iOS Player crashes when Dispose() is called on WWW instance (Unity 5.3.4f1)

Unity iOS player crashes when Dispose() is called in specific moments of a download (LoadFromCacheOrDownload()). We've noticed that if you have a good wifi and Internet connection then the download progress just grows steadily. During this steady download there are moments of hiccups - download progress seems to pause for a while (from a fraction of second to a few seconds) and if Dispose() is called then - it crashes. Crash logs indicate it's something with threads data synchronization.

Our game quite frequently needs to cancel asset bundle download so crashes happen from time to time (or pretty frequently if network is fast and you know when to call Dispose(). We've also checked uncached download using new WWW() but it's the same. Due to this issue the WWW class is useless for us and we're now implementing our own download and simple caching system.

Bug is on issue tracker:
https://goo.gl/FMuibb

Any piece of advice on how to "fix" this issue is welcomed.

 

We'll also test UnityWebRequest - maybe it won't crash.

 

We've tried UnityWebRequest but unfortunately it also crashes when Abort() is called right after the download starts. Bug report:
https://goo.gl/fgJ029
Additionally Abort() on iOS may produce invalid error value:
https://goo.gl/KR3xWJ

 

Great! If you need any additional info please let me know.

 

We're seeing something similar to this on 5.3.5p2 right now ( iOS )

*On 5.3.4p1 we never saw this, in fact 5.3.4p1 was pretty darn stable. 5.3.5x seems to be more unstable.

 

5.3.5p2 same problem here.
5.3.5f1 is fine for me.
This problem occurs only on iOS. Android is fine.

Code (CSharp):

1.  
2.     public static IEnumerator WWW(string url, byte[] value, Action<WWW> onDone)
3.     {
4.         var isFinish = false;
5.  
6.         while (isFinish == false)
7.         {
8.             var www = new WWW(url, value);
9.  
10.             yield return WWWInternal(www, (innerWww) =>
11.             {
12.                 isFinish = true;
13.                 onDone(innerWww);
14.             });
15.         }
16.     }
17.  
18.     public static IEnumerator WWWInternal(WWW www, Action<WWW> onDone)
19.     {
20.         yield return SomeTimeoutProcess(www);
21.  
22.         if (www.isDone && www.error == null)
23.         {
24.             onDone(www);
25.         }
26.         else
27.         {
28.             yield return SomeFailedProcess();
29.         }
30.      
31.         // www.Dispose();
32.     }
33.  

If I execute commented www.Dispose(), application always crash.

here is crash report.
=================================================================================
Hardware Model: iPhone7,1
Code Type: ARM-64 (Native)

Date/Time: 2016-06-04 17:52:36.36 +0900
Launch Time: 2016-06-04 17:52:28.28 +0900
OS Version: iOS 9.3.1 (13E238)
Report Version: 105

Exception Type: EXC_CRASH (SIGSEGV)
Exception Codes: 0x0000000000000000, 0x0000000000000000
Exception Note: EXC_CORPSE_NOTIFY
Triggered by Thread: 1

Filtered syslog:
None found

Breadcrumb Trail: (reverse chronological seconds)
1 GC Framework: startAuthenticationForExistingPrimaryPlayer

Thread 0 name: Dispatch queue: com.apple.main-thread
Thread 0:
0 libsystem_kernel.dylib 0x0000000180d9f7ec __kill + 8
1 libsystem_platform.dylib 0x0000000180e6594c _sigtramp + 68
2 rb 0x0000000100e479d8 TransportiPhone::Abort() (TransportiPhone.cpp:28)
3 rb 0x0000000100e57edc WWW_CUSTOM_DestroyWWW(ScriptingObjectWithIntPtrField<WWW>, unsigned char) (UtilsBindings.gen.cpp:85)
4 rb 0x000000010015ddc0 U3CWWWInternalU3Ec__Iterator7_MoveNext_m3509145728 (Bulk_Assembly-CSharp_2.cpp:1933)
5 rb 0x00000001007692d8 SetupCoroutine_InvokeMoveNext_m3556339879 (Bulk_UnityEngine_2.cpp:5489)
6 rb 0x0000000100a38a88 RuntimeInvoker_Void_t2779279689_Il2CppObject_IntPtr_t(MethodInfo const*, void*, void**) (Il2CppInvokerTable.cpp:2639)
7 rb 0x0000000101326ba8 il2cpp::vm::Runtime::Invoke(MethodInfo const*, void*, void**, Il2CppException**) (Runtime.cpp:363)
8 rb 0x0000000100c3be20 ScriptingInvocation::Invoke(ScriptingException**, bool) (ScriptingInvocation.cpp:180)
9 rb 0x0000000100c2ef90 Coroutine::InvokeMoveNext(ScriptingException**) (Coroutine.cpp:203)
10 rb 0x0000000100c2ecfc Coroutine::Run() (Coroutine.cpp:228)
11 rb 0x0000000100c2ed54 Coroutine::Run() (Coroutine.cpp:259)
12 rb 0x0000000100c2ed54 Coroutine::Run() (Coroutine.cpp:259)
13 rb 0x0000000100b08fc4 DelayedCallManager::Update(int) (CallDelayed.cpp:178)
14 rb 0x0000000100becdac PlayerLoop(bool, bool, IHookEvent*) (Player.cpp:1721)
15 rb 0x0000000100e6b3f4 UnityPlayerLoopImpl(bool) (LibEntryPoint.mm:240)
16 rb 0x00000001000eabe8 UnityRepaint (UnityAppController+Rendering.mm:238)
17 rb 0x00000001000fb4f0 -[UnityAppController(ViewHandling) showGameUI] (UnityAppController+ViewHandling.mm:212)
18 rb 0x00000001000f8090 -[UnityAppController startUnity (UnityAppController.mm:126)
19 Foundation 0x0000000181bce628 __NSFireDelayedPerform + 428
20 CoreFoundation 0x00000001811bd81c __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 28
21 CoreFoundation 0x00000001811bd4c0 __CFRunLoopDoTimer + 884
22 CoreFoundation 0x00000001811babd4 __CFRunLoopRun + 1520
23 CoreFoundation 0x00000001810e4d10 CFRunLoopRunSpecific + 384
24 GraphicsServices 0x00000001829cc088 GSEventRunModal + 180
25 UIKit 0x00000001863b9f70 UIApplicationMain + 204
26 rb 0x00000001000e496c main (main.mm:32)
27 libdyld.dylib 0x0000000180c828b8 start + 4

Thread 1 name: Dispatch queue: com.apple.gamecenter.GKDaemonProxy
Thread 1 Crashed:
0 libsystem_kernel.dylib 0x0000000180d85014 semaphore_wait_trap + 8
1 libdispatch.dylib 0x0000000180c628c4 _dispatch_group_wait_slow + 260
2 GameCenterFoundation 0x000000018f2f7a6c __36-[GKServiceProxy buildServiceLookup]_block_invoke + 752
3 libdispatch.dylib 0x0000000180c514bc _dispatch_call_block_and_release + 24
4 libdispatch.dylib 0x0000000180c5147c _dispatch_client_callout + 16
5 libdispatch.dylib 0x0000000180c5d4c0 _dispatch_queue_drain + 864
6 libdispatch.dylib 0x0000000180c54f80 _dispatch_queue_invoke + 464
7 libdispatch.dylib 0x0000000180c5147c _dispatch_client_callout + 16
8 libdispatch.dylib 0x0000000180c5f914 _dispatch_root_queue_drain + 2140
9 libdispatch.dylib 0x0000000180c5f0b0 _dispatch_worker_thread3 + 112
10 libsystem_pthread.dylib 0x0000000180e69470 _pthread_wqthread + 1092
11 libsystem_pthread.dylib 0x0000000180e69020 start_wqthread + 4

 

I can confirm too that WWW.Dispose() crashes on iOS with Unity 5.3.5p2 but not with 5.3.5.p1.

 

@christophergoy I reported 803333 now. Thanks. Good Luck!

 

We have the same error when calling WWW.Dispose to terminate a ongoing download of an AssetBundle.

The crash typically occurs only after 20-30% of the download has completed (in our case after downloading 6-9MB).

Calling WWW.Dispose shortly after the download begins does not cause the app to crash.

Code works fine in Editor. Bug is only in iOS.

Error occurs on both Unity 5.3.5p1 and p2.

 

A correction to earlier post : the pattern for crashing seems to be the rate at which the download is progressing; seems to be some sort of race condition on the file handle.

 

Yes. my Crash would occur during the download of AssetBundle.

 

Just a theory but this crash might happen during streamed data decompression - while decompression thread decompresses stream data, the Dispose() is called on the main thread which invalidates streamed data pointers (or data itself) causing the compression thread to read/write invalid data (pointers). It may be the case that default unity behavior which is recompressing LZMA into LZ4 on the fly causes this issue. Unfortunately I don't have time to test this but recompression can be disabled using Caching.compressionEnabled (default is true). This will result in longer asset budles loading time. Docs on asset bundle compression: http://docs.unity3d.com/Manual/AssetBundleCompression.html

 

Also you can avoid decompression while using LZ4 when building the asset bundles - the recompression shouldn't take place but you'll get larger files to download.

 

Do you know if it's fixed on 5.3.5p3? Basically it is a breaking change for us.

 

I'm not sure if this is related, but I'm actually getting the issue (or a similar one) in 5.3.5p4, but not in previous versions (5.3.5p3 and 5.3.5p2, specifically). The only difference on my end is that I'm using UnityWebRequest, not WWW. I've created a bug report (807366). Are these two classes not using the same underlying codebase?

 

In 5.3.5p2, we used WebRequest.Dispose to get around the crash on Dispose. However, there's an issue with detecting network failures.
We observed that if the network is disconnected while WebRequest is downloading content, it falsely reports the download is a success. We have no such problems with WWW.

 

Thanks for looking into it, Its actually business critical for us since our game is live on the store and we are having a lot of complaints about crashes. We are using UnityWebRequest and still observing crash on all iOS devices (many different iOS versions too) : bug report https://fogbugz.unity3d.com/default.asp?807267_ek5huu9brode5fgl
forum post with crash details : http://forum.unity3d.com/threads/il2cpp-ios-crash-exc_bad_access-using-unitywebrequest.412214/

 

@christophergoy hi ! Sorry for pinging you out but we saw that a new Unity patch (5.3.5p5) got just released, does't it fix the networking ios crash issues ? (its not really pointed out in the patch notes).

Thanks

 

So, I'm running Unity 5.6.2f and am definitely 100% of the time getting this crash to occur on iOS when calling Dispose() inside of a LoadFromCacheOrDownload call that is being cancelled.

 

I may have spoke prematurely, technically at least. After doing some more testing and removing Dispose() I find LoadFromCacheOrDownload still crashes on iOS if the cancelled state occurs.

Code (CSharp):

1. while (!Caching.ready)
2. yield return null;
3.         // Load the AssetBundle file from Cache if it exists with the same version or download and store it in the cache
4.         using(WWW www = WWW.LoadFromCacheOrDownload (URL, ver))
5.         {
6.             float lastProgressMade=www.progress;
7.             float lastProgressTimeStamp=Time.time;
8.             Debug.Log("Loading from: " + URL);
9.             while( !www.isDone && !cancelled && !timedOut )
10.             {
11.                 if (Time.time > startTime+timeBeforeLoadDisplay && !ModelManager.instance.BundleDownloadPanel.activeSelf)
12.                 {
13.                     ModelManager.instance.BundleDownloadPanel.SetActive(true);
14.                 }
15.  
16.                 //timeout logic
17.                 if (www.progress != lastProgressMade)
18.                 {
19.                     lastProgressMade = www.progress;
20.                     lastProgressTimeStamp = Time.time;
21.                     #if DEBUG
22.                     Debug.Log ("Bundle Download progress: " + www.progress);
23.                     #endif
24.                     ModelManager.instance.BundleProgressBar.value = www.progress;
25.                 }
26.                 else
27.                 {
28.                     if (Time.time > lastProgressTimeStamp + timeOutTime)    
29.                         timedOut=true;
30.                 }
31.  
32.                 yield return null;
33.             }
34.  
35.             if (cancelled)
36.             {
37.                 ModelManager.instance.BundleDownloadPanel.SetActive(false);            
38.                 www.Dispose();
39.                 Debug.Log ("Cancelled");
40.                 yield return errorCancelled;
41.                 yield break;
42.             }
43.  
44.             if (timedOut)
45.             {
46.                 ModelManager.instance.BundleDownloadPanel.SetActive(false);            
47.                 www.Dispose();            
48.                 Debug.Log ("Timed out");
49.                 RecordAnal.RecordEvent(assetName + " bundle download timed out");
50.                 yield return errorTimedOut;
51.                 yield break;
52.             }
53.  
54.             yield return www;
55.             if (!string.IsNullOrEmpty(www.error))
56.                 //throw new Exception("WWW download had an error:" + www.error);
57.             {
58.                 Debug.LogError("WWW download had an error:" + www.error);
59.                 RecordAnal.RecordEvent(assetName + " bundle download had an error: " + www.error);
60.                 yield return null;
61.             }
62.             else
63.             {
64.                 if (assetName!="")
65.                 {
66.                     AssetBundle bundle = www.assetBundle;
67.                     //yield return bundle.mainAsset;
68.                     yield return bundle.LoadAsset(assetName);
69.                     // Unload the AssetBundles compressed contents to conserve memory
70.                     bundle.Unload(false);
71.                 }
72.  
73.     //            if (AssetName == "")
74.     //                Instantiate(bundle.mainAsset);
75.     //            else
76.     //                Instantiate(bundle.LoadAsset(AssetName));
77.  
78.             }
79.         } // memory is freed from the web stream (www.Dispose() gets called implicitly)
80.         ModelManager.instance.BundleDownloadPanel.SetActive(false);
81.     }