[D-runtime] A mechanism to kill threads

[Sean Kelly]

Why does this need to be built into core.thread?  Is there some reason you can't implement a kill routine in your app?

On May 16, 2012, at 2:29 PM, Alex Rønne Petersen wrote:

> The only reason I can think of is exactly what you mentioned, but this
> is a non-issue because you *really* *should* *not* kill non-daemon
> threads, and daemon threads should be designed to handle 'abnormal'
> termination gracefully.
> 
> That said, I think it's okay to kill a thread which is just waiting
> for work, sleeping, or whatever. As long as it isn't holding onto a
> lock (or similar), you should be safe. Holding onto a resource like a
> lock could easily lead to a deadlock because the lock is never
> released when you kill the thread.
> 
> I think the TL;DR of all this is that you should really only kill
> threads if either a) you know they can tolerate it (daemon threads) or
> b) you know specifically what the thread is doing and that it's safe
> to interrupt that work and never resume it (speaking of which, killing
> a thread isn't really any different from suspending it and just never
> resuming it).
> 
> Regards,
> Alex
> 
> On Wed, May 16, 2012 at 11:19 PM, David Simcha <dsimcha at gmail.com> wrote:
>> For the sake of argument, what are the most non-obvious reasons why killing
>> threads is bad?  The ones I can think of are because the thread may be in
>> the middle of doing something important and bad things will happen if it's
>> interrupted and because the thread might hold resources that will never get
>> freed if it's killed before it gets to free them.
>> 
>> I was thinking at one point that I wanted a kill() primitive when I was
>> designing std.parallelism, but I don't remember why I wanted it and
>> obviously I've managed to do without it.  Is it ok to kill threads if
>> they're not doing useful work at the time and they're not holding onto any
>> resources that will never get freed if you kill them?
>> 
>> 
>> On Wed, May 16, 2012 at 5:04 PM, Jonathan M Davis <jmdavisProg at gmx.com>
>> wrote:
>>> 
>>> On Wednesday, May 16, 2012 20:57:15 Alex Rønne Petersen wrote:
>>>> Of course it's unsafe, but no less than arbitrarily suspending a
>>>> thread. Once you've suspended a thread, you may as well kill it.
>>>> You've effectively halted it anyway. We have lots of unsafe primitives
>>>> in core.thread already (and my critical regions and cooperative
>>>> suspension patches add even more!).
>>>> 
>>>> Is there anything speaking against adding this to core.thread with a
>>>> big fat "THIS IS UNSAFE" warning?
>>> 
>>> Well, I wasn't saying that it's necessarily the case that we shouldn't add
>>> it.
>>> I was pointing out that it's a very unsafe thing to do and rarely needed
>>> such
>>> that it's not exactly surprising that it hasn't been added previously. If
>>> there's a real use case for it, it makes sense to add it given that it
>>> _is_
>>> something that's platform dependent, and part of the whole point of Thread
>>> is
>>> to provide a platform-independent API for handling threads. It probably
>>> _should_ have a big fat warning on it though, given that not all
>>> developers
>>> seem to get how insanely bad it is to kill a thread (at least, that seems
>>> to
>>> be the case given some thread-related questions I've seen in the past).
>>> 
>>> - Jonathan M Davis
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>> 
>> 
>> 
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