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), ^{
+    dispatch_async(dispatch_get_main_queue(), ^{
-        __block NSTimer *_Nullable retryTimer;
+        NSTimer *_Nullable retryTimer = self.retryTimer;
-        dispatch_sync(self.retryTimerSerialQueue, ^{
+        self.retryTimer = nil;
-            retryTimer = self.retryTimer;
+        [retryTimer invalidate];
-            self.retryTimer = nil;
-            [retryTimer invalidate];
-        });
 
         if (retryTimer != nil) {
-            [self run];
+            dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
+                [self run];
+            });
         } else {
             OWSLogVerbose(@"not re-running since operation is already running.");
         }
@@ -193,22 +192,21 @@ NSString *const OWSOperationKeyIsFinished = @"isFinished";
     self.remainingRetries--;
 
     dispatch_async(dispatch_get_main_queue(), ^{
-        dispatch_sync(self.retryTimerSerialQueue, ^{
+        OWSAssertDebug(self.retryTimer == nil);
-            OWSAssertDebug(self.retryTimer == nil);
+        [self.retryTimer invalidate];
-            [self.retryTimer invalidate];
+
-            // The `scheduledTimerWith*` methods add the timer to the current thread's RunLoop.
+        // 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
+        // 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
+        // thread's RunLoop. However, the OS can spin down background threads if there's no work
-            // being done, so we run the risk of the timer's RunLoop being deallocated before it's
+        // being done, so we run the risk of the timer's RunLoop being deallocated before it's
-            // fired.
+        // fired.
-            //
+        //
-            // To ensure the timer's thread sticks around, we schedule it while on the main RunLoop.
+        // To ensure the timer's thread sticks around, we schedule it while on the main RunLoop.
-            self.retryTimer = [NSTimer weakScheduledTimerWithTimeInterval:self.retryInterval
+        self.retryTimer = [NSTimer weakScheduledTimerWithTimeInterval:self.retryInterval
-                                                                   target:self
+                                                               target:self
-                                                                 selector:@selector(runAnyQueuedRetry)
+                                                             selector:@selector(runAnyQueuedRetry)
-                                                                 userInfo:nil
+                                                             userInfo:nil
-                                                                  repeats:NO];
+                                                              repeats:NO];
-        });
     });
 }