Merge branch 'master' of github.com:rs/SDWebImage

@@ -193,7 +193,7 @@ Common Problems
 
 
 ### Using dynamic image size with UITableViewCell
 ### Using dynamic image size with UITableViewCell
 
 
-UITableView determins the size of the image by the first image set for a cell. If your remote images
+UITableView determines the size of the image by the first image set for a cell. If your remote images
 don't have the same size as your placeholder image, you may experience strange anamorphic scaling issue.
 don't have the same size as your placeholder image, you may experience strange anamorphic scaling issue.
 The following article gives a way to workaround this issue:
 The following article gives a way to workaround this issue:
 
 

@@ -48,7 +48,6 @@ BOOL ImageDataHasPNGPreffix(NSData *data) {
     static id instance;
     static id instance;
     dispatch_once(&once, ^{
     dispatch_once(&once, ^{
         instance = [self new];
         instance = [self new];
-        kPNGSignatureData = [NSData dataWithBytes:kPNGSignatureBytes length:8];
     });
     });
     return instance;
     return instance;
 }
 }
@@ -61,6 +60,9 @@ BOOL ImageDataHasPNGPreffix(NSData *data) {
     if ((self = [super init])) {
     if ((self = [super init])) {
         NSString *fullNamespace = [@"com.hackemist.SDWebImageCache." stringByAppendingString:ns];
         NSString *fullNamespace = [@"com.hackemist.SDWebImageCache." stringByAppendingString:ns];
 
 
+        // initialise PNG signature data
+        kPNGSignatureData = [NSData dataWithBytes:kPNGSignatureBytes length:8];
+
         // Create IO serial queue
         // Create IO serial queue
         _ioQueue = dispatch_queue_create("com.hackemist.SDWebImageCache", DISPATCH_QUEUE_SERIAL);
         _ioQueue = dispatch_queue_create("com.hackemist.SDWebImageCache", DISPATCH_QUEUE_SERIAL);
 
 

@@ -194,7 +194,9 @@
 
 
                     if (error.code != NSURLErrorNotConnectedToInternet && error.code != NSURLErrorCancelled && error.code != NSURLErrorTimedOut) {
                     if (error.code != NSURLErrorNotConnectedToInternet && error.code != NSURLErrorCancelled && error.code != NSURLErrorTimedOut) {
                         @synchronized (self.failedURLs) {
                         @synchronized (self.failedURLs) {
-                            [self.failedURLs addObject:url];
+                            if (![self.failedURLs containsObject:url]) {
+                                [self.failedURLs addObject:url];
+                            }
                         }
                         }
                     }
                     }
                 }
                 }