| // Copyright 2016 The Chromium Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #ifndef BASE_MEMORY_MEMORY_COORDINATOR_CLIENT_H_ |
| #define BASE_MEMORY_MEMORY_COORDINATOR_CLIENT_H_ |
| |
| #include "base/base_export.h" |
| |
| namespace base { |
| |
| // OVERVIEW: |
| // |
| // MemoryCoordinatorClient is an interface which a component can implement to |
| // adjust "future allocation" and "existing allocation". For "future allocation" |
| // it provides a callback to observe memory state changes, and for "existing |
| // allocation" it provides a callback to purge memory. |
| // |
| // Unlike MemoryPressureListener, memory state changes are stateful. State |
| // transitions are throttled to avoid thrashing; the exact throttling period is |
| // platform dependent, but will be at least 5-10 seconds. When a state change |
| // notification is dispatched, clients are expected to update their allocation |
| // policies (e.g. setting cache limit) that persist for the duration of the |
| // memory state. Note that clients aren't expected to free up memory on memory |
| // state changes. Clients should wait for a separate purge request to free up |
| // memory. Purging requests will be throttled as well. |
| |
| // MemoryState is an indicator that processes can use to guide their memory |
| // allocation policies. For example, a process that receives the throttled |
| // state can use that as as signal to decrease memory cache limits. |
| // NOTE: This enum is used to back an UMA histogram, and therefore should be |
| // treated as append-only. |
| enum class MemoryState : int { |
| // The state is unknown. |
| UNKNOWN = -1, |
| // No memory constraints. |
| NORMAL = 0, |
| // Running and interactive but memory allocation should be throttled. |
| // Clients should set lower budget for any memory that is used as an |
| // optimization but that is not necessary for the process to run. |
| // (e.g. caches) |
| THROTTLED = 1, |
| // Still resident in memory but core processing logic has been suspended. |
| // In most cases, OnPurgeMemory() will be called before entering this state. |
| SUSPENDED = 2, |
| }; |
| |
| const int kMemoryStateMax = static_cast<int>(MemoryState::SUSPENDED) + 1; |
| |
| // Returns a string representation of MemoryState. |
| BASE_EXPORT const char* MemoryStateToString(MemoryState state); |
| |
| // This is an interface for components which can respond to memory status |
| // changes. An initial state is NORMAL. See MemoryCoordinatorClientRegistry for |
| // threading guarantees and ownership management. |
| class BASE_EXPORT MemoryCoordinatorClient { |
| public: |
| // Called when memory state has changed. Any transition can occur except for |
| // UNKNOWN. General guidelines are: |
| // * NORMAL: Restore the default settings for memory allocation/usage if |
| // it has changed. |
| // * THROTTLED: Use smaller limits for future memory allocations. You don't |
| // need to take any action on existing allocations. |
| // * SUSPENDED: Use much smaller limits for future memory allocations. You |
| // don't need to take any action on existing allocations. |
| virtual void OnMemoryStateChange(MemoryState state) {} |
| |
| // Called to purge memory. |
| // This callback should free up any memory that is used as an optimization, or |
| // any memory whose contents can be reproduced. |
| virtual void OnPurgeMemory() {} |
| |
| protected: |
| virtual ~MemoryCoordinatorClient() = default; |
| }; |
| |
| } // namespace base |
| |
| #endif // BASE_MEMORY_MEMORY_COORDINATOR_CLIENT_H_ |