Remove timer queue.

SignalServiceKit/src/Util/OWSOperation.m

@@ -18,8 +18,9 @@ NSString *const OWSOperationKeyIsFinished = @"isFinished";
 @property (nullable) NSError *failingError;
 @property (atomic) OWSOperationState operationState;
 @property (nonatomic) OWSBackgroundTask *backgroundTask;
+
+// This property should only be accessed on the main queue.
 @property (nonatomic) NSTimer *_Nullable retryTimer;
-@property (nonatomic, readonly) dispatch_queue_t retryTimerSerialQueue;
 
 @end
 
@@ -34,7 +35,6 @@ NSString *const OWSOperationKeyIsFinished = @"isFinished";
 
     _operationState = OWSOperationStateNew;
     _backgroundTask = [OWSBackgroundTask backgroundTaskWithLabel:self.logTag];
-    _retryTimerSerialQueue = dispatch_queue_create("SignalServiceKit.OWSOperation.retryTimer", DISPATCH_QUEUE_SERIAL);
 
     // Operations are not retryable by default.
     _remainingRetries = 0;
@@ -131,16 +131,15 @@ NSString *const OWSOperationKeyIsFinished = @"isFinished";
 
 - (void)runAnyQueuedRetry
 {
-    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
-        __block NSTimer *_Nullable retryTimer;
-        dispatch_sync(self.retryTimerSerialQueue, ^{
-            retryTimer = self.retryTimer;
+    dispatch_async(dispatch_get_main_queue(), ^{
+        NSTimer *_Nullable retryTimer = self.retryTimer;
         self.retryTimer = nil;
         [retryTimer invalidate];
-        });
 
         if (retryTimer != nil) {
+            dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
                 [self run];
+            });
         } else {
             OWSLogVerbose(@"not re-running since operation is already running.");
         }
@@ -193,9 +192,9 @@ NSString *const OWSOperationKeyIsFinished = @"isFinished";
     self.remainingRetries--;
 
     dispatch_async(dispatch_get_main_queue(), ^{
-        dispatch_sync(self.retryTimerSerialQueue, ^{
         OWSAssertDebug(self.retryTimer == nil);
         [self.retryTimer invalidate];
+
         // The `scheduledTimerWith*` methods add the timer to the current thread's RunLoop.
         // Since Operations typically run on a background thread, that would mean the background
         // thread's RunLoop. However, the OS can spin down background threads if there's no work
@@ -209,7 +208,6 @@ NSString *const OWSOperationKeyIsFinished = @"isFinished";
                                                              userInfo:nil
                                                               repeats:NO];
     });
-    });
 }
 
 // Override in subclass if you want something more sophisticated, e.g. exponential backoff