[sldev] lltexturefetch.cpp patch for http-texture and/or snowglobe

[Steve Bennetts]

So, adding that lock exposed a flaw in the logic resulting in a 
deadlock. Below is the fix for that. The problem was that 
LLTextureCache::update() was keeping the mutex protecting mReaders[] and 
mWriters[] locked while calling completed() in the responders, however 
readComplete() and writeComplete() (calls to which get triggered by the 
responders) do their own locking of the mutex, triggering the deadlock. 
There is no reason for the mutex to be locked while calling these 
completed() functions.

-Steve


Index: lltexturecache.cpp
===================================================================
--- lltexturecache.cpp    (revision 121571)
+++ lltexturecache.cpp    (revision 121572)
@@ -779,6 +779,9 @@
         }
     }
 
+    unlockWorkers();
+   
+    // call 'completed' with workers list unlocked (may call 
readComplete() or writeComplete()
     for (responder_list_t::iterator iter1 = completed_list.begin();
          iter1 != completed_list.end(); ++iter1)
     {
@@ -787,8 +790,6 @@
         responder->completed(success);
     }
    
-    unlockWorkers();
-   
     return res;
 }
 


Steve Bennetts wrote:
> We will be applying this patch next week, but if someone wants to play, 
> I just discovered this major bug in lltexturefetch.cpp:
>
> void LLTextureFetchWorker::callbackDecoded(bool success, LLImageRaw* 
> raw, LLImageRaw* aux)
> {
> +    LLMutexLock lock(&mWorkMutex);
>
>     ...
>
>
> The missing mutex lock here can cause all sorts of terrible artifacts. 
> Don't know if this will fix everything, but it definitely addresses at 
> least one of the crashes I have been seeing.
>
> -Steve
>
>
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