[GitHub] [flink] hwanju edited a comment on pull request #14499: [FLINK-15156] Warn user if System.exit() is called in user code

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hwanju edited a comment on pull request #14499:
URL: https://github.com/apache/flink/pull/14499#issuecomment-761572560


   > I believe sources are relatively important, in particular because some users have their own implementations there.
   > @hwanju do you want to address this in this PR, or in a follow up?
   
   This is nice catch! This should be addressed as part of this PR. When this patch was written, the old Flink version did invoke `run()` in `invoke()` in the same thread, but now with mailbox approach, it spawns a separate thread for run(). Yes, `FlinkSecurityManager` supports thread-inherited monitoring flag, so why this spawned thread wasn't protected? The reason is the thread local variables are inherited at the time of thread construction, not thread run, and the construction happens in `loadAndInstantiateInvokable` before `invoke`. By wrapping `loadAndInstantiateInvokable` with exit monitoring, I see it's protected as follows:
   
   ```
   org.apache.flink.runtime.UserSystemExitException: Flink user code attempted to exit JVM.
   	at org.apache.flink.runtime.security.FlinkSecurityManager.checkExit(FlinkSecurityManager.java:184)
   	at java.lang.Runtime.exit(Runtime.java:107)
   	at java.lang.System.exit(System.java:971)
   	at org.apache.flink.streaming.tests.FailureTestSource.run(FailureTestSource.java:65)
   	at org.apache.flink.streaming.api.operators.StreamSource.run(StreamSource.java:110)
   	at org.apache.flink.streaming.api.operators.StreamSource.run(StreamSource.java:66)
   	at org.apache.flink.streaming.runtime.tasks.SourceStreamTask$LegacySourceFunctionThread.run(SourceStreamTask.java:245)
   ```
   
   Added unit test (reproduced without fix, and fixed after it).


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