blob: 804f0a6b8545a0f489a25a6aea5e4b463d024b2e [file] [log] [blame]
// 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.
#include "base/base_export.h"
namespace base {
// 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.
// No memory constraints.
// 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)
// Still resident in memory but core processing logic has been suspended.
// In most cases, OnPurgeMemory() will be called before entering this state.
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 {
// 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() {}
virtual ~MemoryCoordinatorClient() = default;
} // namespace base