Resume a backgrounded renderer that was purged and suspended

chrome/browser/memory/tab_manager.cc

Index: chrome/browser/memory/tab_manager.cc
diff --git a/chrome/browser/memory/tab_manager.cc b/chrome/browser/memory/tab_manager.cc
index e761e81a7c43a1d31ef1ebd15c33c984e6faa98b..3223e39cd746bf4c21d58a88ae1ba1db23729b43 100644
--- a/chrome/browser/memory/tab_manager.cc
+++ b/chrome/browser/memory/tab_manager.cc
@@ -84,6 +84,16 @@ const int kRecentTabDiscardIntervalSeconds = 60;
 // machine was suspended and correct the timing statistics.
 const int kSuspendThresholdSeconds = kAdjustmentIntervalSeconds * 4;
 
+// The backgrounded renderer is allowed to be suspended for this duration
+// before resume.

[haraken, 2016/10/20 16:52:16]

A suspended renderer is suspended for this duration.

+constexpr base::TimeDelta kMaxTimeRendererAllowedToBeSuspendedBeforeResume =

[haraken, 2016/10/20 16:52:16]

kDurationOfRendererSuspension ?

+    base::TimeDelta::FromSeconds(120);
+
+// When the suspended backgrounded renderer is resumed, the renderer runs
+// for this duration.

[haraken, 2016/10/20 16:52:16]

A resumed renderer is resumed for this duration.

+constexpr base::TimeDelta kSuspendedRendererLengthOfResumption =

[haraken, 2016/10/20 16:52:16]

kDurationOfRendererResumption ?

+    base::TimeDelta::FromSeconds(10);
+
 // The time during which a tab is protected from discarding after it stops being
 // audible.
 const int kAudioProtectionTimeSeconds = 60;
@@ -418,17 +428,24 @@ void TabManager::SetTabAutoDiscardableState(content::WebContents* contents,
   GetWebContentsData(contents)->SetAutoDiscardableState(state);
 }
 
+content::WebContents* TabManager::GetWebContentsByContentsId(
+    int64_t tab_contents_id) {
+  TabStripModel* model;
+  int index = FindTabStripModelById(tab_contents_id, &model);
+  if (index == -1)
+    return nullptr;
+  return model->GetWebContentsAt(index);
+}
+
 bool TabManager::CanSuspendBackgroundedRenderer(int render_process_id) {
   // A renderer can be suspended if it's not playing media.
   auto tab_stats = GetUnsortedTabStats();
   for (auto& tab : tab_stats) {
     if (tab.child_process_host_id != render_process_id)
       continue;
-    TabStripModel* model;
-    int index = FindTabStripModelById(tab.tab_contents_id, &model);
-    if (index == -1)
+    WebContents* web_contents = GetWebContentsByContentsId(tab.tab_contents_id);
+    if (!web_contents)
       return false;
-    WebContents* web_contents = model->GetWebContentsAt(index);
     if (IsMediaTab(web_contents))
       return false;
   }
@@ -687,6 +704,47 @@ void TabManager::UpdateTimerCallback() {
   PurgeAndSuspendBackgroundedTabs();
 }
 
+bool TabManager::ShouldUpdatePurgeAndSuspendState(
+    const base::TimeTicks& current_time,
+    const TabStats& tab,
+    const base::TimeDelta& purge_and_suspend_threshold,
+    PurgeAndSuspendState* next_state) {
+  DCHECK(next_state);
+  content::WebContents* content =
+      GetWebContentsByContentsId(tab.tab_contents_id);
+  if (!content)
+    return false;
+
+  base::TimeTicks last_modified_time =
+      GetWebContentsData(content)->LastPurgeAndSuspendModifiedTime();
+  PurgeAndSuspendState state =
+      GetWebContentsData(content)->GetPurgeAndSuspendState();
+  DCHECK(state == RUNNING || tab.last_active < last_modified_time);

[haraken, 2016/10/20 16:52:16]

Add a comment about what 'tab.last_active < last_modified_time' means.

+
+  auto time_passed = current_time - last_modified_time;
+  switch (state) {
+    case RUNNING:
+      if (time_passed > purge_and_suspend_threshold) {
+        *next_state = SUSPENDED;
+        return true;
+      }
+      break;
+    case RESUMED:
+      if (time_passed > kSuspendedRendererLengthOfResumption) {
+        *next_state = SUSPENDED;
+        return true;
+      }
+      break;
+    case SUSPENDED:
+      if (time_passed > kMaxTimeRendererAllowedToBeSuspendedBeforeResume) {
+        *next_state = RESUMED;
+        return true;
+      }
+      break;
+  }
+  return false;
+}
+
 void TabManager::PurgeAndSuspendBackgroundedTabs() {
   const base::CommandLine& command_line =
       *base::CommandLine::ForCurrentProcess();
@@ -700,21 +758,36 @@ void TabManager::PurgeAndSuspendBackgroundedTabs() {
   }
   if (purge_and_suspend_time <= 0)
     return;
-  auto purge_and_suspend_time_threshold =
-      NowTicks() - base::TimeDelta::FromSeconds(purge_and_suspend_time);
+  base::TimeTicks current_time = NowTicks();
+  base::TimeDelta purge_and_suspend_threshold =
+      base::TimeDelta::FromSeconds(purge_and_suspend_time);
   auto tab_stats = GetUnsortedTabStats();
   for (auto& tab : tab_stats) {
     if (!tab.render_process_host->IsProcessBackgrounded())
       continue;
+    if (!CanSuspendBackgroundedRenderer(tab.child_process_host_id))
+      continue;
+
     // TODO(hajimehoshi): Now calling PurgeAndSuspend is implemented without
     // timers for simplicity, so PurgeAndSuspend is called even after the
     // renderer is purged and suspended once. This should be replaced with
     // timers if we want necessary and sufficient signals.
-    if (tab.last_active > purge_and_suspend_time_threshold)
+    PurgeAndSuspendState state = RUNNING;
+    if (!ShouldUpdatePurgeAndSuspendState(current_time, tab,

[haraken, 2016/10/20 16:52:16]

How about just making this method return the next state? Then we can compare
next_state with current_state.

+                                          purge_and_suspend_threshold, &state))
       continue;
-    if (!CanSuspendBackgroundedRenderer(tab.child_process_host_id))
-      continue;
-    tab.render_process_host->PurgeAndSuspend();
+    WebContents* content = GetWebContentsByContentsId(tab.tab_contents_id);
+    GetWebContentsData(content)->SetPurgeAndSuspendState(state);
+    switch (state) {
+      case SUSPENDED:
+        tab.render_process_host->PurgeAndSuspend();
+        break;
+      case RESUMED:
+        tab.render_process_host->Resume();
+        break;
+      case RUNNING:
+        NOTREACHED();
+    }
   }
 }
 
@@ -815,6 +888,7 @@ void TabManager::ActiveTabChanged(content::WebContents* old_contents,
                                   int index,
                                   int reason) {
   GetWebContentsData(new_contents)->SetDiscardState(false);
+  GetWebContentsData(new_contents)->SetPurgeAndSuspendState(RUNNING);
   // If |old_contents| is set, that tab has switched from being active to
   // inactive, so record the time of that transition.
   if (old_contents)