Make ffi calls interruptible

[k-bx]

GHC 7.8 brought interruptible FFI. This might be very useful sometimes, especially upon hanging request through FFI. Some more context on a reddit thread.

What do you think? Would that be a good thing to have? Should mysql support GHC >=7.8 or would adding such thing require doing ifdefs to support older GHCs as well? Thanks.

[qrilka]

If I understand it correctly custom SIGPIPE handler is needed - https://dev.mysql.com/doc/refman/5.7/en/c-api-threaded-clients.html

[3noch]

Don't safe FFI calls also allow interruption? I'm pretty sure that's already happening here.

[qrilka]

@3noch Austin Seipp talks about it explicitly in the post linked above

[3noch]

@qrilka I see. Right now I think the C code is just blocking RTS signals: https://github.com/paul-rouse/mysql/blob/master/cbits/mysql_signals.c#L28-L32

[qrilka]

@3noch but only SIGALRM and SIGVTALRM are blocked.
MySQL docs say:

To use your own SIGPIPE handler, first call mysql_library_init(),
then install your handler.

I have tried unblocking SIGPIPE before doing a test query but the signal doesn't get through.

@paul-rouse could we know your opinion on this issue?

[paul-rouse]

Sorry, I'm not ignoring this, but I have a work deadline - I'll give it proper thought soon!