Add a config flag for turning off main queue synchronization.

AppFramework/Config/GREYAppConfiguration.m

@@ -126,6 +126,7 @@ static BOOL IsStandaloneMode(void) {
       kGREYConfigKeyInteractionTimeoutDuration : @(30),
       kGREYConfigKeyCALayerMaxAnimationDuration : @(10),
       kGREYConfigKeySynchronizationEnabled : @YES,
+      kGREYConfigKeyMainQueueTrackingEnabled : @YES,
       kGREYConfigKeyNSTimerMaxTrackableInterval : @(1.5),
       kGREYConfigKeyCALayerModifyAnimations : @YES,
       kGREYConfigKeyDispatchAfterMaxTrackableDelay : @(1.5),

AppFramework/IdlingResources/GREYDispatchQueueIdlingResource.m

@@ -65,7 +65,13 @@ - (BOOL)isIdleNow {
   if (trackerIsIdle && isDead) {
     [[GREYUIThreadExecutor sharedInstance] deregisterIdlingResource:self];
   }
-  return trackerIsIdle;
+  // In apps with unusually high main thread activity, the main thread may never be condidered
+  // idle, or may only rarely become idle.  This is a safety valve to allow this tracker to be
+  // selectively disabled, because otherwise, tests that should take seconds can take minues or
+  // even hours.
+  BOOL mainQueueTrackingEnabled = [GREYConfiguration.sharedConfiguration
+      valueForConfigKey:kGREYConfigKeyMainQueueTrackingEnabled];
+  return trackerIsIdle || !mainQueueTrackingEnabled;
 }
 
 @end

CommonLib/Config/GREYConfigKey.h

@@ -54,6 +54,16 @@ GREY_EXTERN GREYConfigKey const kGREYConfigKeyInteractionTimeoutDuration;
  */
 GREY_EXTERN GREYConfigKey const kGREYConfigKeySynchronizationEnabled;
 
+/**
+ * Configuration that enables or disables EarlGrey's main queue tracking.  When disabled, Earl Grey
+ * will not wait for the main queue to become idle.  All other synchronization remains enabled.
+ *
+ * @remark This can make apps with high levels of main thread activity testable.  If you find
+ * yourself having to enable this, you should actively look for ways to move activity off of the
+ * main thread if at all possible, for both performance and battery life reasons.
+ */
+GREY_EXTERN GREYConfigKey const kGREYConfigKeyMainQueueTrackingEnabled;
+
 /**
  * Configuration that enables synchronization for different app state. By default, EarlGrey will
  * wait for all tracked app state resources to be idle. Set this config value to options with @c

CommonLib/Config/GREYConfigKey.m

@@ -21,6 +21,8 @@
 GREYConfigKey const kGREYConfigKeyInteractionTimeoutDuration =
     @"GREYConfigKeyInteractionTimeoutDuration";
 GREYConfigKey const kGREYConfigKeySynchronizationEnabled = @"GREYConfigKeySynchronizationEnabled";
+GREYConfigKey const kGREYConfigKeyMainQueueTrackingEnabled =
+    @"GREYConfigKeyMainQueueTrackingEnabled";
 GREYConfigKey const kGREYConfigKeyNSTimerMaxTrackableInterval =
     @"GREYConfigKeyNSTimerMaxTrackableInterval";
 GREYConfigKey const kGREYConfigKeyCALayerModifyAnimations = @"GREYConfigKeyCALayerModifyAnimations";