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RE: PATCH: ptyread eating CPU on Cygwin
- X-seq: zsh-workers 13030
- From: "Andrej Borsenkow" <Andrej.Borsenkow@xxxxxxxxxxxxxx>
- To: "Zsh hackers list" <zsh-workers@xxxxxxxxxxxxxx>
- Subject: RE: PATCH: ptyread eating CPU on Cygwin
- Date: Wed, 18 Oct 2000 20:44:44 +0400
- Importance: Normal
- In-reply-to: <1001018155547.ZM4463@xxxxxxxxxxxxxxxxxxxxxxx>
- Mailing-list: contact zsh-workers-help@xxxxxxxxxxxxxx; run by ezmlm
>
> I'm not Sven, but HAVE_SELECT does not imply having FD_ZERO or an fd_set
> typedef.
>
> On the other hand, I've just noticed that other code assumes in several
> places that it does imply those things, so it's probably OK.
>
Yes, it was just copy'n'paste.
> However, using a NULL timeout structure in the select() call has turned a
> non-blocking read into a fully blocking one. If you're going to do that,
> you might as well throw out the select() call and just set the descriptor
> back to blocking state before calling read(). I suspect there's a good
> reason it was a non-blocking read in the first place, though.
>
Erm. You are right, of course.
Non-blocking read made sense in initial implemetation, because it was the
condition to exit read loop (without pattern matching) - 9390:
+ do {
+ while ((ret = read(cmd->fd, buf + used, 1)) == 1) {
+ if (++used == blen) {
+ buf = hrealloc(buf, blen, blen << 1);
+ blen <<= 1;
+ }
+ }
+ buf[used] = '\0';
+ } while (prog && !pattry(prog, buf));
Currently zsh tries to always read the whole input (until EOF) Actually, in
pattern-matching mode it even completely ignores EOF. That makes absolutely no
functional difference between blocking and non-blocking mode but makes
performance in non-blocking mode terrible.
As it stands now, we really can just use blocking read.
-andrej
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