Resume a backgrounded renderer that was purged and suspended

chrome/browser/memory/tab_manager.cc

 // 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.
 
 #include "chrome/browser/memory/tab_manager.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <set>
@@ skipping 66 matching lines @@
 // For each period of this length record a statistic to indicate whether or not
 // the user experienced a low memory event. If this interval is changed,
 // Tabs.Discard.DiscardInLastMinute must be replaced with a new statistic.
 const int kRecentTabDiscardIntervalSeconds = 60;
 #endif
 
 // If there has been no priority adjustment in this interval, assume the
 // 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.
+constexpr base::TimeDelta kMaxTimeRendererAllowedToBeSuspendedBeforeResume =
+    base::TimeDelta::FromSeconds(120);
+
+// When the suspended backgrounded renderer is resumed, the renderer runs
+// for this duration.
+constexpr base::TimeDelta kSuspendedRendererLengthOfResumption =
+    base::TimeDelta::FromSeconds(10);
+
 // The time during which a tab is protected from discarding after it stops being
 // audible.
 const int kAudioProtectionTimeSeconds = 60;
 
 int FindTabStripModelById(int64_t target_web_contents_id,
                           TabStripModel** model) {
   DCHECK(model);
   for (auto* browser : *BrowserList::GetInstance()) {
     TabStripModel* local_model = browser->tab_strip_model();
     for (int idx = 0; idx < local_model->count(); idx++) {
@@ skipping 314 matching lines @@
 
 bool TabManager::IsTabAutoDiscardable(content::WebContents* contents) const {
   return GetWebContentsData(contents)->IsAutoDiscardable();
 }
 
 void TabManager::SetTabAutoDiscardableState(content::WebContents* contents,
                                             bool state) {
   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;
   }
   return true;
 }
 
 // static
 bool TabManager::CompareTabStats(const TabStats& first,
                                  const TabStats& second) {
   // Being currently selected is most important to protect.
@@ skipping 238 matching lines @@
 
 #if defined(OS_CHROMEOS)
   TabStatsList stats_list = GetTabStats();
   // This starts the CrOS specific OOM adjustments in /proc/<pid>/oom_score_adj.
   delegate_->AdjustOomPriorities(stats_list);
 #endif
 
   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();
+  // If the tab was foregrounded, should ignore the returned state.
+  if (tab.last_active > last_modified_time)

[haraken, 2016/10/19 10:40:30]

Instead of adding this if check, would it be possible to update
WebContentsData::purge_and_suspend_state_ to RUNNING when the tab gets
foregrounded? Then you don't need to add the if check.

I want to make sure that the following invariant holds:

- WebContentsData::purge_and_suspend_state_ == SUSPENDED iff the tab is
suspended
- WebContentsData::purge_and_suspend_state_ == RESUMED iff the tab is resumed
- WebContentsData::purge_and_suspend_state_ == RUNNING otherwise

[tasak, 2016/10/20 11:28:46]

I think, it is very difficult to capture such transitions, i.e.
foregrounded/backgrounded here.
So if we move the state from here to WebContents, it is possible.
But I don't want to make the state public, because the state will be removed (or
moved) when MemoryCoordinator is landed.

[tasak, 2016/10/20 11:47:36]

I found that it is possible to implement  TabManager::ActiveTabChanged.

[tasak, 2016/10/20 12:35:12]

Done.

+    state = BACKGROUNDED;
+
+  auto time_passed = current_time - last_modified_time;
+  switch (state) {
+    case BACKGROUNDED:
+      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();
   if (!command_line.HasSwitch(switches::kPurgeAndSuspendTime))
     return;
   int purge_and_suspend_time = 0;
   if (!base::StringToInt(
           command_line.GetSwitchValueASCII(switches::kPurgeAndSuspendTime),
           &purge_and_suspend_time)) {
     return;
   }
   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 = BACKGROUNDED;
+    if (!ShouldUpdatePurgeAndSuspendState(current_time, tab,
+                                          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 BACKGROUNDED:
+        NOTREACHED();
+    }
   }
 }
 
 WebContents* TabManager::DiscardWebContentsAt(int index, TabStripModel* model) {
   // Can't discard active index.
   if (model->active_index() == index)
     return nullptr;
 
   WebContents* old_contents = model->GetWebContentsAt(index);
 
@@ skipping 231 matching lines @@
   // platform.
   std::string allow_multiple_discards = variations::GetVariationParamValue(
       features::kAutomaticTabDiscarding.name, "AllowMultipleDiscards");
   return (allow_multiple_discards != "true");
 #else
   return false;
 #endif
 }
 
 }  // namespace memory