Launcher hard crashes when using a custom Java installation with modded instances

Hello,

Over on the Fabric (Users of optifine and forge seem to experience the same issue as well) discord we have been getting a number of reports of the latest vanilla launcher crashing with fabric.

This seems to be the case on windows and mac when using a custom java version with modded instances such as fabric. As far as im aware no one has been able to reproduce this with vanilla.

In my testing I am able to stall the launcher on windows, and hard crash it on MacOS. In all cases there doesnt appear to be anything useful in the log files. (MacOS provided a thread dump) You can see the issue that was raised on our issue tracker here: https://github.com/FabricMC/fabric-loader/issues/399

I have attached logs from our users who are based on windows, and included a thread dump that MacOS provided. 

 

Please let me know if you require anymore information, I will do my best to help resolve this issue.

 

Many Thanks