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bug#37892: 27.0.50; Crash when signaling a thread
From: |
Michał Krzywkowski |
Subject: |
bug#37892: 27.0.50; Crash when signaling a thread |
Date: |
Sun, 27 Oct 2019 20:26:43 +0100 |
User-agent: |
mu4e 1.0; emacs 26.3.50 |
>>>>> "Eli" == Eli Zaretskii <eliz@gnu.org> writes:
Eli> But thread-signal is not for causing an error in a thread, it is for
Eli> unblocking a thread that waits on a mutex or a condvar. So why would
Eli> you use it when the thread is not blocked?
>>
>> Then I think documentation for that function should be changed to
>> explicitly say that the signal will *only* be delivered if the target
>> thread is in a "blocked call to ‘mutex-lock’, ‘condition-wait’, or
>> ‘thread-join’".
>>
>> Currently, the docstring of thread-signal just says that the function
>> will interrupt threads which are blocked, but does not actually say that
>> the signal will be delivered only in those cases. In fact, it says that
>> it works like signal, so I don't think it's unreasonable to assume that
>> it will just interrupt a thread whatever it's doing.
Eli> The function does work like a signal, but Emacs cannot be interrupted
Eli> while it waits for input. In all other cases your signal will be
Eli> delivered, and if unhandled, it will terminate the thread.
Eli> If we decide that thread-signal will have no effect while a thread
Eli> waits for input, then we will document that, of course. My question
Eli> was meant to understand your intent for signaling a thread at
Eli> arbitrary time, because the effect of that is unpredictable, even if
Eli> the crash didn't happen. I wanted to understand your thinking and
Eli> rationale, so as to have a better basis for the decision of how to fix
Eli> this problem.
Eli> So could you please elaborate on your rationale?
Actually there is no deeper reason behind it. I was just testing
threads in Emacs, seeing how things behave. I certainly would think
twice before writing code that interrupts a thread at an arbitrary point
in a real program.
When it comes to sit-for, I use it sometimes. Is there a reason not to
use it in threads?
In any case, I'm not encouraging anyone to program like that, I'm just
reporting a crash...
--
Michał Krzywkowski
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