[racket] SIgnal-catching in Racket

From: Tony Garnock-Jones (tonyg at ccs.neu.edu)
Date: Sun Dec 21 15:53:34 EST 2014

Thanks Matthew and Robby! I'll give the self-pipe trick a try.


On 12/21/2014 09:01 AM, Matthew Flatt wrote:
> You're right that can't post to a Racket semaphore in a signal handler.
> The way to allocate a global and make it available to Racket code is to
> create a new kind of event; the 2006 post is still accurate. In
> particular, the new event's polling function (which is called by the
> scheduler) can check the global. Calling scheme_signal_received() from
> a signal handler ensures that the event's polling function is called
> after the global is changed.
> A self-pipe is also a fine approach, since the event wrapper for a pipe
> is already available via scheme_make_fd_input_port().
> At Sat, 20 Dec 2014 14:05:32 -0500, Tony Garnock-Jones wrote:
>> Hi all,
>> If I wanted to catch a Unix signal (say, SIGUSR1) within my Racket
>> program, how should I go about it?
>> My current best guess is:
>>  - load a C extension, which
>>  - creates a semaphore and
>>  - hooks the signal with a handler (MZ_SIGSET looks relevant), which
>>  - posts to the semaphore when the signal arrives.
>> However this seems like a recipe for problems. Is it even permitted to
>> post to a semaphore from a signal handler? Will the runtime be upset
>> about unscheduled intrusions into its demesne? Is it possible for a C
>> extension to allocate a global value like a semaphore and make it
>> available to Racket code?
>> Is there a better way?
>>  - Perhaps a self-pipe would be better than a semaphore?
>>  - A thread from 2006 [1] points at scheme_signal_received() but
>>    I don't understand why creating an event type is the right thing
>>    to do.
>> Tony
>> [1] http://lists.racket-lang.org/users/archive/2006-July/013999.html
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