Fatal error in GC: SuspendThread failed due to race condition #303

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1. tobil4sk commented on Dec 23, 2025

   

   tobil4sk

   on Dec 23, 2025

   Last edited by tobil4sk

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   This original issue should have been fixed with 8.2.10 (or 7.6.24). I tested with boehmgc 8.2.10 (#307) and the error appears to have gone away:

   Fatal error in GC
   SuspendThread loop failed
   

   The relevant upstream patches are:

   • bdwgc/bdwgc@fbf46d9
   • bdwgc/bdwgc@c920365

   However, in this version there is still a race condition which can cause thread creation to hang:

   function main() {
       while (true) {
           final lock = new sys.thread.Lock();
           Sys.print("Creating thread\r");
           sys.thread.Thread.create(function() {
               Sys.print("               \r");
               Sys.print(Date.now().getSeconds() + "\r");
               lock.release();
           });
           lock.wait();
           neko.vm.Gc.run(true);
       }
   }

   In this snippet, it eventually gets stuck on the "Creating thread" message.

   Further information is found in bdwgc/bdwgc#710.
2. Simn

   closed this as completedin #322on Mar 17, 2026