Drop the global memory state from memory coordinator

content/browser/memory/memory_state_updater.h

-// 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 CONTENT_BROWSER_MEMORY_MEMORY_STATE_UPDATER_H_
-#define CONTENT_BROWSER_MEMORY_MEMORY_STATE_UPDATER_H_
-
-#include "base/cancelable_callback.h"
-#include "base/single_thread_task_runner.h"
-#include "base/time/time.h"
-#include "content/browser/memory/memory_coordinator_impl.h"
-#include "content/common/content_export.h"
-
-namespace content {
-
-// MemoryStateUpdater is an internal implementation of MemoryCoordinator
-// which uses a heuristic to determine a single global memory state.
-// In the current implementation browser process and renderer processes share
-// the global state; the memory coordinator will notify the global state to
-// all background renderers if the state has changed.
-//
-// State calculation:
-// MemoryStateUpdater uses followings to determine the global state:
-// * Compute "number of renderers which can be created until the system will
-//   be in a critical state". Call this N.
-//   (See memory_monitor.h for the definition of "critical")
-// * Covert N to a memory state using some thresholds/hysteresis for each state.
-//   Once a state is changed to a limited state, larger N will be needed to go
-//   back to a relaxed state. (e.g. THROTTLED -> NORMAL)
-// * Once a state is changed, it remains the same for a certain period of time.
-class CONTENT_EXPORT MemoryStateUpdater {
- public:
-  // |coordinator| must outlive than this instance.
-  MemoryStateUpdater(MemoryCoordinatorImpl* coordinator,
-                     scoped_refptr<base::SingleThreadTaskRunner> task_runner);
-  ~MemoryStateUpdater();
-
-  // Calculates the next global state from the amount of free memory using
-  // a heuristic.
-  base::MemoryState CalculateNextState();
-
-  // Schedules a task to update the global state. The task will be executed
-  // after |delay| has passed.
-  void ScheduleUpdateState(base::TimeDelta delay);
-
- private:
-  FRIEND_TEST_ALL_PREFIXES(MemoryCoordinatorImplTest, CalculateNextState);
-  FRIEND_TEST_ALL_PREFIXES(MemoryCoordinatorImplTest, UpdateState);
-  FRIEND_TEST_ALL_PREFIXES(MemoryCoordinatorImplTest, SetMemoryStateForTesting);
-  FRIEND_TEST_ALL_PREFIXES(MemoryCoordinatorImplTest, ForceSetGlobalState);
-
-  // Periodically called to update the global state.
-  void UpdateState();
-
-  MemoryCoordinatorImpl* coordinator_;
-  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
-  base::CancelableClosure update_state_closure_;
-
-  // Sets up parameters for the heuristic.
-  void InitializeParameters();
-
-  // Validates parameters defined below.
-  bool ValidateParameters();
-
-  // Parameters to control the heuristic.
-
-  // The median size of a renderer on the current platform. This is used to
-  // convert the amount of free memory to an expected number of new renderers
-  // that could be started before hitting critical memory pressure.
-  int expected_renderer_size_;
-  // When in a NORMAL state and the potential number of new renderers drops
-  // below this level, the coordinator will transition to a THROTTLED state.
-  int new_renderers_until_throttled_;
-  // When in a NORMAL/THROTTLED state and the potential number of new renderers
-  // drops below this level, the coordinator will transition to a SUSPENDED
-  // state.
-  int new_renderers_until_suspended_;
-  // When in a THROTTLED/SUSPENDED state and the potential number of new
-  // renderers rises above this level, the coordinator will transition to a
-  // NORMAL state.
-  int new_renderers_back_to_normal_;
-  // When in a SUSPENDED state and the potential number of new renderers rises
-  // above this level, the coordinator will transition to a SUSPENDED state.
-  int new_renderers_back_to_throttled_;
-  // The memory coordinator stays in the same state at least this duration even
-  // when there are considerable changes in the amount of free memory to prevent
-  // thrashing.
-  base::TimeDelta minimum_transition_period_;
-  // The interval of checking the amount of free memory.
-  base::TimeDelta monitoring_interval_;
-
-  DISALLOW_COPY_AND_ASSIGN(MemoryStateUpdater);
-};
-
-}  // namespace content
-
-#endif  // CONTENT_BROWSER_MEMORY_MEMORY_STATE_UPDATER_H_