Bug 781742: Try to keep a process pre-launched for app content, if the pref says to. r=jlebar

b2g/app/b2g.js

@@ -502,3 +502,9 @@ pref("hal.processPriorityManager.gonk.backgroundOomAdjust", 2);
 pref("hal.processPriorityManager.gonk.masterNice", -1);
 pref("hal.processPriorityManager.gonk.foregroundNice", 0);
 pref("hal.processPriorityManager.gonk.backgroundNice", 10);
+
+// Enable pre-launching content processes for improved startup time
+// (hiding latency).
+pref("dom.ipc.processPrelauch.enabled", true);
+// Wait this long before pre-launching a new subprocess.
+pref("dom.ipc.processPrelauch.delayMs", 1000);

dom/ipc/ContentParent.cpp

@@ -21,10 +21,7 @@
 #include "IndexedDBParent.h"
 #include "IndexedDatabaseManager.h"
 #include "mozIApplication.h"
-#include "mozilla/Preferences.h"
-#include "mozilla/Preferences.h"
-#include "mozilla/Services.h"
-#include "mozilla/Util.h"
+#include "mozilla/ClearOnShutdown.h"
 #include "mozilla/dom/ExternalHelperAppParent.h"
 #include "mozilla/dom/PMemoryReportRequestParent.h"
 #include "mozilla/dom/StorageParent.h"
@@ -34,6 +31,10 @@
 #include "mozilla/ipc/TestShellParent.h"
 #include "mozilla/layers/CompositorParent.h"
 #include "mozilla/net/NeckoParent.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/Services.h"
+#include "mozilla/StaticPtr.h"
+#include "mozilla/Util.h"
 #include "mozilla/unused.h"
 #include "nsAppDirectoryServiceDefs.h"
 #include "nsAppDirectoryServiceDefs.h"
@@ -158,6 +159,93 @@ nsTArray<ContentParent*>* ContentParent::gPrivateContent;
 // The first content child has ID 1, so the chrome process can have ID 0.
 static PRUint64 gContentChildID = 1;
 
+// Try to keep an app process always preallocated, to get
+// initialization off the critical path of app startup.
+static bool sKeepAppProcessPreallocated;
+static StaticRefPtr<ContentParent> sPreallocatedAppProcess;
+static CancelableTask* sPreallocateAppProcessTask;
+// This number is fairly arbitrary ... the intention is to put off
+// launching another app process until the last one has finished
+// loading its content, to reduce CPU/memory/IO contention.
+static int sPreallocateDelayMs;
+// We want the prelaunched process to know that it's for apps, but not
+// actually for any app in particular.  Use a magic manifest URL.
+// Can't be a static constant.
+#define MAGIC_PREALLOCATED_APP_MANIFEST_URL NS_LITERAL_STRING("{{template}}")
+
+/*static*/ void
+ContentParent::PreallocateAppProcess()
+{
+    MOZ_ASSERT(!sPreallocatedAppProcess);
+
+    if (sPreallocateAppProcessTask) {
+        // We were called directly while a delayed task was scheduled.
+        sPreallocateAppProcessTask->Cancel();
+        sPreallocateAppProcessTask = nullptr;
+    }
+
+    sPreallocatedAppProcess =
+        new ContentParent(MAGIC_PREALLOCATED_APP_MANIFEST_URL);
+    sPreallocatedAppProcess->Init();
+}
+
+/*static*/ void
+ContentParent::DelayedPreallocateAppProcess()
+{
+    sPreallocateAppProcessTask = nullptr;
+    if (!sPreallocatedAppProcess) {
+        PreallocateAppProcess();
+    }
+}
+
+/*static*/ void
+ContentParent::ScheduleDelayedPreallocateAppProcess()
+{
+    if (!sKeepAppProcessPreallocated || sPreallocateAppProcessTask) {
+        return;
+    }
+    sPreallocateAppProcessTask =
+        NewRunnableFunction(DelayedPreallocateAppProcess);
+    MessageLoop::current()->PostDelayedTask(
+        FROM_HERE, sPreallocateAppProcessTask, sPreallocateDelayMs);
+}
+
+/*static*/ already_AddRefed<ContentParent>
+ContentParent::MaybeTakePreallocatedAppProcess()
+{
+    nsRefPtr<ContentParent> process = sPreallocatedAppProcess.get();
+    sPreallocatedAppProcess = nullptr;
+    ScheduleDelayedPreallocateAppProcess();
+    return process.forget();
+}
+
+/*static*/ void
+ContentParent::StartUp()
+{
+    if (XRE_GetProcessType() != GeckoProcessType_Default) {
+        return;
+    }
+
+    sKeepAppProcessPreallocated =
+        Preferences::GetBool("dom.ipc.processPrelauch.enabled", false);
+    if (sKeepAppProcessPreallocated) {
+        ClearOnShutdown(&sPreallocatedAppProcess);
+
+        sPreallocateDelayMs = Preferences::GetUint(
+            "dom.ipc.processPrelauch.delayMs", 1000);
+
+        MOZ_ASSERT(!sPreallocateAppProcessTask);
+        ScheduleDelayedPreallocateAppProcess();
+    }
+}
+
+/*static*/ void
+ContentParent::ShutDown()
+{
+    // No-op for now.  We rely on normal process shutdown and
+    // ClearOnShutdown() to clean up our state.
+}
+
 /*static*/ ContentParent*
 ContentParent::GetNewOrUsed()
 {
@@ -225,10 +313,16 @@ ContentParent::CreateBrowser(mozIApplication* aApp, bool aIsBrowserElement)
         return nullptr;
     }
 
-    ContentParent* p = gAppContentParents->Get(manifestURL);
+    nsRefPtr<ContentParent> p = gAppContentParents->Get(manifestURL);
     if (!p) {
-        p = new ContentParent(manifestURL);
-        p->Init();
+        p = MaybeTakePreallocatedAppProcess();
+        if (p) {
+            p->SetManifestFromPreallocated(manifestURL);
+        } else {
+            NS_WARNING("Unable to use pre-allocated app process");
+            p = new ContentParent(manifestURL);
+            p->Init();
+        }
         gAppContentParents->Put(manifestURL, p);
     }
 
@@ -302,7 +396,16 @@ ContentParent::Init()
 }
 
 void
-ContentParent::ShutDown()
+ContentParent::SetManifestFromPreallocated(const nsAString& aAppManifestURL)
+{
+    MOZ_ASSERT(mAppManifestURL == MAGIC_PREALLOCATED_APP_MANIFEST_URL);
+    // Clients should think of mAppManifestURL as const ... we're
+    // bending the rules here just for the preallocation hack.
+    const_cast<nsString&>(mAppManifestURL) = aAppManifestURL;
+}
+
+void
+ContentParent::ShutDownProcess()
 {
     if (mIsAlive) {
         // Close() can only be called once.  It kicks off the
@@ -447,6 +550,10 @@ ContentParent::ActorDestroy(ActorDestroyReason why)
 #endif
     }
 
+    if (sPreallocatedAppProcess == this) {
+        sPreallocatedAppProcess = nullptr;
+    }
+
     mMessageManager->Disconnect();
 
     // clear the child memory reporters
@@ -513,7 +620,7 @@ ContentParent::NotifyTabDestroyed(PBrowserParent* aTab)
     if (IsForApp() && ManagedPBrowserParent().Length() == 1) {
         MessageLoop::current()->PostTask(
             FROM_HERE,
-            NewRunnableMethod(this, &ContentParent::ShutDown));
+            NewRunnableMethod(this, &ContentParent::ShutDownProcess));
     }
 }
 

dom/ipc/ContentParent.h

@@ -58,6 +58,14 @@ private:
     typedef mozilla::dom::ClonedMessageData ClonedMessageData;
 
 public:
+    /**
+     * Start up the content-process machinery.  This might include
+     * scheduling pre-launch tasks.
+     */
+    static void StartUp();
+    /** Shut down the content-process machinery. */
+    static void ShutDown();
+
     static ContentParent* GetNewOrUsed();
 
     /**
@@ -112,6 +120,11 @@ private:
     static nsTArray<ContentParent*>* gNonAppContentParents;
     static nsTArray<ContentParent*>* gPrivateContent;
 
+    static void PreallocateAppProcess();
+    static void DelayedPreallocateAppProcess();
+    static void ScheduleDelayedPreallocateAppProcess();
+    static already_AddRefed<ContentParent> MaybeTakePreallocatedAppProcess();
+
     // Hide the raw constructor methods since we don't want client code
     // using them.
     using PContentParent::SendPBrowserConstructor;
@@ -122,6 +135,10 @@ private:
 
     void Init();
 
+    // Transform a pre-allocated app process into a "real" app
+    // process, for the specified manifest URL.
+    void SetManifestFromPreallocated(const nsAString& aAppManifestURL);
+
     /**
      * Mark this ContentParent as dead for the purposes of Get*().
      * This method is idempotent.
@@ -134,7 +151,7 @@ private:
      * by the Get*() funtions.  However, the shutdown sequence itself
      * may be asynchronous.
      */
-    void ShutDown();
+    void ShutDownProcess();
 
     PCompositorParent* AllocPCompositor(mozilla::ipc::Transport* aTransport,
                                         base::ProcessId aOtherProcess) MOZ_OVERRIDE;

layout/build/nsLayoutStatics.cpp

@@ -2,6 +2,8 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+#include "base/basictypes.h"
+
 #include "nsLayoutStatics.h"
 #include "nscore.h"
 
@@ -94,6 +96,7 @@
 #include "nsHyphenationManager.h"
 #include "nsEditorSpellCheck.h"
 #include "nsWindowMemoryReporter.h"
+#include "mozilla/dom/ContentParent.h"
 #include "mozilla/dom/ipc/ProcessPriorityManager.h"
 
 extern void NS_ShutdownChainItemPool();
@@ -116,6 +119,8 @@ nsLayoutStatics::Initialize()
 
   nsresult rv;
 
+  ContentParent::StartUp();
+
   // Register all of our atoms once
   nsCSSAnonBoxes::AddRefAtoms();
   nsCSSPseudoClasses::AddRefAtoms();
@@ -344,4 +349,6 @@ nsLayoutStatics::Shutdown()
   nsHyphenationManager::Shutdown();
   nsEditorSpellCheck::ShutDown();
   nsDOMMutationObserver::Shutdown();
+
+  ContentParent::ShutDown();
 }