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expect - broken pipe


I'm trying to run the GCC DejaGNU testsuite on 32-bit Cygwin. It randomly
fails with the message:

"parent: sync byte write: broken pipe"

This occurs frequently if the testsuite is run in parallel (i.e. make -j4),
but occasionally when not in parallel too.

It seems this error message is generated by the 'expect' program,
specifically from exp_command.c. This does roughly the following:

pid = fork();
if (pid) { /* parent */

    /* wait for slave to initialize */
    while (((rc = read(sync_fds[0],&sync_byte,1)) < 0) && (errno == EINTR))
        /* empty */;
   /* tell slave to go on */
    wc = write(sync2_fds[1]," ",1);
    if (wc == -1) {
       expErrorLog("parent: sync byte write: %s\r\n",Tcl_ErrnoMsg(errno));

So, the write to the pipe is failing randomly with errno==EPIPE. Any idea
why this might be?

What is strange, is if I remove the call to close(sync2_fds[0]), then the
write never fails. Closing the unused end of the pipe seems fairly standard
behaviour as that is what is given as an example in the pipe() man page.


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