kolling@magic.ARPA (05/11/85)
Does anyone have a fix for the problem described below? Please send mail
to me at (kolling@decwrl.arpa or {decvax, purdue, sun, ucbvax}!decwrl!kolling)
as I don't normally read this newsgroup. Thanks.
/* Test program to prove that select() doesn't work correctly under
Unipress Emacs subshells.
Kenneth Brooks
5/9/85
DEC Systems Research Center
Expected behavior:
1. It types
What is your name?
and expects input, on the same line.
2. You type something, let's say, "Fred", and press Return.
3. It replies
Hello, Fred, nice to meet you.
When run under a C-shell on a terminal, this is in fact what it does.
But when run under a C-shell running in a window of Unipress Emacs
(which uses pty's), it waits 15 seconds before typing the reply and
finishing.
Analysis and debugger results:
Before doing the read to get the input, I do a select() kernel call
with descriptor 0 masked on as an interesting source of input. Select
is called with a 15 second timeout. In the normal case on the
terminal, select returns as soon as I press Return, and it reports
input on descriptor 0. In the bad case, on the pty, select does not
return until the timeout is up, and when it does, it returns 0.
Nevertheless, after select times out, a read works just fine, and
returns all the characters I typed.
Conclusion: select SIMPLY IS NOT AWARE of input events on a pty, at
least not a pty used in the manner that Unipress Emacs uses them.
*/
#define INCL(set, item) (set |= (1 << item))
typedef char Linebuf[80];
Linebuf outbuf1 = "What is your name? ";
Linebuf outbuf2 = "Hello, ";
Linebuf outbuf3 = ", nice to meet you.\n";
Linebuf inbuf;
int z, namesize;
main()
{
z = write(1, outbuf1, 19);
namesize = myread(0, inbuf, 80);
z = write(1, outbuf2, 7);
z = write(1, inbuf, namesize-1);
z = write(1, outbuf3, 20);
close(1);
}
/* I don't directly use the kernel call read, I use myread, which
uses the select() feature. It seems silly here, but this program is
abstracted from a large system in which it was important. */
#include <sys/time.h>
struct timeval time;
int readFDs, writeFDs, exceptFDs, nfound;
int myread(fd, buffer, nbytes)
int fd;
char *buffer;
int nbytes;
{
readFDs = 0; writeFDs = 0; exceptFDs = 0;
INCL(readFDs, fd);
time.tv_usec = 0;
time.tv_sec = 15;
/* here's the part that malfunctions */
nfound = select(32, &readFDs, &writeFDs, &exceptFDs, &time);
/* this is, in fact, a read */
return syscall(3, fd, buffer, nbytes);
}