Run deallocBlocks on the FIC dispatch queue so the main thread won't get blocked trying to acquire the FIC lock as an image is deallocated.

Author: Mallory Paine

FastImageCache/FICImageCache.h

@@ -45,6 +45,8 @@ typedef void (^FICImageRequestCompletionBlock)(UIImage *sourceImage);
  */
 + (instancetype)sharedImageCache;
 
++ (dispatch_queue_t)dispatchQueue;
+
 ///---------------------------------
 /// @name Working with Image Formats
 ///---------------------------------

FastImageCache/FICImageCache.m

@@ -53,7 +53,6 @@ - (void)setDelegate:(id<FICImageCacheDelegate>)delegate {
 }
 
 static FICImageCache *__imageCache = nil;
-static dispatch_queue_t __imageCacheDispatchQueue = NULL;
 
 #pragma mark - Object Lifecycle
 
@@ -68,15 +67,19 @@ + (instancetype)sharedImageCache {
     return __imageCache;
 }
 
++ (dispatch_queue_t)dispatchQueue {
+    static dispatch_queue_t __imageCacheDispatchQueue = NULL;
+    static dispatch_once_t onceToken;
+    dispatch_once(&onceToken, ^{
+        __imageCacheDispatchQueue = dispatch_queue_create("com.path.FastImageCacheQueue", NULL);
+    });
+    return __imageCacheDispatchQueue;
+}
+
 - (id)init {
     self = [super init];
 
     if (self != nil) {
-        static dispatch_once_t onceToken;
-        dispatch_once(&onceToken, ^{
-            __imageCacheDispatchQueue = dispatch_queue_create("com.path.FastImageCacheQueue", NULL);
-        });
-        
         _formats = [[NSMutableDictionary alloc] init];
         _imageTables = [[NSMutableDictionary alloc] init];
         _requests = [[NSMutableDictionary alloc] init];
@@ -159,7 +162,7 @@ - (BOOL)_retrieveImageForEntity:(id <FICEntity>)entity withFormatName:(NSString
     if (loadSynchronously == NO && [imageTable entryExistsForEntityUUID:entityUUID sourceImageUUID:sourceImageUUID]) {
         imageExists = YES;
 
-        dispatch_async(__imageCacheDispatchQueue, ^{
+        dispatch_async([FICImageCache dispatchQueue], ^{
             UIImage *image = [imageTable newImageForEntityUUID:entityUUID sourceImageUUID:sourceImageUUID];
 
             if (completionBlock != nil) {
@@ -332,7 +335,7 @@ - (void)_processImage:(UIImage *)image forEntity:(id <FICEntity>)entity imageTab
         NSString *imageFormatName = [imageFormat name];
         FICEntityImageDrawingBlock imageDrawingBlock = [entity drawingBlockForImage:image withFormatName:imageFormatName];
 
-        dispatch_async(__imageCacheDispatchQueue, ^{
+        dispatch_async([FICImageCache dispatchQueue], ^{
             [imageTable setEntryForEntityUUID:entityUUID sourceImageUUID:sourceImageUUID imageDrawingBlock:imageDrawingBlock];
 
             UIImage *resultImage = [imageTable newImageForEntityUUID:entityUUID sourceImageUUID:sourceImageUUID];

FastImageCache/FICImageTableEntry.m

@@ -77,7 +77,7 @@ - (void)executeBlockOnDealloc:(dispatch_block_t)block {
 
 - (void)dealloc {
     for (dispatch_block_t block in _deallocBlocks) {
-        block();
+        dispatch_async([FICImageCache dispatchQueue], block);
     }
 }