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PhysX Crash During Destructible Mesh Creation

Hey guys,

Currently working on a project that involves building a lot of structures from hierarchical instanced static mesh components. We want these buildings to be destructible, so I've attached a component to the player character that, on tick, does an OverlapMultiByObjectType, gathers all the HISMCs in a radius around them, and replaces them with destructible mesh components.

After a certain number of conversions, the engine crashes. The number of conversions required varies based on settings (see below callstack for details).

The engine is crashing with this callstack:

 MachineId:2A2D385F4FB910D788020B9754E0EE1F
 EpicAccountId:72c1df1e45e54b6eb8d495162d6ae7d2
 
 Access violation - code c0000005 (first/second chance not available)
 
 ""
 
 APEX_DestructiblePROFILE_x64
 APEX_DestructiblePROFILE_x64
 APEX_DestructiblePROFILE_x64
 APEXFrameworkPROFILE_x64
 UE4Editor_Engine!TGraphTask<FPhysXTask>::ExecuteTask() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.10\engine\source\runtime\core\public\async\taskgraphinterfaces.h:779]
 UE4Editor_Core!FTaskThread::ProcessTasks() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.10\engine\source\runtime\core\private\async\taskgraph.cpp:539]
 UE4Editor_Core!FTaskThread::ProcessTasksUntilQuit() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.10\engine\source\runtime\core\private\async\taskgraph.cpp:340]
 UE4Editor_Core!FTaskThread::Run() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.10\engine\source\runtime\core\private\async\taskgraph.cpp:690]
 UE4Editor_Core!FRunnableThreadWin::Run() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.10\engine\source\runtime\core\private\windows\windowsrunnablethread.cpp:74]
 

I'm having serious trouble tracking this one down, and it's getting very frustrating. I have discovered two things:

1) Disabling "Form Extended Structures" on the destructible mesh significantly reduces the frequency of crashes (with it enabled, it crashes within the first 5-10 HISMC conversions. With it disabled, it can take from 13000 - 20000 conversions to do it). Note that having "Form Extended Structures" enabled also significantly reduces the project's performance/FPS, so perhaps physics processing time has a connection.

2) Enabling the async scene slightly reduces crash frequency (instead of 5-10 conversions, about 150 - 200).

3) Commenting out the destructible mesh spawning code, but leaving the HISMC removal code in, causes the crash to stop occuring. The other way around, however, does not. So it's connected to the destructible mesh spawning, not the HISMC removal.

I could really use some help on this. I can't have a crash like this lingering around in my project, and it's starting to feel impossible to debug on my own. Spent about 8-10 hours on it so far, fiddling with everything I could think of.

Thanks in advance!

Product Version: UE 4.10
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asked Jan 29 '16 at 11:01 PM in Bug Reports

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Beowulfe
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Hi Beowulfe,

Thanks for the details! This is a known crash that we have reported as UE-22078. It appears to be a PhysX crash when spawning Instanced Static Meshes at runtime. A fix has been created in our internal dev branches but it's not ready to integrate into the main branch quite yet. The developers are still hoping to get it fixed for 4.11. I'll update the post with your notes and let you know if I see any update on it. Thanks again!

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answered Jan 31 '16 at 05:39 PM

avatar image Beowulfe Feb 01 '16 at 03:48 PM

Great, thanks, keep me updated. Really hoping this makes it into 4.11, as it's a key component to our project.

Just to double check one thing - You mentioned it was a crash caused by spawning ISMs at runtime. As far as I can tell, with my crash, I can spawn and remove any number of ISMs without any issues. It's when I start spawning destructible mesh components in their place that the issue occurs.

I can see that still being related, but I wanted to double check there wasn't a second underlying issue at play.

avatar image Ben Halliday STAFF Feb 01 '16 at 04:31 PM

The devs believe it's a crash in destruction, something about a null entry in a deleted pair that isn't supposed to be null, so it may have more to do with replacing the ISMs with Destructible Meshes than simply spawning ISMs or Destructibles. Regardless, it's going to be difficult to be sure until this fix is integrated. If you're building from source, I can find the GitHub commit once it's released so you can try it, otherwise I'll figure out which Preview build it would make it to and let you know.

avatar image Beowulfe Feb 01 '16 at 04:50 PM

I'm not currently building from source, but I do have the GitHub engine files downloaded, so I can give it a shot once the commit goes live. If you get a chance to pass me the commit info once it up, that'd be great. I'll keep my eye on the 4.11 preview changes as well. Thanks. :)

avatar image RayJohannessen Apr 01 '16 at 08:31 PM

Hey, curious if this has this been resolved in the 4.11 patch...

avatar image Sean L ♦♦ STAFF Apr 06 '16 at 06:50 PM

Hello,

This issue has been reported fixed in 4.11. If you are still seeing the issue occur in 4.11, please let us know.

Have a great day

avatar image RayJohannessen Apr 07 '16 at 04:48 PM

Awesome, thanks Sean!

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