Drop the global memory state from memory coordinator

content/browser/memory/memory_condition_observer.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_CONDITION_OBSERVER_H_
+#define CONTENT_BROWSER_MEMORY_MEMORY_CONDITION_OBSERVER_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 {
+
+// MemoryConditionObserver is an internal implementation of MemoryCoordinator
+// which uses a heuristic to determine the current memory condition. The
+// heuristic is:
+// * 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 memory condition (one of NORMAL/WARNING/CRITICAL) by using some
+//   thresholds and hysteresis.
+class CONTENT_EXPORT MemoryConditionObserver {
+ public:
+  // |coordinator| must outlive than this instance.
+  MemoryConditionObserver(
+      MemoryCoordinatorImpl* coordinator,
+      scoped_refptr<base::SingleThreadTaskRunner> task_runner);
+  ~MemoryConditionObserver();
+
+  // Schedules a task to update memory condition. The task will be executed
+  // after |delay| has passed.
+  void ScheduleUpdateCondition(base::TimeDelta delay);
+
+ private:
+  FRIEND_TEST_ALL_PREFIXES(MemoryCoordinatorImplTest, CalculateNextCondition);
+  FRIEND_TEST_ALL_PREFIXES(MemoryCoordinatorImplTest, UpdateCondition);
+  FRIEND_TEST_ALL_PREFIXES(MemoryCoordinatorImplTest, ForceSetMemoryCondition);
+
+  // Calculates next memory condition from the amount of free memory using
+  // a heuristic.
+  MemoryCondition CalculateNextCondition();
+
+  // Periodically called to update the memory condition.
+  void UpdateCondition();
+
+  MemoryCoordinatorImpl* coordinator_;
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+  base::CancelableClosure update_condition_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 condition and the potential number of new renderers drops
+  // below this level, the coordinator will transition to a WARNING condition.
+  int new_renderers_until_warning_;
+  // When in a NORMAL/WARNING state and the potential number of new renderers
+  // drops below this level, the coordinator will transition to a CRITICAL
+  // condition.
+  int new_renderers_until_critical_;
+  // When in a WARNING/CRITICAL condition and the potential number of new
+  // renderers rises above this level, the coordinator will transition to a
+  // NORMAL condition.
+  int new_renderers_back_to_normal_;
+  // When in a CRITICAL condition and the potential number of new renderers
+  // rises above this level, the coordinator will transition to a WARNING
+  // condition.
+  int new_renderers_back_to_warning_;
+  // The interval of checking the amount of free memory.
+  base::TimeDelta monitoring_interval_;
+
+  DISALLOW_COPY_AND_ASSIGN(MemoryConditionObserver);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_MEMORY_MEMORY_CONDITION_OBSERVER_H_