To: cygwin@cygwin.com
Subject: sh.exe hangs when invoked from make without a terminal
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Message-ID: <OFF6CD940C.DC215CF2-ON802573B8.005306DE-802573B8.0055EB45@accelrys.com>
From: Stephen Bennett <sbennett@accelrys.com>
Date: Fri, 21 Dec 2007 15:38:28 +0000
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test.pl:
----
$childpid=fork;
die "failed to fork" if (!defined $childpid);
if (! $childpid) {
    close STDIN;
    close STDOUT;
    close STDERR;
    exec "make -f test.mk &>test.out";
}
----
test.mk:
----
var=$(shell echo foobar | cat)
 
default:
        @echo "$(var)"
----

Running "make -f test.mk" from a terminal works as expected -- "foobar" is 
echoed. Running test.pl, however, causes the sh.exe process to hang 
apparently indefinitely -- the first time I observed this was in an 
overnight cronjob, and `sh -c "echo xml4csrc2_2_0 |tr 'a-z' 'A-Z'"` had 
been running for approximately 11 hours.

The trigger appears to be the combination of make, the pipeline appearing 
in the shell command, and not being attached to a terminal. If I remove 
any of these factors (by removing the '| cat', changing 'make -f test.mk' 
into 'sh -c "echo foo | cat"', or running "make -f test.mk" from a 
terminal), the problem does not manifest itself and everything behaves as 
expected. I've so far managed to reproduce the problem on three different 
machines with versions 3.1.17 and 3.2.25 of bash, and versions 1.5.24-2 
and 1.5.25-7 of the cygwin DLL.

Any suggestions?


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