Java exception escaping exiting a monitor that hasn't been entered

[nirvdrum]

I'm working on refreshing our tags for the MRI tests. While doing so, I ran into a situation where a Java exception is escaping into Ruby when exiting a Monitor incorrectly.

The following code should raise a ThreadError, but instead we're triggering a ShouldNotReachHere exception.

require 'monitor'

m = Monitor.new
m.exit

On MRI, we see the ThreadError we expect:

> ruby -v bad-monitor.rb
ruby 3.1.3p185 (2022-11-24 revision 1a6b16756e) [arm64-darwin22]
bad-monitor.rb:4:in `exit': current fiber not owner (ThreadError)
        from bad-monitor.rb:4:in `<main>'

On TruffleRuby we end up an escaped Java exception.

> jt ruby -v bad-monitor.rb
truffleruby 23.0.0-dev-671182fb*, like ruby 3.1.3, GraalVM CE JVM [aarch64-darwin]

truffleruby: an internal exception escaped out of the interpreter,
please report it to https://github.com/oracle/truffleruby/issues.

the lock was not held when calling unlockInternal() (com.oracle.truffle.api.CompilerDirectives.ShouldNotReachHere)
        from com.oracle.truffle.api.CompilerDirectives.shouldNotReachHere(CompilerDirectives.java:574)
        from com.oracle.truffle.api.CompilerDirectives.shouldNotReachHere(CompilerDirectives.java:520)
        from org.truffleruby.core.mutex.MutexOperations.unlockInternal(MutexOperations.java:112)
        from org.truffleruby.core.mutex.MutexOperations.unlock(MutexOperations.java:105)
        from org.truffleruby.core.monitor.TruffleMonitorNodes$MonitorExit.exit(TruffleMonitorNodes.java:83)
        from org.truffleruby.core.monitor.TruffleMonitorNodesFactory$MonitorExitFactory$MonitorExitNodeGen.executeAndSpecialize(TruffleMonitorNodesFactory.java:476)
        from org.truffleruby.core.monitor.TruffleMonitorNodesFactory$MonitorExitFactory$MonitorExitNodeGen.execute(TruffleMonitorNodesFactory.java:467)
        from org.truffleruby.language.control.SequenceNode.execute(SequenceNode.java:37)
        from org.truffleruby.language.RubyMethodRootNode.execute(RubyMethodRootNode.java:65)
/Users/nirvdrum/dev/workspaces/truffleruby-ws/graal/sdk/mxbuild/darwin-aarch64/GRAALVM_A33290E019_JAVA17/graalvm-a33290e019-java17-23.0.0-dev/Contents/Home/languages/ruby/lib/mri/monitor.rb:194:in `mon_exit'
        from bad-monitor.rb:4:in `<main>'

[andrykonchin]

Fixed in b6c6096