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

[Sheet Spotter]

The patch that Steve Linden provided resolves the deadlock I detailed in the
comments of VWR-13437.

The patch releases a mutex earlier, prior to making one of the calls that
led to the deadlock. Releasing the mutex earlier eliminates that deadlock.

Previously the HTTP-Texture viewer would hang on me after only a few minutes
of moving my camera using Alt-Mouse. After manually applying the patch I
have been unable to hang the viewer.

Thank you Steve!


Sheet Spotter

-----Original Message-----
From: sldev-bounces at lists.secondlife.com
[mailto:sldev-bounces at lists.secondlife.com] On Behalf Of Steve Bennetts
Sent: May 26, 2009 11:54 AM
To: Second Life Developer Mailing List
Subject: Re: [sldev] lltexturefetch.cpp patch for http-texture
and/orsnowglobe

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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