From 0a3b124a51c29318859acf825a96b5ca87e4ba33 Mon Sep 17 00:00:00 2001
From: "Hedden, Kyle Matthew" <kyle.hedden@verizonwireless.com>
Date: Fri, 25 Jan 2019 13:22:32 -0500
Subject: [PATCH] Add safe queue sync.

---
 .../MVMCore/Utility/Helpers/MVMCoreDispatchUtility.h   |  3 +++
 .../MVMCore/Utility/Helpers/MVMCoreDispatchUtility.m   | 10 ++++++++++
 2 files changed, 13 insertions(+)

diff --git a/MVMCore/MVMCore/Utility/Helpers/MVMCoreDispatchUtility.h b/MVMCore/MVMCore/Utility/Helpers/MVMCoreDispatchUtility.h
index 3cdffb3..982ed5d 100644
--- a/MVMCore/MVMCore/Utility/Helpers/MVMCoreDispatchUtility.h
+++ b/MVMCore/MVMCore/Utility/Helpers/MVMCoreDispatchUtility.h
@@ -18,4 +18,7 @@
 + (void)performBlockInBackground:(nonnull void (^)(void))block;
 + (void)performSyncBlockInBackground:(nonnull void (^)(void))block;
 
+/// Ensures the block is peformed on the same *labeled* dispatch queue. The queue *must* be previously initialized with a unique label.
++ (void)performSyncBlock:(nonnull void (^)(void))block onQueue:(dispatch_queue_t)queue;
+
 @end
diff --git a/MVMCore/MVMCore/Utility/Helpers/MVMCoreDispatchUtility.m b/MVMCore/MVMCore/Utility/Helpers/MVMCoreDispatchUtility.m
index 8ff96fb..9791ace 100644
--- a/MVMCore/MVMCore/Utility/Helpers/MVMCoreDispatchUtility.m
+++ b/MVMCore/MVMCore/Utility/Helpers/MVMCoreDispatchUtility.m
@@ -42,4 +42,14 @@
     }
 }
 
++ (void)performSyncBlock:(nonnull void (^)(void))block onQueue:(dispatch_queue_t)queue {
+    assert(dispatch_queue_get_label(queue) != NULL); // The queue being queried MUST have a label.
+    const char *currQueueLabel = dispatch_queue_get_label(DISPATCH_CURRENT_QUEUE_LABEL);
+    if (!currQueueLabel || strcmp(dispatch_queue_get_label(queue), currQueueLabel) != 0) {
+        dispatch_sync(queue, block);
+    } else {
+        block();
+    }
+}
+
 @end