Bug 1364849 - Recycle short lived content processes. r=mrbkap

To prevent addons or other code to rapidly create and destroy content processes
under various conditions, we let the preallocated process manager to reuse short
lived content processes.

dom/ipc/ContentParent.cpp

@@ -862,12 +862,17 @@ ContentParent::GetNewOrUsedBrowserProcess(const nsAString& aRemoteType,
     }
 
     // Try to take the preallocated process only for the default process type.
+    // The preallocated process manager might not had the chance yet to release the process
+    // after a very recent ShutDownProcess, let's make sure we don't try to reuse a process
+    // that is being shut down.
     RefPtr<ContentParent> p;
     if (aRemoteType.EqualsLiteral(DEFAULT_REMOTE_TYPE) &&
-        (p = PreallocatedProcessManager::Take())) {
+        (p = PreallocatedProcessManager::Take()) &&
+        !p->mShutdownPending) {
       // For pre-allocated process we have not set the opener yet.
       p->mOpener = aOpener;
       contentParents.AppendElement(p);
+      p->mActivateTS = TimeStamp::Now();
       return p.forget();
     }
   }
@@ -882,6 +887,7 @@ ContentParent::GetNewOrUsedBrowserProcess(const nsAString& aRemoteType,
   p->Init();
 
   contentParents.AppendElement(p);
+  p->mActivateTS = TimeStamp::Now();
   return p.forget();
 }
 
@@ -1522,7 +1528,7 @@ ContentParent::ShutDownMessageManager()
 }
 
 void
-ContentParent::MarkAsTroubled()
+ContentParent::RemoveFromList()
 {
   if (IsForJSPlugin()) {
     if (sJSPluginContentParents) {
@@ -1554,6 +1560,12 @@ ContentParent::MarkAsTroubled()
       sPrivateContent = nullptr;
     }
   }
+}
+
+void
+ContentParent::MarkAsTroubled()
+{
+  RemoveFromList();
   mIsAvailable = false;
 }
 
@@ -1854,6 +1866,26 @@ ContentParent::ActorDestroy(ActorDestroyReason why)
 #endif
 }
 
+bool
+ContentParent::TryToRecycle()
+{
+  // This life time check should be replaced by a memory health check (memory usage + fragmentation).
+  const double kMaxLifeSpan = 5;
+  if (mShutdownPending ||
+      mCalledKillHard ||
+      !IsAvailable() ||
+      !mRemoteType.EqualsLiteral(DEFAULT_REMOTE_TYPE) ||
+      (TimeStamp::Now() - mActivateTS).ToSeconds() > kMaxLifeSpan ||
+      !PreallocatedProcessManager::Provide(this)) {
+    return false;
+  }
+
+  // The PreallocatedProcessManager took over the ownership let's not keep a reference to it,
+  // until we don't take it back.
+  RemoveFromList();
+  return true;
+}
+
 bool
 ContentParent::ShouldKeepProcessAlive() const
 {
@@ -1916,6 +1948,10 @@ ContentParent::NotifyTabDestroying(const TabId& aTabId,
       return;
     }
 
+    if (cp->TryToRecycle()) {
+      return;
+    }
+
     // We're dying now, so prevent this content process from being
     // recycled during its shutdown procedure.
     cp->MarkAsDead();
@@ -1965,7 +2001,7 @@ ContentParent::NotifyTabDestroyed(const TabId& aTabId,
   ContentProcessManager* cpm = ContentProcessManager::GetSingleton();
   nsTArray<TabId> tabIds = cpm->GetTabParentsByProcessId(this->ChildID());
 
-  if (tabIds.Length() == 1 && !ShouldKeepProcessAlive()) {
+  if (tabIds.Length() == 1 && !ShouldKeepProcessAlive() && !TryToRecycle()) {
     // In the case of normal shutdown, send a shutdown message to child to
     // allow it to perform shutdown tasks.
     MessageLoop::current()->PostTask(NewRunnableMethod
@@ -2103,6 +2139,7 @@ ContentParent::ContentParent(ContentParent* aOpener,
   : nsIContentParent()
   , mSubprocess(nullptr)
   , mLaunchTS(TimeStamp::Now())
+  , mActivateTS(TimeStamp::Now())
   , mOpener(aOpener)
   , mRemoteType(aRemoteType)
   , mChildID(gContentChildID++)

dom/ipc/ContentParent.h

@@ -750,6 +750,17 @@ private:
   // called after the process has been transformed to browser.
   void ForwardKnownInfo();
 
+  /**
+   * We might want to reuse barely used content processes if certain criteria are met.
+   */
+  bool TryToRecycle();
+
+  /**
+   * Removing it from the static array so it won't be returned for new tabs in
+   * GetNewOrUsedBrowserProcess.
+   */
+  void RemoveFromList();
+
   /**
    * Decide whether the process should be kept alive even when it would normally
    * be shut down, for example when all its tabs are closed.
@@ -1182,6 +1193,7 @@ private:
 
   GeckoChildProcessHost* mSubprocess;
   const TimeStamp mLaunchTS; // used to calculate time to start content process
+  TimeStamp mActivateTS;
   ContentParent* mOpener;
 
   nsString mRemoteType;

dom/ipc/PreallocatedProcessManager.cpp

@@ -43,6 +43,7 @@ public:
   void AllocateOnIdle();
   void AllocateNow();
   already_AddRefed<ContentParent> Take();
+  bool Provide(ContentParent* aParent);
 
 private:
   static mozilla::StaticRefPtr<PreallocatedProcessManagerImpl> sSingleton;
@@ -163,9 +164,26 @@ PreallocatedProcessManagerImpl::RereadPrefs()
 already_AddRefed<ContentParent>
 PreallocatedProcessManagerImpl::Take()
 {
+  if (!mEnabled || mShutdown) {
+    return nullptr;
+  }
+
   return mPreallocatedProcess.forget();
 }
 
+bool
+PreallocatedProcessManagerImpl::Provide(ContentParent* aParent)
+{
+  if (mEnabled && !mShutdown && !mPreallocatedProcess) {
+    mPreallocatedProcess = aParent;
+  }
+
+  // We might get a call from both NotifyTabDestroying and NotifyTabDestroyed with the same
+  // ContentParent. Returning true here for both calls is important to avoid the cached process
+  // to be destroyed.
+  return aParent == mPreallocatedProcess;
+}
+
 void
 PreallocatedProcessManagerImpl::Enable()
 {
@@ -282,4 +300,10 @@ PreallocatedProcessManager::Take()
   return GetPPMImpl()->Take();
 }
 
+/* static */ bool
+PreallocatedProcessManager::Provide(ContentParent* aParent)
+{
+  return GetPPMImpl()->Provide(aParent);
+}
+
 } // namespace mozilla

dom/ipc/PreallocatedProcessManager.h

@@ -72,6 +72,8 @@ public:
    */
   static already_AddRefed<ContentParent> Take();
 
+  static bool Provide(ContentParent* aParent);
+
 private:
   PreallocatedProcessManager();
   DISALLOW_EVIL_CONSTRUCTORS(PreallocatedProcessManager);