Bug 1384336 - Stop using OS-level event loop in content process (r=ms…

…tange)

MozReview-Commit-ID: 1ouSlgGchWl

dom/ipc/ContentChild.cpp

@@ -1452,6 +1452,11 @@ GetDirectoryPath(const char *aPath) {
 }
 #endif // DEBUG
 
+extern "C" {
+void CGSSetDenyWindowServerConnections(bool);
+void CGSShutdownServerConnections();
+};
+
 static bool
 StartMacOSContentSandbox()
 {
@@ -1460,6 +1465,15 @@ StartMacOSContentSandbox()
     return false;
   }
 
+  if (!XRE_UseNativeEventProcessing()) {
+    // If we've opened a connection to the window server, shut it down now. Forbid
+    // future connections as well. We do this for sandboxing, but it also ensures
+    // that the Activity Monitor will not label the content process as "Not
+    // responding" because it's not running a native event loop. See bug 1384336.
+    CGSSetDenyWindowServerConnections(true);
+    CGSShutdownServerConnections();
+  }
+
   nsAutoCString appPath, appBinaryPath, appDir;
   if (!GetAppPaths(appPath, appBinaryPath, appDir)) {
     MOZ_CRASH("Error resolving child process path");

dom/ipc/ContentPrefs.cpp

@@ -52,6 +52,7 @@ const char* mozilla::dom::ContentPrefs::gInitPrefs[] = {
   "dom.forms.autocomplete.formautofill",
   "dom.ipc.processPriorityManager.backgroundGracePeriodMS",
   "dom.ipc.processPriorityManager.backgroundPerceivableGracePeriodMS",
+  "dom.ipc.useNativeEventProcessing.content",
   "dom.max_chrome_script_run_time",
   "dom.max_script_run_time",
   "dom.mozBrowserFramesEnabled",

modules/libpref/init/all.js

@@ -3239,6 +3239,9 @@ pref("dom.ipc.processCount.file", 1);
 // WebExtensions only support a single extension process.
 pref("dom.ipc.processCount.extension", 1);
 
+// Don't use a native event loop in the content process.
+pref("dom.ipc.useNativeEventProcessing.content", false);
+
 // Disable support for SVG
 pref("svg.disabled", false);
 

toolkit/xre/nsAppRunner.cpp

@@ -5012,6 +5012,24 @@ XRE_IsContentProcess()
   return XRE_GetProcessType() == GeckoProcessType_Content;
 }
 
+bool
+XRE_UseNativeEventProcessing()
+{
+  if (XRE_IsContentProcess()) {
+    static bool sInited = false;
+    static bool sUseNativeEventProcessing = false;
+    if (!sInited) {
+      Preferences::AddBoolVarCache(&sUseNativeEventProcessing,
+                                   "dom.ipc.useNativeEventProcessing.content");
+      sInited = true;
+    }
+
+    return sUseNativeEventProcessing;
+  }
+
+  return true;
+}
+
 // If you add anything to this enum, please update about:support to reflect it
 enum {
   kE10sEnabledByUser = 0,

toolkit/xre/nsEmbedFunctions.cpp

@@ -839,7 +839,7 @@ XRE_RunAppShell()
     nsCOMPtr<nsIAppShell> appShell(do_GetService(kAppShellCID));
     NS_ENSURE_TRUE(appShell, NS_ERROR_FAILURE);
 #if defined(XP_MACOSX)
-    {
+    if (XRE_UseNativeEventProcessing()) {
       // In content processes that want XPCOM (and hence want
       // AppShell), we usually run our hybrid event loop through
       // MessagePump::Run(), by way of nsBaseAppShell::Run().  The

widget/cocoa/nsAppShell.mm

@@ -682,13 +682,19 @@ - (void)beginMenuTracking:(NSNotification*)aNotification;
     AddScreenWakeLockListener();
   }
 
-  NS_OBJC_TRY_ABORT([NSApp run]);
+  // We use the native Gecko event loop in content processes.
+  nsresult rv = NS_OK;
+  if (XRE_UseNativeEventProcessing()) {
+    NS_OBJC_TRY_ABORT([NSApp run]);
+  } else {
+    rv = nsBaseAppShell::Run();
+  }
 
   if (XRE_IsParentProcess()) {
     RemoveScreenWakeLockListener();
   }
 
-  return NS_OK;
+  return rv;
 }
 
 NS_IMETHODIMP

widget/nsBaseAppShell.cpp

@@ -46,11 +46,13 @@ nsBaseAppShell::Init()
 {
   // Configure ourselves as an observer for the current thread:
 
-  nsCOMPtr<nsIThreadInternal> threadInt =
+  if (XRE_UseNativeEventProcessing()) {
+    nsCOMPtr<nsIThreadInternal> threadInt =
       do_QueryInterface(NS_GetCurrentThread());
-  NS_ENSURE_STATE(threadInt);
+    NS_ENSURE_STATE(threadInt);
 
-  threadInt->SetObserver(this);
+    threadInt->SetObserver(this);
+  }
 
   nsCOMPtr<nsIObserverService> obsSvc =
     mozilla::services::GetObserverService();

xpcom/build/nsXULAppAPI.h

@@ -462,6 +462,13 @@ XRE_API(bool,
 XRE_API(bool,
         XRE_IsGPUProcess, ())
 
+/**
+ * Returns true if the appshell should run its own native event loop. Returns
+ * false if we should rely solely on the Gecko event loop.
+ */
+XRE_API(bool,
+        XRE_UseNativeEventProcessing, ())
+
 typedef void (*MainFunction)(void* aData);
 
 XRE_API(nsresult,