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From: Bart Schaefer <schaefer@brasslantern.com>
Message-id: <130425175341.ZM17766@torch.brasslantern.com>
Date: Thu, 25 Apr 2013 17:53:41 -0700
In-reply-to: <klc0n1$34u$1@ger.gmane.org>
Comments: In reply to "Yuri D'Elia" <wavexx@users.sourceforge.net>
 "Re: precmd: write error: interrupted" (Apr 25,  9:38pm)
References: <klbmnc$ieh$1@ger.gmane.org>
	<130425111646.ZM17258@torch.brasslantern.com>	<klc0n1$34u$1@ger.gmane.org>
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To: zsh-workers@zsh.org, "Yuri D'Elia" <wavexx@users.sourceforge.net>,
 zsh-users@zsh.org
Subject: Re: precmd: write error: interrupted
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(Redirecting this to -workers, so Yuri Cc'd in case he's only on -users)

On Apr 25,  9:38pm, Yuri D'Elia wrote:
}
} precmd() { { print x } 2>/dev/null }
} 
} still doesn't suppress the error.

Interesting!  Something is restoring the stderr descriptors before the
error message in bin_print is written.  Here is a bit of strace from
'zsh -f' with { print -n $'x\r' } 2>/devnull running in a loop on the
command line (not from a precmd):

open("/dev/null", O_WRONLY|O_CREAT|O_NOCTTY|O_TRUNC|O_LARGEFILE, 0666) = 3
dup2(3, 2)                              = 2
write(1, "x\r", 2)                      = ? ERESTARTSYS (To be restarted)
--- SIGWINCH (Window changed) @ 0 (0) ---
dup2(12, 2)                             = 2
dup2(11, 2)                             = 2
write(10, "\33[1m\33[7m%\33[27m\33[1m\33[0m                                     
                                           \r \r", 105) = 105
write(2, "print: write error: interrupt\n", 30) = 30

Those dup2 calls should happen only at the end of execcmd after bin_print
has already returned, but somehow they appear to be happening after the
signal handler is called but before the error message.

Attaching with a debugger blocks the interrupt so I haven't been able to
stack-trace the source of the dup2 calls.