potentially problem when system load high: #79

YYWebImage/Categories/CALayer+YYWebImage.m

@@ -146,7 +146,7 @@ static int _YYWebImageSetterKey;
             };
             
             __block int32_t newSentinel = 0;
-            __weak typeof(setter) weakSetter = nil;
+            __block __weak typeof(setter) weakSetter = nil;
             YYWebImageCompletionBlock _completion = ^(UIImage *image, NSURL *url, YYWebImageFromType from, YYWebImageStage stage, NSError *error) {
                 __strong typeof(_self) self = _self;
                 BOOL setImage = (stage == YYWebImageStageFinished || stage == YYWebImageStageProgress) && image && !(options & YYWebImageOptionAvoidSetImage);

YYWebImage/Categories/MKAnnotationView+YYWebImage.m

@@ -146,7 +146,7 @@ static int _YYWebImageSetterKey;
             };
             
             __block int32_t newSentinel = 0;
-            __weak typeof(setter) weakSetter = nil;
+            __block __weak typeof(setter) weakSetter = nil;
             YYWebImageCompletionBlock _completion = ^(UIImage *image, NSURL *url, YYWebImageFromType from, YYWebImageStage stage, NSError *error) {
                 __strong typeof(_self) self = _self;
                 BOOL setImage = (stage == YYWebImageStageFinished || stage == YYWebImageStageProgress) && image && !(options & YYWebImageOptionAvoidSetImage);

YYWebImage/Categories/UIButton+YYWebImage.m

@@ -134,7 +134,7 @@ static int _YYWebImageBackgroundSetterKey;
             };
             
             __block int32_t newSentinel = 0;
-            __weak typeof(setter) weakSetter = nil;
+            __block __weak typeof(setter) weakSetter = nil;
             YYWebImageCompletionBlock _completion = ^(UIImage *image, NSURL *url, YYWebImageFromType from, YYWebImageStage stage, NSError *error) {
                 __strong typeof(_self) self = _self;
                 BOOL setImage = (stage == YYWebImageStageFinished || stage == YYWebImageStageProgress) && image && !(options & YYWebImageOptionAvoidSetImage);
@@ -315,7 +315,7 @@ static int _YYWebImageBackgroundSetterKey;
             };
             
             __block int32_t newSentinel = 0;
-            __weak typeof(setter) weakSetter = nil;
+            __block __weak typeof(setter) weakSetter = nil;
             YYWebImageCompletionBlock _completion = ^(UIImage *image, NSURL *url, YYWebImageFromType from, YYWebImageStage stage, NSError *error) {
                 __strong typeof(_self) self = _self;
                 BOOL setImage = (stage == YYWebImageStageFinished || stage == YYWebImageStageProgress) && image && !(options & YYWebImageOptionAvoidSetImage);

YYWebImage/Categories/UIImageView+YYWebImage.m

@@ -150,7 +150,7 @@ static int _YYWebImageHighlightedSetterKey;
             };
             
             __block int32_t newSentinel = 0;
-            __weak typeof(setter) weakSetter = nil;
+            __block __weak typeof(setter) weakSetter = nil;
             YYWebImageCompletionBlock _completion = ^(UIImage *image, NSURL *url, YYWebImageFromType from, YYWebImageStage stage, NSError *error) {
                 __strong typeof(_self) self = _self;
                 BOOL setImage = (stage == YYWebImageStageFinished || stage == YYWebImageStageProgress) && image && !(options & YYWebImageOptionAvoidSetImage);
@@ -314,7 +314,7 @@ static int _YYWebImageHighlightedSetterKey;
             };
             
             __block int32_t newSentinel = 0;
-            __weak typeof(setter) weakSetter = nil;
+            __block __weak typeof(setter) weakSetter = nil;
             YYWebImageCompletionBlock _completion = ^(UIImage *image, NSURL *url, YYWebImageFromType from, YYWebImageStage stage, NSError *error) {
                 __strong typeof(_self) self = _self;
                 BOOL setImage = (stage == YYWebImageStageFinished || stage == YYWebImageStageProgress) && image && !(options & YYWebImageOptionAvoidSetImage);