Fix deadlock when tearing down runtime during debugging #4352
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When trying to exit with a hard exit (exit!), runtime teardown is performed by the shutdown hook thread added in Main.internalRun(), which is run on a different thread. This poses a problem when using ruby-debug, as it grabs a lock while processing debug events [1], and thus if you try to exit! while trying to process debug events (for instance if you're debugging interactively with pry and you want to exit), you'll get a deadlock looking something like this: ``` "Thread-1" - Thread t@11 java.lang.Thread.State: BLOCKED at org.jruby.debug.DebugEventHook.eventHandler(DebugEventHook.java:91) - waiting to lock <3b88136f> (a org.jruby.debug.DebugEventHook) owned by "main" t@1 at org.jruby.runtime.EventHook.event(EventHook.java:30) at org.jruby.Ruby.callEventHooks(Ruby.java:3179) at org.jruby.runtime.ThreadContext.trace(ThreadContext.java:652) (...) at org.jruby.RubyProc.call(RubyProc.java:249) at org.jruby.Ruby.tearDown(Ruby.java:3281) at org.jruby.Ruby.tearDown(Ruby.java:3254) at org.jruby.Main$1.run(Main.java:293) Locked ownable synchronizers: - None "main" - Thread t@1 java.lang.Thread.State: WAITING at java.lang.Object.wait(Native Method) - waiting on <5579bb86> (a org.jruby.Main$1) at java.lang.Thread.join(Thread.java:1249) at java.lang.Thread.join(Thread.java:1323) at java.lang.ApplicationShutdownHooks.runHooks(ApplicationShutdownHooks.java:106) at java.lang.ApplicationShutdownHooks$1.run(ApplicationShutdownHooks.java:46) at java.lang.Shutdown.runHooks(Shutdown.java:123) at java.lang.Shutdown.sequence(Shutdown.java:167) at java.lang.Shutdown.exit(Shutdown.java:212) - locked <39d0fc85> (a java.lang.Class) at java.lang.Runtime.exit(Runtime.java:109) at java.lang.System.exit(System.java:971) at org.jruby.RubyKernel.exit(RubyKernel.java:708) at org.jruby.RubyKernel.exit_bang(RubyKernel.java:683) (...) at org.jruby.debug.DebugEventHook.eventHandler(DebugEventHook.java:97) - locked <3b88136f> (a org.jruby.debug.DebugEventHook) at org.jruby.runtime.EventHook.event(EventHook.java:30) at org.jruby.Ruby.callEventHooks(Ruby.java:3179) at org.jruby.runtime.ThreadContext.trace(ThreadContext.java:652) (...) at org.jruby.Main.main(Main.java:204) ``` To fix this, we disable event hooks during teardown, so that code events during this period are not sent to the debugger. [1]: https://github.com/ruby-debug/ruby-debug/blob/master/src/org/jruby/debug/DebugEventHook.java#L91-L101
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Hey Ivo, any chance you could look at ruby-debug whether this could be avoided there? |
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Ah, not good indeed. I will try to find other way to tackle this issue, thanks for the heads up. |
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When trying to exit with a hard exit (exit!), runtime teardown is
performed by the shutdown hook thread added in Main.internalRun(), which
is run on a different thread.
This poses a problem when using ruby-debug, as it grabs a lock while
processing debug events 1, and thus if you try to exit! while trying to
process debug events (for instance if you're debugging interactively
with pry and you want to exit), you'll get a deadlock looking something
like this:
To fix this, we disable event hooks during teardown, so that code events
during this period are not sent to the debugger.