Parallel Access from Java Application causes SegFault in Lace

[kfriedberger]

Our Java application crashes deterministically when using one central JSylvan instance from multiple threads.

Reported SegFault:

# A fatal error has been detected by the Java Runtime Environment:
#    SIGSEGV (0xb) at pc=0x00007fe4839db5b0, pid=5258, tid=5279
# JRE version: OpenJDK Runtime Environment (11.0.9.1+1) (build 11.0.9.1+1-Ubuntu-0ubuntu1.18.04)
# Java VM: OpenJDK 64-Bit Server VM (11.0.9.1+1-Ubuntu-0ubuntu1.18.04,
#          mixed mode, sharing, tiered, compressed oops, g1 gc, linux-amd64)
# Problematic frame:
#    C  [libsylvan.so+0x395b0]  lace_get_head+0x0
# Core dump will be written....

Stacktrace when crashing:

Native frames: (J=compiled Java code, A=aot compiled Java code, j=interpreted, Vv=VM code, C=native code)
C  [libsylvan.so+0x395b0]  lace_get_head+0x0

Java frames: (J=compiled Java code, j=interpreted, Vv=VM code)
j  jsylvan.JSylvan.makeOr(JJ)J+0
j  parallel_nqueens.SylvanBDDRegionManager.makeOr(Lparallel_nqueens/SylvanBDDRegion;
      Lparallel_nqueens/SylvanBDDRegion;)Lparallel_nqueens/SylvanBDDRegion;+11
j  parallel_nqueens.NQueensMain.build()V+120
...

We provide a small example project here: parallelNqueens.zip
This example project tries to solve two instances of N-queens in parallel and
crashes with with SegFault instantly when JSylvan internally calles lace_get_head.
The problem happens deterministically on several Ubuntu-based machines under OpenJDK 11 and 15.