Race condition causes imageData to be nil

[bpoplauschi]

Thanks to @jdelStrother for this:

Comment 1:

For what it's worth, I ran into this crash on 3.7.0, while rapidly scrolling a tableview containing UIImageViews, each of which was requesting a load from SDWebImage. I ended up at this stack trace :

#0  0x000000010e571f9f in CFRelease ()
#1  0x000000010a499d02 in +[UIImage(MultiFormat) sd_imageOrientationFromImageData:] at /Users/jon/Developer/iphone/Pods/SDWebImage/SDWebImage/UIImage+MultiFormat.m:63
#2  0x000000010a499b20 in +[UIImage(MultiFormat) sd_imageWithData:] at /Users/jon/Developer/iphone/Pods/SDWebImage/SDWebImage/UIImage+MultiFormat.m:34
#3  0x000000010a489960 in -[SDWebImageDownloaderOperation connectionDidFinishLoading:] at /Users/jon/Developer/iphone/Pods/SDWebImage/SDWebImage/SDWebImageDownloaderOperation.m:343
#4  0x000000010b5e536b in __65-[NSURLConnectionInternal _withConnectionAndDelegate:onlyActive:]_block_invoke ()
#5  0x000000010b498bdb in -[NSURLConnectionInternal _withConnectionAndDelegate:onlyActive:] ()
#6  0x000000010b498aec in -[NSURLConnectionInternal _withActiveConnectionAndDelegate:] ()
#7  0x000000010e381637 in ___ZN27URLConnectionClient_Classic26_delegate_didFinishLoadingEU13block_pointerFvvE_block_invoke ()
#8  0x000000010e37f802 in ___ZN27URLConnectionClient_Classic18_withDelegateAsyncEPKcU13block_pointerFvP16_CFURLConnectionPK33CFURLConnectionClientCurrent_VMaxE_block_invoke_2 ()
#9  0x000000010e590f74 in CFArrayApplyFunction ()
#10 0x000000010e2f23e7 in RunloopBlockContext::perform() ()
#11 0x000000010e2f2217 in MultiplexerSource::perform() ()
#12 0x000000010e2f203a in MultiplexerSource::_perform(void*) ()
#13 0x000000010e579d21 in __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ ()
#14 0x000000010e5795f2 in __CFRunLoopDoSources0 ()
#15 0x000000010e59546f in __CFRunLoopRun ()
#16 0x000000010e594d83 in CFRunLoopRunSpecific ()
#17 0x000000010e59f8c1 in CFRunLoopRun ()
#18 0x000000010a487651 in -[SDWebImageDownloaderOperation start] at /Users/jon/Developer/iphone/Pods/SDWebImage/SDWebImage/SDWebImageDownloaderOperation.m:103
#19 0x000000010b56cc0b in __NSOQSchedule_f ()
#20 0x000000010f8e072d in _dispatch_client_callout ()
#21 0x000000010f8ceeab in _dispatch_async_redirect_invoke ()
#22 0x000000010f8e072d in _dispatch_client_callout ()
#23 0x000000010f8d0b27 in _dispatch_root_queue_drain ()
#24 0x000000010f8d0d12 in _dispatch_worker_thread2 ()
#25 0x000000010fc7cef8 in _pthread_wqthread ()
#26 0x000000010fc7ffb9 in start_wqthread ()

By this point, self.imageData was nil, which is why imageSource ended up as NULL. self.expectedSize was set, however, so didReceiveResponse presumably got called.

Is it a race condition where one thread finishes downloading & calls connectionDidFinishLoading, and then another thread calls reset ?

Comment 2:

Actually, I can reproduce this pretty easily if I put a sleep(1) in connectionDidFinishLoading to exaggerate the race condition, and repeatedly calling sd_setImageWithURL from the main thread.

Possibly connectionDidFinishLoading should take a reference to imageData at the start (like it does with completionBlock), and bail if either are nil? Even that might not be sufficient though - is it ok calling done (and thus reset) at the end of connectionDidFinishLoading, when the main thread might have tried to start a new image loading in the middle of that method?

Comment 3:

Yeah, 3.7.1 fixes the crash, though you get ImageIO: CGImageSourceCreateWithData data parameter is nil in the log. Still slightly concerned about race conditions in the latter half of connectionDidFinishLoading, but I can't reproduce any problems with it.

[bpoplauschi]

Problem originally discussed in #764

[rsanchezsaez]

I think this is also related to #847, as I believe that one is also because of racing conditions.

Sorry to say but SDWebImage 3.7.1 is really buggy... :-(

[bpoplauschi]

So I say, let's fix it :)

[nishan-guiddit]

@bpoplauschi has this issue been fixed. I'm facing the same problem as I'm trying to load the images in the Tableview. Application gets crashed and below error log is got

": ImageIO: CGImageSourceCreateWithData data parameter is nil "

Can you please let me know how this can be solved ?

[kiddtaurus]

@bpoplauschi Whether the bug has be fixed in release 3.7.3?

[bpoplauschi]

Should be fixed in the latest 4.x branch. Should revisit after 4.0 is released.