Issue #14143 has been updated by enebo (Thomas Enebo).


I think clarification on what the semantics should be would be helpful.

Should **ANY** exception raised in a Thread be considered a reasonable way of ending a thread? Yes or No

Yes - You execute your program and it does not work right.  Wondering why after doing weird stuff like method ensure blocks to print out the backtrace (yes I did that at one time) you find: Thread.abort_on_exception = true.  Once enabling and re-running (assuming it is predictable) you realize you made a typo and a NoMethodError killed your thread.

No - When your program does not work right you see a stack trace on a thread which died from an exception raise.

In No, the semantics is there is no reasonable exception to be thrown which will not generate a backtrace, but compared to Yes we do not get hidden death.  Hidden death makes developers frustrated and until they discover abort_on_exception they wonder why this is like this. Even after they learn this they still wonder why this is like this... :)

Besides asking a thread to kill we could always add a special exception which allows a thread to go away silently.  I personally think that is too much though.


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Feature #14143: Thread.report_on_exception should be true by default
https://bugs.ruby-lang.org/issues/14143#change-68125

* Author: Eregon (Benoit Daloze)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
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Extracted from #6647 to focus on the default value now that the feature is implemented.

I strongly believe we should have Thread.report_on_exception = true by default.

It only adds some extra stderr output for apps which let threads die, which is very rarely intended.
If it is intended, then one can use Thread.current.report_on_exception = false
to clarify it's OK for that thread to die and the failure is handled by the app on Thread#join.

I enabled Thread.report_on_exception=true by default in ruby/spec, see https://github.com/ruby/spec/pull/517,
the only cases needing Thread.current.report_on_exception=false
are the specs testing report_on_exception itself and Thread#join/value/status/raise.

Enabling it for test-all shows a fair amount of extra output and failures, which I would bet some of them are bugs in the tests (I already found one, r60854 & r60870),
and other tests should simply more carefully test what they expect
(for instance assert_raise() inside the Thread just around the code raising an exception and join the Thread).

I am willing to help to reduce the extra output and failures in test-all,
but I would like a OK from Matz to try enabling Thread.report_on_exception by default.

Dear Matz, do you think it is reasonable to show exceptions killing threads on stderr by default,
instead of silently swallowing them until Thread#join ?
(if there is ever a Thread#join ..., often not or too late, when the rest of the application has crashed)



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