Fix race condition with SDWebImageManager's cancelForDelegate:

The -cancelForDelegate: method was working for downloads but not local cache checks. Add some new machinery to keep track of pending cache requests and only message the delegate if it hasn't since requested cancellation.

SDWebImageManager.h

@@ -13,8 +13,9 @@
 
 @interface SDWebImageManager : NSObject <SDWebImageDownloaderDelegate, SDImageCacheDelegate>
 {
-    NSMutableArray *delegates;
+    NSMutableArray *downloadDelegates;
     NSMutableArray *downloaders;
+    NSMutableArray *cacheDelegates;
     NSMutableDictionary *downloaderForURL;
     NSMutableArray *failedURLs;
 }

SDWebImageManager.m

@@ -18,8 +18,9 @@ static SDWebImageManager *instance;
 {
     if ((self = [super init]))
     {
-        delegates = [[NSMutableArray alloc] init];
+        downloadDelegates = [[NSMutableArray alloc] init];
         downloaders = [[NSMutableArray alloc] init];
+        cacheDelegates = [[NSMutableArray alloc] init];
         downloaderForURL = [[NSMutableDictionary alloc] init];
         failedURLs = [[NSMutableArray alloc] init];
     }
@@ -28,8 +29,9 @@ static SDWebImageManager *instance;
 
 - (void)dealloc
 {
-    [delegates release], delegates = nil;
+    [downloadDelegates release], downloadDelegates = nil;
     [downloaders release], downloaders = nil;
+    [cacheDelegates release], cacheDelegates = nil;
     [downloaderForURL release], downloaderForURL = nil;
     [failedURLs release], failedURLs = nil;
     [super dealloc];
@@ -72,32 +74,34 @@ static SDWebImageManager *instance;
     }
 
     // Check the on-disk cache async so we don't block the main thread
+    [cacheDelegates addObject:delegate];
     NSDictionary *info = [NSDictionary dictionaryWithObjectsAndKeys:delegate, @"delegate", url, @"url", [NSNumber numberWithBool:lowPriority], @"low_priority", nil];
     [[SDImageCache sharedImageCache] queryDiskCacheForKey:[url absoluteString] delegate:self userInfo:info];
 }
 
 - (void)cancelForDelegate:(id<SDWebImageManagerDelegate>)delegate
 {
-    NSUInteger idx = [delegates indexOfObjectIdenticalTo:delegate];
+    // Remove all instances of delegate from cacheDelegates.
+    // (removeObjectIdenticalTo: does this, despite its singular name.)
+    [cacheDelegates removeObjectIdenticalTo:delegate];
 
-    if (idx == NSNotFound)
+    NSUInteger idx;
+    while ((idx = [downloadDelegates indexOfObjectIdenticalTo:delegate]) != NSNotFound)
     {
-        return;
+        SDWebImageDownloader *downloader = [[downloaders objectAtIndex:idx] retain];
+
+        [downloadDelegates removeObjectAtIndex:idx];
+        [downloaders removeObjectAtIndex:idx];
+
+        if (![downloaders containsObject:downloader])
+        {
+            // No more delegate are waiting for this download, cancel it
+            [downloader cancel];
+            [downloaderForURL removeObjectForKey:downloader.url];
+        }
+
+        [downloader release];
     }
-
-    SDWebImageDownloader *downloader = [[downloaders objectAtIndex:idx] retain];
-
-    [delegates removeObjectAtIndex:idx];
-    [downloaders removeObjectAtIndex:idx];
-
-    if (![downloaders containsObject:downloader])
-    {
-        // No more delegate are waiting for this download, cancel it
-        [downloader cancel];
-        [downloaderForURL removeObjectForKey:downloader.url];
-    }
-
-    [downloader release];
 }
 
 #pragma mark SDImageCacheDelegate
@@ -105,10 +109,23 @@ static SDWebImageManager *instance;
 - (void)imageCache:(SDImageCache *)imageCache didFindImage:(UIImage *)image forKey:(NSString *)key userInfo:(NSDictionary *)info
 {
     id<SDWebImageManagerDelegate> delegate = [info objectForKey:@"delegate"];
+
+    NSUInteger idx = [cacheDelegates indexOfObjectIdenticalTo:delegate];
+    if (idx == NSNotFound)
+    {
+        // Request has since been canceled
+        return;
+    }
+
     if ([delegate respondsToSelector:@selector(webImageManager:didFinishWithImage:)])
     {
         [delegate performSelector:@selector(webImageManager:didFinishWithImage:) withObject:self withObject:image];
     }
+
+    // Remove one instance of delegate from the array,
+    // not all of them (as |removeObjectIdenticalTo:| would)
+    // in case multiple requests are issued.
+    [cacheDelegates removeObjectAtIndex:idx];
 }
 
 - (void)imageCache:(SDImageCache *)imageCache didNotFindImageForKey:(NSString *)key userInfo:(NSDictionary *)info
@@ -117,6 +134,15 @@ static SDWebImageManager *instance;
     id<SDWebImageManagerDelegate> delegate = [info objectForKey:@"delegate"];
     BOOL lowPriority = [[info objectForKey:@"low_priority"] boolValue];
 
+    NSUInteger idx = [cacheDelegates indexOfObjectIdenticalTo:delegate];
+    if (idx == NSNotFound)
+    {
+        // Request has since been canceled
+        return;
+    }
+
+    [cacheDelegates removeObjectAtIndex:idx];
+
     // Share the same downloader for identical URLs so we don't download the same URL several times
     SDWebImageDownloader *downloader = [downloaderForURL objectForKey:url];
 
@@ -132,7 +158,7 @@ static SDWebImageManager *instance;
         downloader.lowPriority = NO;
     }
 
-    [delegates addObject:delegate];
+    [downloadDelegates addObject:delegate];
     [downloaders addObject:downloader];
 }
 
@@ -142,14 +168,14 @@ static SDWebImageManager *instance;
 {
     [downloader retain];
 
-    // Notify all the delegates with this downloader
+    // Notify all the downloadDelegates with this downloader
     for (NSInteger idx = (NSInteger)[downloaders count] - 1; idx >= 0; idx--)
     {
         NSUInteger uidx = (NSUInteger)idx;
         SDWebImageDownloader *aDownloader = [downloaders objectAtIndex:uidx];
         if (aDownloader == downloader)
         {
-            id<SDWebImageManagerDelegate> delegate = [delegates objectAtIndex:uidx];
+            id<SDWebImageManagerDelegate> delegate = [downloadDelegates objectAtIndex:uidx];
 
             if (image)
             {
@@ -167,7 +193,7 @@ static SDWebImageManager *instance;
             }
 
             [downloaders removeObjectAtIndex:uidx];
-            [delegates removeObjectAtIndex:uidx];
+            [downloadDelegates removeObjectAtIndex:uidx];
         }
     }
 
@@ -195,14 +221,14 @@ static SDWebImageManager *instance;
 {
     [downloader retain];
 
-    // Notify all the delegates with this downloader
+    // Notify all the downloadDelegates with this downloader
     for (NSInteger idx = (NSInteger)[downloaders count] - 1; idx >= 0; idx--)
     {
         NSUInteger uidx = (NSUInteger)idx;
         SDWebImageDownloader *aDownloader = [downloaders objectAtIndex:uidx];
         if (aDownloader == downloader)
         {
-            id<SDWebImageManagerDelegate> delegate = [delegates objectAtIndex:uidx];
+            id<SDWebImageManagerDelegate> delegate = [downloadDelegates objectAtIndex:uidx];
 
             if ([delegate respondsToSelector:@selector(webImageManager:didFailWithError:)])
             {
@@ -210,7 +236,7 @@ static SDWebImageManager *instance;
             }
 
             [downloaders removeObjectAtIndex:uidx];
-            [delegates removeObjectAtIndex:uidx];
+            [downloadDelegates removeObjectAtIndex:uidx];
         }
     }