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Use dispatch_barrier to handle NSMutableDictionary thread unsafety instead of main thread dispatching

This commit is contained in:
Olivier Poitrey 2012-11-06 03:31:03 +01:00
parent 13210a6925
commit 570965f6cf
1 changed files with 73 additions and 57 deletions
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88
SDWebImage/SDWebImageDownloader.m
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@ -20,6 +20,7 @@ NSString *const kCompletedCallbackKey = @"completed";
@property (strong, nonatomic) NSOperationQueue *downloadQueue;
@property (strong, nonatomic) NSMutableDictionary *URLCallbacks;
@property (assign, nonatomic) dispatch_queue_t barrierQueue;
@end
@ -65,6 +66,7 @@ NSString *const kCompletedCallbackKey = @"completed";
_downloadQueue = NSOperationQueue.new;
_downloadQueue.maxConcurrentOperationCount = 10;
_URLCallbacks = NSMutableDictionary.new;
_barrierQueue = dispatch_queue_create("com.hackemist.SDWebImageDownloaderBarrierQueue", DISPATCH_QUEUE_CONCURRENT);
}
return self;
}
@ -82,28 +84,9 @@ NSString *const kCompletedCallbackKey = @"completed";
- (NSOperation *)downloadImageWithURL:(NSURL *)url options:(SDWebImageDownloaderOptions)options progress:(void (^)(NSUInteger, long long))progressBlock completed:(void (^)(UIImage *, NSError *, BOOL))completedBlock
{
__block SDWebImageDownloaderOperation *operation;
__weak SDWebImageDownloader *wself = self;
dispatch_async(dispatch_get_main_queue(), ^ // NSDictionary isn't thread safe
{
BOOL performDownload = NO;
if (!self.URLCallbacks[url])
{
self.URLCallbacks[url] = NSMutableArray.new;
performDownload = YES;
}
// Handle single download of simultaneous download request for the same URL
{
NSMutableArray *callbacksForURL = self.URLCallbacks[url];
NSMutableDictionary *callbacks = NSMutableDictionary.new;
if (progressBlock) callbacks[kProgressCallbackKey] = progressBlock;
if (completedBlock) callbacks[kCompletedCallbackKey] = completedBlock;
[callbacksForURL addObject:callbacks];
self.URLCallbacks[url] = callbacksForURL;
}
if (performDownload)
[self addProgressCallback:progressBlock andCompletedBlock:completedBlock forURL:url createCallback:^
{
// In order to prevent from potential duplicate caching (NSURLCache + SDImageCache) we disable the cache for image requests
NSMutableURLRequest *request = [NSMutableURLRequest.alloc initWithURL:url cachePolicy:NSURLCacheStorageNotAllowed timeoutInterval:15];
@ -112,41 +95,74 @@ NSString *const kCompletedCallbackKey = @"completed";
[request addValue:@"image/*" forHTTPHeaderField:@"Accept"];
operation = [SDWebImageDownloaderOperation.alloc initWithRequest:request options:options progress:^(NSUInteger receivedSize, long long expectedSize)
{
dispatch_async(dispatch_get_main_queue(), ^
{
NSMutableArray *callbacksForURL = self.URLCallbacks[url];
if (!wself) return;
SDWebImageDownloader *sself = wself;
NSArray *callbacksForURL = [sself removeAndReturnCallbacksForURL:url];
for (NSDictionary *callbacks in callbacksForURL)
{
SDWebImageDownloaderProgressBlock callback = callbacks[kProgressCallbackKey];
if (callback) callback(receivedSize, expectedSize);
}
});
}
completed:^(UIImage *image, NSError *error, BOOL finished)
{
dispatch_async(dispatch_get_main_queue(), ^
{
NSMutableArray *callbacksForURL = self.URLCallbacks[url];
[self.URLCallbacks removeObjectForKey:url];
if (!wself) return;
SDWebImageDownloader *sself = wself;
NSArray *callbacksForURL = [sself removeAndReturnCallbacksForURL:url];
for (NSDictionary *callbacks in callbacksForURL)
{
SDWebImageDownloaderCompletedBlock callback = callbacks[kCompletedCallbackKey];
if (callback) callback(image, error, finished);
}
});
}
cancelled:^
{
dispatch_async(dispatch_get_main_queue(), ^
{
[self.URLCallbacks removeObjectForKey:url];
});
if (!wself) return;
SDWebImageDownloader *sself = wself;
[sself removeAndReturnCallbacksForURL:url];
}];
[self.downloadQueue addOperation:operation];
}
});
}];
return operation;
}
- (void)addProgressCallback:(void (^)(NSUInteger, long long))progressBlock andCompletedBlock:(void (^)(UIImage *, NSError *, BOOL))completedBlock forURL:(NSURL *)url createCallback:(void (^)())createCallback
{
dispatch_barrier_async(self.barrierQueue, ^
{
BOOL first = NO;
if (!self.URLCallbacks[url])
{
self.URLCallbacks[url] = NSMutableArray.new;
first = YES;
}
// Handle single download of simultaneous download request for the same URL
NSMutableArray *callbacksForURL = self.URLCallbacks[url];
NSMutableDictionary *callbacks = NSMutableDictionary.new;
if (progressBlock) callbacks[kProgressCallbackKey] = progressBlock;
if (completedBlock) callbacks[kCompletedCallbackKey] = completedBlock;
[callbacksForURL addObject:callbacks];
self.URLCallbacks[url] = callbacksForURL;
if (first)
{
createCallback();
}
});
}
- (NSArray *)removeAndReturnCallbacksForURL:(NSURL *)url
{
__block NSArray *callbacksForURL;
dispatch_barrier_sync(self.barrierQueue, ^
{
callbacksForURL = self.URLCallbacks[url];
[self.URLCallbacks removeObjectForKey:url];
});
return callbacksForURL;
}
@end