Re: echo interrupted by SIGCHLD from a dying coprocess

[Tomáš Trnka]

Dne So 27. března 2010 03:50:41 Chet Ramey napsal(a):
> On 3/24/10 3:30 PM, Tomáš Trnka wrote:
> > Configuration Information [Automatically generated, do not change]:
> > Machine: x86_64
> > OS: linux-gnu
> > Compiler: gcc
> > Compilation CFLAGS:  -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64' -
> > DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='x86_64-unknown-linux-gnu' -
> > DCONF_VENDOR='unknown' -DLOCALEDIR='/home/trnka/opt/share/locale' -
> > DPACKAGE='bash' -DSHELL -DHAVE_CONFIG_H   -I.  -I. -I./include -I./lib  
> > -g - O2
> > uname output: Linux a324-2 2.6.24.2 #1 SMP Wed Feb 20 12:36:17 CET 2008
> > x86_64 GNU/Linux
> > Machine Type: x86_64-unknown-linux-gnu
> > 
> > Bash Version: 4.1
> > Patch Level: 2
> > Release Status: release
> > 
> > Description:
> > I've started using coprocesses heavily and I've found a nasty problem
> > related (but not limited) to them: After the coprocess finishes its job,
> > the resultant SIGCHLD is not properly blocked by bash signal processing
> > logic and interferes with script I/O. In my case, I've been using
> > something like:
> > 
> > read var1 var2 < <( a | long | pipeline | here)
> > echo "var1=$var1"
> > echo "var2=$var2"
> > 
> > Sometimes, the SIGCHLD arrived just when one of the echos were doing
> > output and the result was:
> > echo: write error: Interrupted system call
> > As this is a bit of a race, it occurs only when the stars are right, i.e.
> > during normal usage the probability of the SIGCHLD hitting exactly the
> > echo is quite low. However, as soon as anything causes the I/O to take
> > significantly longer, the bug appears. I've been hitting quite often
> > (30%?) when running the script over SSH.
> 
> I think there's an easier way to do this.  Try the attached patch and
> see what you get.
> 
> Chet
>
> *** ../bash-4.1-patched/sig.c   Fri Aug 14 16:31:52 2009
> --- sig.c       Fri Mar 26 22:34:11 2010
> ***************
> *** 655,660 ****
> --- 655,663 ----
>      act.sa_flags |= SA_INTERRUPT;     /* XXX */
>    else
>      act.sa_flags |= SA_RESTART;               /* XXX */
>+ #else
>+   if (sig == SIGCHLD)
>+     act.sa_flags |= SA_RESTART;
>  #endif
>    sigemptyset (&act.sa_mask);
>    sigemptyset (&oact.sa_mask);

Hello there,

could you please release this as an official Bash patch? It's been almost half 
a 
year and it seems not to cause any problems...
Best regards

2T

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