Re: A signal fairy tale

From: Daniel R. Kegel (
Date: Wed Jun 27 2001 - 21:57:47 EST

From: Christopher Smith <>
>> [ sigopen() proposal ]
>... From a programming standpoint, this
>looks like a really nice approach. I must say I prefer this approach to the
>various "event" strategies I've seen to date, as it fixes the primary
>problem with signals, while still allowing us to hook in to all the
>standard POSIX API's that already use signals.

Thanks. I'm sure people already thought of this long ago, it's basically just
the usual "In Unix, everything's a file". Until you ran into that
problem where the jvm was stealing your signals, though, I hadn't seen
a situation where having signals behave like files would be important.

>It'd be nice if I could pass
>in a 0 for signum and have the kernel select from unused signals (problem
>being that "unused" is not necessarily easy to define), althouh I guess an
>inefficient version of this could be handled in userland.

There is a (non-threadsafe) convention that Jamie Lokier pointed out
for finding an unused thread. If we allowed sigopen(-1) to allocate
a new signal for you, it'd probably just use the same scheme...

>I presume the fd could be shared between threads and otherwise behave like
>a normal fd, which would be sooooper nice.


>I guess the main thing I'm thinking is this could require some significant
>changes to the way the kernel behaves. Still, it's worth taking a "try it
>and see approach". If anyone else thinks this is a good idea I may hack
>together a sample patch and give it a whirl.

What's the biggest change you see? From my (two-martini-lunch-tainted)
viewpoint, it's just another kind of signal masking, sorta...

>Thanks again good fairy Dan/Eunice. ;-)

You're welcome (and I'll tell Eunice you liked her idea!).

- Dan

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