Re: exec fd>>(list) freezes

[Peter Stephenson <pws@csr.com>]

Clint Adams wrote:
> In the past, "exec 8>>(grep a)" used to work; now it doesn't return.  Is
> this broken or am I confused?
...
> > Specifically, it worked in 4.0.9 and prior versions, but chokes on 4.1.1
> > and later.
> 
> Is this because of 18492?

Yes, it's now waiting for the grep process to finish.  This is
obviously inappropriate if the fd is being opened for the shell's
own future use.

A test for this might be sensible, but in this case the race which was
fixed by 18492 is intrinsic.  You don't even have a PID to wait for.
(If you had wanted one, you would have used a coprocess.)

Index: Src/exec.c
===================================================================
RCS file: /cvsroot/zsh/zsh/Src/exec.c,v
retrieving revision 1.76
diff -u -r1.76 exec.c
--- Src/exec.c	21 Oct 2004 00:33:50 -0000	1.76
+++ Src/exec.c	29 Oct 2004 10:01:39 -0000
@@ -2205,7 +2205,7 @@
 
     /* Do process substitutions */
     if (redir)
-	spawnpipes(redir);
+	spawnpipes(redir, nullexec);
 
     /* Do io redirections */
     while (redir && nonempty(redir)) {
@@ -3113,11 +3113,17 @@
 #endif   /* HAVE_FIFOS and PATH_DEV_FD not defined */
 }
 
-/* > >(...) or < <(...) (does not use named pipes) */
+/*
+ * > >(...) or < <(...) (does not use named pipes)
+ *
+ * If the second argument is 1, this is part of
+ * an "exec < <(...)" or "exec > >(...)" and we shouldn't
+ * wait for the job to finish before continuing.
+ */
 
 /**/
 static int
-getpipe(char *cmd)
+getpipe(char *cmd, int nullexec)
 {
     Eprog prog;
     int pipes[2], out = *cmd == Inang;
@@ -3133,7 +3139,8 @@
 	    zclose(pipes[!out]);
 	    return -1;
 	}
-	addproc(pid, NULL, 1, &bgtime);
+	if (!nullexec)
+	    addproc(pid, NULL, 1, &bgtime);
 	return pipes[!out];
     }
     entersubsh(Z_ASYNC, 1, 0, 0);
@@ -3157,11 +3164,17 @@
     pp[1] = movefd(pp[1]);
 }
 
-/* Do process substitution with redirection */
+/*
+ * Do process substitution with redirection
+ *
+ * If the second argument is 1, this is part of
+ * an "exec < <(...)" or "exec > >(...)" and we shouldn't
+ * wait for the job to finish before continuing.
+ */
 
 /**/
 static void
-spawnpipes(LinkList l)
+spawnpipes(LinkList l, int nullexec)
 {
     LinkNode n;
     Redir f;
@@ -3172,7 +3185,7 @@
 	f = (Redir) getdata(n);
 	if (f->type == REDIR_OUTPIPE || f->type == REDIR_INPIPE) {
 	    str = f->name;
-	    f->fd2 = getpipe(str);
+	    f->fd2 = getpipe(str, nullexec);
 	}
     }
 }

-- 
Peter Stephenson <pws@csr.com>                  Software Engineer
CSR Ltd., Science Park, Milton Road,
Cambridge, CB4 0WH, UK                          Tel: +44 (0)1223 692070


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