include "base/callback.h" 19 20 namespace base { 21 22 // To start listening, create a new instance, passing a callback to a 23 // function that takes a MemoryPressureLevel parameter. To stop listening, 24 // simply delete the listener object. The implementation guarantees 25 // that the callback will always be called on the thread that created 26 // the listener. 27 // If this is the same thread as the system is broadcasting the memory pressure 28 // event on, then it is guaranteed you're called synchronously within that 29 // broadcast and hence you should not do long-running garbage collection work. 30 // But conversely, if there's something that needs to be released before 31 // control is returned to system code, this is the place to do it. 32 // Please see notes on memory_pressure_level_list.h: some levels are absolutely 33 // critical, and if not enough memory is returned to the system, it'll 34 // potentially kill the app, and then later the app will have to be 35 // cold-started. 36 // 37 // 38 // Example: 39 // 40 // void OnMemoryPressure(MemoryPressureLevel memory_pressure_level) { 41 // ... 42 // } 43 // 44 // // Start listening. 45 // MemoryPressureListener* my_listener = 46 // new MemoryPressureListener(base::Bind(&OnMemoryPressure)); 47 // 48 // ... 49 // 50 // // Stop listening. 51 // delete my_listener; 52 // 53 class BASE_EXPORT MemoryPressureListener { 54 public: 55 enum MemoryPressureLevel { 56 #define DEFINE_MEMORY_PRESSURE_LEVEL(name, value) name = value, 57 #include "base/memory/memory_pressure_level_list.h" 58 #undef DEFINE_MEMORY_PRESSURE_LEVEL 59 }; 60 61 typedef base::Callback<void(MemoryPressureLevel)> MemoryPressureCallback; 62 63 explicit MemoryPressureListener( 64 const MemoryPressureCallback& memory_pressure_callback); 65 ~MemoryPressureListener(); 66 67 // Intended for use by the platform specific implementation. 68 static void NotifyMemoryPressure(MemoryPressureLevel memory_pressure_level); 69 70 private: 71 void Notify(MemoryPressureLevel memory_pressure_level); 72 73 MemoryPressureCallback callback_; 74 75 DISALLOW_COPY_AND_ASSIGN(MemoryPressureListener); 76 }; 77 78 } // namespace base 79 80 #endif // BASE_MEMORY_PRESSURE_LISTENER_H_ 81
