nearly-tickless-tinc

[Guus Sliepen]

On Sun, May 29, 2011 at 10:17:03PM +0200, Loïc Grenié wrote:

> > but to prevent race conditions, only pselect() should change the
> > signal mask in the main loop.
> 
>      I might be wrong but I think there is no race condition in my code.
>   However I can eliminate all the problems if you tell me that tincd
>   does not block/unblock SIGHUP and SIGALARM while running
>   (block_mask can be initialized before the main loop, signals blocked
>   there and never unblocked). In that case the main loop is mostly
>   unchanged (except for computing "next_event") and we can
>   emulate pselect() when it does not exist (or is racy) by a
>   standard select() with a 1s timeout (without blocking signals
>   obviously).

Tinc never changes the signal mask. The only thing it does is install signal
handlers. So you can read the signal mask once before main_loop(), add SIGUP
and SIGALARM, and use that for pselect().

>      The "selfpipe" trick is another option obviously if you prefer. It is
>   not very elegant but has no real downside (I don't know whether
>   there are pipes under Windows, but since there are no signals
>   anyway...).

Windows has pipes. But again, I think it is less work and code to use
pselect(). You might want to check whether it is properly supported on the BSD
variants (including MacOS/X) though.

-- 
Met vriendelijke groet / with kind regards,
     Guus Sliepen <guus at tinc-vpn.org>
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