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..5e3ec556df6f58b9724e0006762c174b4d9be229 100644
--- a/chrome/browser/memory/tab_manager.cc
+++ b/chrome/browser/memory/tab_manager.cc
@@ -84,6 +84,14 @@ 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
+// suspended, resume the renderer to avoid breaking web.
+const int kResumeSuspendedRendererMinutes = 2;
+
+// After resuming and running a backgrounded renderer for this period,
+// the renderer is purged and suspended again.
+const int kSuspendResumedRendererMinutes = 1;

[haraken, 2016/10/06 08:21:20]

As discussed offline, 1 min => 10 sec?

[tasak, 2016/10/06 08:42:36]

Done.

[dcheng, 2016/10/06 09:55:08]

Nit: this can just be a constexpr base::TimeDelta. Then it can just be used
directly below without having to construct a TimeDelta. The name can be shorter
too because it doesn't need to include the units anymore =)

[tasak, 2016/10/06 10:10:05]

I see.
Done.
Thank you.

[Avi (use Gerrit), 2016/10/18 06:15:36]

dcheng: Are you sure that making a constexpr TimeDelta here doesn't create a
static initializer?

+
 // The time during which a tab is protected from discarding after it stops being
 // audible.
 const int kAudioProtectionTimeSeconds = 60;
@@ -683,8 +691,9 @@ 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 +704,26 @@ 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) >
+          base::TimeDelta::FromMinutes(kSuspendResumedRendererMinutes)))) {
+      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 > base::TimeDelta::FromMinutes(kResumeSuspendedRendererMinutes))
+        tab.render_process_host->Resume();
+    }
   }
 }