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 582b2e667099f6fa0085f6721c4b9c69a37709c8..7160d4bc180954ef11ad8ff367c86be79c48655a 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;
 
+// If a backgrounded renderer is kept backgrounded during this time after

[Sami, 2016/10/06 13:10:09]

s/during/for/
/after suspended/after being suspended/

?

[tasak, 2016/10/07 05:31:26]

Done.

+// suspended, resume the renderer to avoid breaking web.
+constexpr base::TimeDelta kSuspendResumedRendererTime =
+    base::TimeDelta::FromSeconds(120);
+
+// After resuming and running a backgrounded renderer for this period,
+// the renderer is purged and suspended again.
+constexpr base::TimeDelta kResumeSuspendedRendererTime =
+    base::TimeDelta::FromSeconds(10);
+
 // The time during which a tab is protected from discarding after it stops being
 // audible.
 const int kAudioProtectionTimeSeconds = 60;
@@ -683,8 +693,9 @@ void TabManager::PurgeAndSuspendBackgroundedTabs() {
   }
   if (purge_and_suspend_time <= 0)
     return;
+  base::TimeTicks current_time = NowTicks();
   auto purge_and_suspend_time_threshold =
-      NowTicks() - base::TimeDelta::FromSeconds(purge_and_suspend_time);
+      current_time - base::TimeDelta::FromSeconds(purge_and_suspend_time);
   auto tab_stats = GetUnsortedTabStats();
   for (auto& tab : tab_stats) {
     if (!tab.render_process_host->IsProcessBackgrounded())
@@ -695,7 +706,25 @@ void TabManager::PurgeAndSuspendBackgroundedTabs() {
     // timers if we want necessary and sufficient signals.
     if (tab.last_active > purge_and_suspend_time_threshold)
       continue;
-    tab.render_process_host->PurgeAndSuspend();
+
+    auto last_purged_and_suspended_time =
+        tab.render_process_host->GetLastPurgedAndSuspendedTime();
+    auto last_resumed_time =
+        tab.render_process_host->GetLastResumedInBackgroundTime();
+
+    if (last_purged_and_suspended_time < tab.last_active ||
+        (last_resumed_time > last_purged_and_suspended_time &&
+         last_purged_and_suspended_time > tab.last_active &&
+         ((current_time - last_resumed_time) > kSuspendResumedRendererTime))) {
+      tab.render_process_host->PurgeAndSuspend();
+      if (!task_runner_.get())
+        task_runner_ = base::ThreadTaskRunnerHandle::Get();
+    } else {
+      auto delta = current_time - last_purged_and_suspended_time;
+      if (last_resumed_time < last_purged_and_suspended_time &&
+          delta > kResumeSuspendedRendererTime)
+        tab.render_process_host->Resume();
+    }
   }
 }