Bug 1198459 - Add support for disabling e10s if a11y was run in the previous session, or run in a session over the previous week. r=felipe

toolkit/xre/nsAppRunner.cpp

@@ -49,6 +49,7 @@
 #include "prprf.h"
 #include "prproces.h"
 #include "prenv.h"
+#include "prtime.h"
 
 #include "nsIAppShellService.h"
 #include "nsIAppStartup.h"
@@ -4594,6 +4595,17 @@ enum {
   kE10sDisabledForMacGfx = 5,
 };
 
+const char* kAccessibilityLastRunDatePref = "accessibility.lastLoadDate";
+const char* kAccessibilityLoadedLastSessionPref = "accessibility.loadedInLastSession";
+const char* kForceEnableE10sPref = "browser.tabs.remote.force-enable";
+
+static inline uint32_t
+PRTimeToSeconds(PRTime t_usec)
+{
+  PRTime usec_per_sec = PR_USEC_PER_SEC;
+  return uint32_t(t_usec /= usec_per_sec);
+}
+
 bool
 mozilla::BrowserTabsRemoteAutostart()
 {
@@ -4601,6 +4613,37 @@ mozilla::BrowserTabsRemoteAutostart()
     return gBrowserTabsRemoteAutostart;
   }
   gBrowserTabsRemoteAutostartInitialized = true;
+
+  bool disabledForA11y = false;
+#ifdef XP_WIN
+  /**
+   * Avoids enabling e10s if accessibility has recently loaded. Performs the
+   * following checks:
+   * 1) Checks a pref indicating if a11y loaded in the last session. This pref
+   * is set in nsBrowserGlue.js. If a11y was loaded in the last session we
+   * do not enable e10s in this session.
+   * 2) Accessibility stores a last run date (PR_IntervalNow) when it is
+   * initialized (see nsBaseWidget.cpp). We check if this pref exists and
+   * compare it to now. If a11y hasn't run in an extended period of time or
+   * if the date pref does not exist we load e10s.
+   */
+  disabledForA11y = Preferences::GetBool(kAccessibilityLoadedLastSessionPref, false);
+  if (!disabledForA11y  &&
+      Preferences::HasUserValue(kAccessibilityLastRunDatePref)) {
+    #define ONE_WEEK_IN_SECONDS (60*60*24*7)
+    uint32_t a11yRunDate = Preferences::GetInt(kAccessibilityLastRunDatePref, 0);
+    MOZ_ASSERT(0 != a11yRunDate);
+    // If a11y hasn't run for a period of time, clear the pref and load e10s
+    uint32_t now = PRTimeToSeconds(PR_Now());
+    uint32_t difference = now - a11yRunDate;
+    if (difference > ONE_WEEK_IN_SECONDS || !a11yRunDate) {
+      Preferences::ClearUser(kAccessibilityLastRunDatePref);
+    } else {
+      disabledForA11y = true;
+    }
+  }
+#endif
+
   bool optInPref = Preferences::GetBool("browser.tabs.remote.autostart", false);
   bool trialPref = Preferences::GetBool("browser.tabs.remote.autostart.2", false);
   bool prefEnabled = optInPref || trialPref;
@@ -4623,15 +4666,13 @@ mozilla::BrowserTabsRemoteAutostart()
                      gfxPrefs::GetSingleton().LayersOffMainThreadCompositionTestingEnabled();
 #endif
 
-  // Check for some conditions that might disable e10s.
-  bool disabledForA11y = Preferences::GetBool("browser.tabs.remote.disabled-for-a11y", false);
   // Disable for VR
   bool disabledForVR = Preferences::GetBool("dom.vr.enabled", false);
 
   if (e10sAllowed && prefEnabled) {
     if (disabledForA11y) {
       status = kE10sDisabledForAccessibility;
-      LogE10sBlockedReason("An accessibility tool is or was active. See bug 1115956.");
+      LogE10sBlockedReason("An accessibility tool is or was active. See bug 1198459.");
     } else if (disabledForVR) {
       LogE10sBlockedReason("Experimental VR interfaces are enabled");
     } else {
@@ -4678,6 +4719,11 @@ mozilla::BrowserTabsRemoteAutostart()
   }
 #endif // defined(XP_MACOSX)
 
+  // Uber override pref for manual testing purposes
+  if (Preferences::GetBool(kForceEnableE10sPref, false)) {
+    gBrowserTabsRemoteAutostart = true;
+  }
+
   mozilla::Telemetry::Accumulate(mozilla::Telemetry::E10S_AUTOSTART, gBrowserTabsRemoteAutostart);
   mozilla::Telemetry::Accumulate(mozilla::Telemetry::E10S_AUTOSTART_STATUS, status);
   if (Preferences::GetBool("browser.enabledE10SFromPrompt", false)) {

widget/nsBaseWidget.cpp

@@ -1768,6 +1768,16 @@ nsBaseWidget::GetTextEventDispatcher()
 
 #ifdef ACCESSIBILITY
 
+// defined in nsAppRunner.cpp
+extern const char* kAccessibilityLastRunDatePref;
+
+static inline uint32_t
+PRTimeToSeconds(PRTime t_usec)
+{
+  PRTime usec_per_sec = PR_USEC_PER_SEC;
+  return uint32_t(t_usec /= usec_per_sec);
+}
+
 a11y::Accessible*
 nsBaseWidget::GetRootAccessible()
 {
@@ -1786,6 +1796,8 @@ nsBaseWidget::GetRootAccessible()
   nsCOMPtr<nsIAccessibilityService> accService =
     services::GetAccessibilityService();
   if (accService) {
+    uint32_t now = PRTimeToSeconds(PR_Now());
+    Preferences::SetInt(kAccessibilityLastRunDatePref, now);
     return accService->GetRootDocumentAccessible(presShell, nsContentUtils::IsSafeToRunScript());
   }