On 2005-09-13, Jacek Pop?awski <[EMAIL PROTECTED]> wrote:
> Grant Edwards wrote:
>> You're right. I must have been remembering the behavior of a
>> network socket. Apparently, you're supposed to read a single
>> byte and then call select() again. That seems pretty lame.
>
> I created another thread with single read(), it works, as long
> as I have only one PIPE (i.e. stderr is redirected into
> stdout). I wonder is it Python limitation or systems one (I
> need portable solution)?
Not sure what you mean. Here is my test program that blocks on
the read(1024) call:
#!/usr/bin/python
import os,select
p = os.popen("while sleep 2; do date; done","r")
print p
while 1:
r,w,e = select.select([p],[],[],1)
if r:
d = r[0].read(1024)
print len(d),repr(d)
else:
print "timeout"
It also blocks if the call is changed to read(). This seems
pretty counter-intuitive, since that's not the way read()
usually works on pipes.
Here's the corresponding C program that works as I
expected (read(1024) returns available data):
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/select.h>
unsigned char buffer[1024];
int main(void)
{
fd_set readfds, writefds, exceptfds;
struct timeval tv;
FILE *fp;
int fd;
fp = popen("while sleep 2; do date; done","r");
if (!fp)
{
perror("popen");
exit(1);
}
fd = fileno(fp);
FD_ZERO(&readfds);
FD_ZERO(&writefds);
FD_ZERO(&exceptfds);
while (1)
{
int s;
FD_SET(fd,&readfds);
tv.tv_sec = 1;
tv.tv_usec = 0;
s = select(fd+1,&readfds,&writefds,&exceptfds,&tv);
if (s==0)
printf("timeout\n");
else if (s<0)
{
perror("select");
exit(2);
}
else
{
if FD_ISSET(fd,&readfds)
{
int n = read(fd,buffer,(sizeof buffer)-1);
buffer[n] = '\0';
printf("read %d: '%s'\n",n,buffer);
}
}
}
}
--
Grant Edwards grante Yow! Does that mean
at I'm not a well-adjusted
visi.com person??
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