accessing zpty after child has finished (Mac OS X)

["Jun T." <takimoto-j@xxxxxxxxxxxxxxxxx>]

On Mac OS X, 'make check' succeeds normally, but zpty still has
some problems:

mac$ zpty x date
(date finishes immediately)
mac$ zpty -r x      # (1): no output
mac$ zpty
(20359) x: date     # should be (finished)
mac$ zpty -w x foo
(2): zsh goes into an infinite loop (100% cpu usage).

Suppose the child on the slave side of the pty has already finished,
and we try to read from the master by 'ret = read(master, buf, 1)'.
On Linux, what we get is either
  the data written to the slave but not yet read from the master,
  or ret = -1 (with errno set to EIO) if no such data remains.

On Mac OS X, the data not yet read by the master is lost,
and read() always returns 0 (not -1). 

The infinite loop (2) is in ptywritestr(); the for loop starting at
line 676 of zpty.c never breaks and loops forever, because checkptycmd()
(called at line 689) doesn't set cmd->fin. The following patch solves
this problem, and I hope it does no harm on other OS.

I feel the data loss (1) is OK at least for now.
The only way I can think of to avoid the data loss is to open the
slave in the parent and keep the file descriptor open in the parent.
But I believe it causes trouble on other OS.


diff --git a/Src/Modules/zpty.c b/Src/Modules/zpty.c
index fca0cc1..b0c339b 100644
--- a/Src/Modules/zpty.c
+++ b/Src/Modules/zpty.c
@@ -510,7 +510,7 @@ checkptycmd(Ptycmd cmd)
 
     if (cmd->read != -1 || cmd->fin)
 	return;
-    if ((r = read(cmd->fd, &c, 1)) < 0) {
+    if ((r = read(cmd->fd, &c, 1)) <= 0) {
 	if (kill(cmd->pid, 0) < 0) {
 	    cmd->fin = 1;
 	    zclose(cmd->fd);