Resume a backgrounded renderer that was purged and suspended

chrome/browser/memory/tab_manager.h

 // Copyright (c) 2012 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 CHROME_BROWSER_MEMORY_TAB_MANAGER_H_
 #define CHROME_BROWSER_MEMORY_TAB_MANAGER_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 156 matching lines @@
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest, DiscardWebContentsAt);
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest, InvalidOrEmptyURL);
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest, IsInternalPage);
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest, OomPressureListener);
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest, ProtectPDFPages);
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest, ProtectRecentlyUsedTabs);
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest, ProtectVideoTabs);
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest, ReloadDiscardedTabContextMenu);
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest, TabManagerBasics);
 
-  // This is needed so WebContentsData can call OnDiscardedStateChange.
-  friend class WebContensData;
+  // This is needed so WebContentsData can call OnDiscardedStateChange, and
+  // can use PurgeAndSuspendState.
+  friend class WebContentsData;
 
   // Called by WebContentsData whenever the discard state of a WebContents
   // changes, so that observers can be informed.
   void OnDiscardedStateChange(content::WebContents* contents,
                               bool is_discarded);
 
   // Called by WebContentsData whenever the auto-discardable state of a
   // WebContents changes, so that observers can be informed.
   void OnAutoDiscardableStateChange(content::WebContents* contents,
                                     bool is_auto_discardable);
@@ skipping 51 matching lines @@
   // If |active_model| is true, consider its first tab as being active.
   void AddTabStats(const TabStripModel* model,
                    bool is_app,
                    bool active_model,
                    TabStatsList* stats_list);
 
   // Callback for when |update_timer_| fires. Takes care of executing the tasks
   // that need to be run periodically (see comment in implementation).
   void UpdateTimerCallback();
 
+  // Returns WebContents whose contents id matches the given tab-contents-id.
+  content::WebContents* GetWebContentsByContentsId(int64_t tab_contents_id);
+
+  // Initially PurgeAndSuspendState is RUNNING.
+  // RUNNING => SUSPENDED
+  // - Some tab has been backgrounded for more than purge-and-suspend-time
+  //   seconds.
+  // SUSPENDED => RESUMED
+  // - A suspended tab is still suspended (i.e. last active time < last
+  //   purge-and-suspend modified time), and
+  // - kMaxTimeRendererAllowedToBeSuspendedBeforeResume time passes since
+  //   since the tab was suspended.
+  // RESUMED => SUSPENDED
+  // - A resumed tab is still backgrounded (i.e. last active time < last
+  //   purge-and-suspend modified time), and
+  // - kSuspendedRendererLengthOfResumption time passes since the tab was
+  //   resumed.
+  // SUSPENDED, RESUMED => SUSPENDED
+  // - Since it is difficult to capture OnProcessBackgrounded or
+  //   OnProcessForegrounded in TabManager, compare last active time with
+  //   last purge-and-suspend modified time.
+  // - if last active time > last purge-and-suspend modified time,
+  //   the tab was foregrounded and is not suspended.
+  //   So we treat the state as RUNNING.
+  enum PurgeAndSuspendState {
+    RUNNING,
+    RESUMED,
+    SUSPENDED,
+  };
+  // Determines whether to update purge-and-suspend state and returns the
+  // next state.
+  bool ShouldUpdatePurgeAndSuspendState(
+      const base::TimeTicks& current_time,
+      const TabStats& tab,
+      const base::TimeDelta& purge_and_suspend_threshold,
+      PurgeAndSuspendState* next_state);
+
   // Purges and suspends renderers in backgrounded tabs.
   void PurgeAndSuspendBackgroundedTabs();
 
   // Does the actual discard by destroying the WebContents in |model| at |index|
   // and replacing it by an empty one. Returns the new WebContents or NULL if
   // the operation fails (return value used only in testing).
   content::WebContents* DiscardWebContentsAt(int index, TabStripModel* model);
 
   // Called by the memory pressure listener when the memory pressure rises.
   void OnMemoryPressure(
@@ skipping 122 matching lines @@
 
   // Weak pointer factory used for posting delayed tasks to task_runner_.
   base::WeakPtrFactory<TabManager> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(TabManager);
 };
 
 }  // namespace memory
 
 #endif  // CHROME_BROWSER_MEMORY_TAB_MANAGER_H_