Re: parallel autotest [2/3]: Implement 'testsuite --jobs'.

[Eric Blake]

Eric Blake <ebb9 <at> byu.net> writes:

> 
> > +if test $at_jobs -ne 1 &&
> > +     rm -f "$at_job_fifo" &&
> > +     ( mkfifo "$at_job_fifo" ) 2>/dev/null &&
> > +     exec AT_JOB_FIFO_FD<> "$at_job_fifo"
> 
> Is exec n<> portable?  Yes, POSIX specifies it, but I haven't seen it used
> anywhere else in autoconf.  I guess we commit it now, and if it is not
> portable, we wrap it inside an eval alongside the mkfifo check as a reason
> to skip the parallel testing.

Unfortunately, it is NOT portable.  According to POSIX open [1], under 
O_RDWR, "The result is undefined if this flag is applied to a FIFO."  On 
cygwin, FIFOs can only be read-only or write-only, there is no way to get a 
read-write FIFO, and using <> in the shell defaults to a read-only FIFO.

[1] http://www.opengroup.org/onlinepubs/009695399/functions/open.html

As a result, the parallel tests invariably fail:

./autotest.at:837: $CONFIG_SHELL ./micro-suite -j4
--- /dev/null   2006-11-30 17:00:00.000000000 -0700
+++ /home/eblake/autoconf/tests/testsuite.dir/at-groups/133/stderr      2008-10-
02 09:42:30.020100900 -0600
@@ -0,0 +1,8 @@
+./micro-suite: line 1703: read: read error: 0: Communication error on send
+./micro-suite: line 1716: read: read error: 0: Communication error on send
+./micro-suite: line 1716: read: read error: 0: Communication error on send
+./micro-suite: line 1716: read: read error: 0: Communication error on send
+./micro-suite: line 1699: echo: write error: Communication error on send
+./micro-suite: line 1699: echo: write error: Communication error on send
+./micro-suite: line 1699: echo: write error: Communication error on send
+./micro-suite: line 1699: echo: write error: Communication error on send
stdout:

Can we work on refactoring this into two fd's both visiting the same FIFO, one 
for writing tokens, and the other for reading tokens, rather than using <>?

-- 
Eric Blake