Re: [Caml-list] BUG in unix.ml (was: strange errors when linking lwt.unix)

[oliver <oliver@first.in-berlin.de>]

On Fri, Mar 15, 2013 at 03:05:51PM +0000, Jeremie Dimino wrote:
> On Fri, Mar 15, 2013 at 2:27 PM, oliver <oliver@first.in-berlin.de> wrote:
> > Just by your activation of signal function
> > - not blocking, but handling "Sys.Signal_handle" but with the unreliable signal semantics
> > this has cause the problems.
> >
> > signal(2) opened the pandoras box.
> 
> Actually OCaml is using sigaction(2).  It is only using signal(2) when
> sigaction is not available.
> 
> Actually there are two different things here:
> 
> - signal disposition: this is a process-wide settings for each signal
> describing how to react when it is received.  It can be changed with
> the [sigaction] system call (or the less portable [signal]).
> - signal mask: it is a per-thread set of signals that are blocked.  It
> can be changed with sigprocmask.
> 
> When a signal is received by a thread, if it is blocked it will be
> pending until it is unblocked.  When it is not blocked and the
> threaded is waiting on an interruptible system call and the
> disposition of the signal is a user-defined handler, the system call
> will fail with EINTR and the handler will be invoked.
> 
> So basically Sys.set_signal and Unix.sigprocmask are two different
> things.  You should block signals when you are running some code that
> you don't want to be interrupted:
> 
>     # #load "unix.cma";;
>     # Sys.set_signal Sys.sigusr1 (Sys.Signal_handle (fun _ ->
> print_endline "signal!"));;
>     - : unit = ()
>     # let old_mask = Unix.sigprocmask Unix.SIG_BLOCK [Sys.sigusr1];;
>     val old_mask : int list = []
>     # Unix.kill (Unix.getpid ()) Sys.sigusr1;;
>     - : unit = ()
>     # Unix.sigprocmask Unix.SIG_SETMASK old_mask;;
>     signal!
>     - : int list = [-12]
> 
> The man page describing all this is signal(7).
[...]

I don't know why you are telling me this.
i did not asked about it.

But if you wish to explain it to yourself, go on.


Ciao,
   Oliver