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Fix the LIFO execute order issue, we should make all previous operation dependent the new operation, Foundation will take care of dependency graph and calculate the order

This commit is contained in:
DreamPiggy 2019-09-26 22:47:09 +08:00
parent 902c619126
commit 76a6beb029
1 changed files with 6 additions and 4 deletions
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10
SDWebImage/Core/SDWebImageDownloader.m
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@ -38,7 +38,6 @@ static void * SDWebImageDownloaderContext = &SDWebImageDownloaderContext;
@interface SDWebImageDownloader () <NSURLSessionTaskDelegate, NSURLSessionDataDelegate>
@property (strong, nonatomic, nonnull) NSOperationQueue *downloadQueue;
@property (weak, nonatomic, nullable) NSOperation *lastAddedOperation;
@property (strong, nonatomic, nonnull) NSMutableDictionary<NSURL *, NSOperation<SDWebImageDownloaderOperation> *> *URLOperations;
@property (strong, nonatomic, nullable) NSMutableDictionary<NSString *, NSString *> *HTTPHeaders;
@property (strong, nonatomic, nonnull) dispatch_semaphore_t HTTPHeadersLock; // A lock to keep the access to `HTTPHeaders` thread-safe
@ -321,9 +320,12 @@ static void * SDWebImageDownloaderContext = &SDWebImageDownloaderContext;
}
if (self.config.executionOrder == SDWebImageDownloaderLIFOExecutionOrder) {
// Emulate LIFO execution order by systematically adding new operations as last operation's dependency
[self.lastAddedOperation addDependency:operation];
self.lastAddedOperation = operation;
// Emulate LIFO execution order by systematically, each previous adding operation can dependency the new operation
// This can gurantee the new operation to be execulated firstly, even if when some operations finished, meanwhile you appending new operations
// Just make last added operation dependents new operation can not solve this problem. See test case #test15DownloaderLIFOExecutionOrder
for (NSOperation *pendingOperation in self.downloadQueue.operations) {
[pendingOperation addDependency:operation];
}
}
return operation;