Date: Sun, 10 Oct 1999 21:36:05 -0700 (PDT) From: Alfred Perlstein <bright@wintelcom.net> To: Zhihui Zhang <zzhang@cs.binghamton.edu> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: How to prevent a system call from restart? Message-ID: <Pine.BSF.4.05.9910102134440.8080-100000@fw.wintelcom.net> In-Reply-To: <Pine.GSO.3.96.991010150931.28616A-100000@sol.cs.binghamton.edu>
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On Sun, 10 Oct 1999, Zhihui Zhang wrote:
>
> I modify the day time client program from the Stevens' book and run it on
> both a Sun workstation and a FreeBSD machine. In the program, I use
> signal() and alarm() to set a 5 seconds timeout. The program works as
> expected on Sun (after I comment out the daytime line in the file
> /etc/inetd.conf) but not on the FreeBSD machine.
>
> Later I find out that the reason maybe the recvfrom() restarts
> *automatically* in FreeBSD. Why the default behaviour is different from
> SunOS? If I am correct about the reason, can anyone tell me how to prevent
> the recvfrom() from restart after receiving the SIGALRM signal?
>
> By the way, I also try the socket timeout option. It works immediately.
>
> Any help is appreciated.
from sigaction's manpage:
If a signal is caught during the system calls listed below, the call may
be forced to terminate with the error EINTR, the call may return with a
data transfer shorter than requested, or the call may be restarted.
Restart of pending calls is requested by setting the SA_RESTART bit in
sa_flags. The affected system calls include open(2), read(2), write(2),
sendto(2), recvfrom(2), sendmsg(2) and recvmsg(2) on a communications
channel or a slow device (such as a terminal, but not a regular file) and
during a wait(2) or ioctl(2). However, calls that have already committed
are not restarted, but instead return a partial success (for example, a
short read count).
you want to turn off SA_RESTART.
-Alfred Perlstein - [bright@rush.net|alfred@freebsd.org]
Wintelcom systems administrator and programmer
- http://www.wintelcom.net/ [bright@wintelcom.net]
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