TimerTask is starting a non-daemon thread

[fzakaria]

I have a small reproduction example:

  def test_timer_task
    task = Concurrent::TimerTask.new(execution_interval: 1) do
      puts "Here"
    end
    task.execute
  end

The threads started by TimerTask should be daemons however the JVM does not shutdown.
There seems to be some other concurrent-ruby thread which is not a daemon

The problem is that at the end of the test, the JVM remains active and does not shutdown.

(The following is from jstack)

"pool-6-thread-1" #61 prio=5 os_prio=31 tid=0x00007fe599823800 nid=0xb103 in Object.wait() [0x0000700013a56000]
   java.lang.Thread.State: TIMED_WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        at java.lang.Object.wait(Object.java:460)
        at org.jruby.RubyThread$SleepTask.run(RubyThread.java:1410)
        - locked <0x000000076e124a08> (a com.concurrent_ruby.ext.SynchronizationLibrary$JRubyLockableObject)
        at org.jruby.RubyThread.executeBlockingTask(RubyThread.java:1463)
        at org.jruby.RubyThread.wait_timeout(RubyThread.java:1933)
        at com.concurrent_ruby.ext.SynchronizationLibrary$JRubyLockableObject.nsWait(SynchronizationLibrary.java:254)
        at com.concurrent_ruby.ext.SynchronizationLibrary$JRubyLockableObject$INVOKER$i$0$1$nsWait_DBG.call(SynchronizationLibrary$JRubyLockableObject$INVOKER$i$0$1$nsWait_DBG.gen)
        at org.jruby.internal.runtime.methods.JavaMethod$JavaMethodN.call(JavaMethod.java:796)
        at org.jruby.internal.runtime.methods.DynamicMethod.call(DynamicMethod.java:202)
        at org.jruby.runtime.callsite.CachingCallSite.call(CachingCallSite.java:153)
        at org.jruby.ir.interpreter.InterpreterEngine.processCall(InterpreterEngine.java:315)
        at org.jruby.ir.interpreter.InterpreterEngine.interpret(InterpreterEngine.java:159)
        at org.jruby.ir.interpreter.Interpreter.INTERPRET_BLOCK(Interpreter.java:127)
        at org.jruby.runtime.InterpretedIRBlockBody.yieldDirect(InterpretedIRBlockBody.java:109)
        at org.jruby.runtime.IRBlockBody.yieldSpecific(IRBlockBody.java:80)
        at org.jruby.runtime.Block.yieldSpecific(Block.java:134)
        at org.jruby.RubyKernel.loop(RubyKernel.java:1316)
        at org.jruby.RubyKernel$INVOKER$s$0$0$loop_DBG.call(RubyKernel$INVOKER$s$0$0$loop_DBG.gen)
        at org.jruby.internal.runtime.methods.JavaMethod$JavaMethodZeroBlock.call(JavaMethod.java:536)
        at org.jruby.runtime.callsite.CachingCallSite.call(CachingCallSite.java:77)
        at org.jruby.runtime.callsite.CachingCallSite.callIter(CachingCallSite.java:84)
        at org.jruby.ir.instructions.CallBase.interpret(CallBase.java:429)
        at org.jruby.ir.interpreter.InterpreterEngine.processCall(InterpreterEngine.java:360)
        at org.jruby.ir.interpreter.InterpreterEngine.interpret(InterpreterEngine.java:159)
        at org.jruby.ir.interpreter.InterpreterEngine.interpret(InterpreterEngine.java:84)
        at org.jruby.internal.runtime.methods.InterpretedIRMethod.INTERPRET_METHOD(InterpretedIRMethod.java:182)
        at org.jruby.internal.runtime.methods.InterpretedIRMethod.call(InterpretedIRMethod.java:165)
        at org.jruby.runtime.callsite.CachingCallSite.call(CachingCallSite.java:163)
        at org.jruby.runtime.callsite.CachingCallSite.callIter(CachingCallSite.java:170)
        at org.jruby.ir.interpreter.InterpreterEngine.processCall(InterpreterEngine.java:336)
        at org.jruby.ir.interpreter.InterpreterEngine.interpret(InterpreterEngine.java:159)
        at org.jruby.ir.interpreter.Interpreter.INTERPRET_BLOCK(Interpreter.java:127)
        at org.jruby.runtime.InterpretedIRBlockBody.yieldDirect(InterpretedIRBlockBody.java:109)
        at org.jruby.runtime.BlockBody.yield(BlockBody.java:114)
        at org.jruby.runtime.Block.yield(Block.java:165)
        at com.concurrent_ruby.ext.SynchronizationLibrary$JRubyLockableObject.rubySynchronize(SynchronizationLibrary.java:232)
        - locked <0x000000076e124a08> (a com.concurrent_ruby.ext.SynchronizationLibrary$JRubyLockableObject)
        at com.concurrent_ruby.ext.SynchronizationLibrary$JRubyLockableObject$INVOKER$i$0$0$rubySynchronize_DBG.call(SynchronizationLibrary$JRubyLockableObject$INVOKER$i$0$0$rubySynchronize_DBG.gen)

* Operating system:               mac
* Ruby implementation:             jruby 9.1.17.0 (2.3.3)
* `concurrent-ruby` version:       1.1.5
* `concurrent-ruby-ext` installed: no
* `concurrent-ruby-edge` used:     no

[fzakaria]

I've created a minimal reproduction repository: https://github.com/fzakaria/concurrent-ruby-timer-task-failure

git clone git@github.com:fzakaria/concurrent-ruby-timer-task-failure.git
cd concurrent-ruby-timer-task-failure
bundle install
ruby test_timer_task.rb

Run options: --seed 4038

# Running:

.

Finished in 0.021096s, 47.4025 runs/s, 0.0000 assertions/s.

1 runs, 0 assertions, 0 failures, 0 errors, 0 skips
# NEVER EXITS

[kaikuchn]

Maybe this is related to #817?

[fzakaria]

Great find!
I'll submit a PR with the places he found.

[fzakaria]

PR submitted!