linuxMachine:/tmp # uname -a
Linux linuxMachine 2.4.21-309.PTF.97199.1-smp #1 SMP Mon Jul 24 12:20:00 UTC 2006 i686 unknown
linuxMachine:/tmp # cat testSelectCall.c
#include "stdio.h"
#include "sys/time.h"
#include "sys/types.h"
#include "unistd.h"
int
main(void) {
fd_set rfds;
struct timeval tv;
int retval;
FD_ZERO(&rfds);
FD_SET(0, &rfds);
tv.tv_sec = 5;
tv.tv_usec = 0;
retval = select(1, &rfds, NULL, NULL, &tv);
/* Here is the tricky part! */
printf("tv.tv_sec=%i\n",tv.tv_sec);
printf("tv.tv_usec=%i\n",tv.tv_usec);
if (retval)
printf("Data is available now.\n");
else
printf("No data within five seconds.\n");
return 0;
}
linuxMachine:/tmp # !gcc
gcc testSelectCall.c
linuxMachine:/tmp # !time
time ./a.out
tv.tv_sec=0
tv.tv_usec=0
No data within five seconds.
real 0m5.000s
user 0m0.000s
sys 0m0.000s
linuxMachine:/tmp #
On a solaris box
solarisBox>uname -a
SunOS solarisBox 5.10 Generic_118835-02 sun4u sparc SUNW,Sun-Blade-100
solarisBox>gcc testSelectCall.c
solarisBox>!time
time ./a.out
tv.tv_sec=5
tv.tv_usec=0
No data within five seconds.
real 0m5.025s
user 0m0.003s
sys 0m0.010s
solarisBox>
Man Page has the following description
man 2 select
Some code calls select with all three sets empty, n zero, and a non-null
timeout as a fairly portable way to sleep with subsecond precision.
On Linux, the function select modifies timeout to reflect the amount of
time not slept; most other implementations do not do this. This causes
problems both when Linux code which reads timeout is ported to other
operating systems, and when code is ported to Linux that reuses a struct
timeval for multiple selects in a loop without reinitializing it. Con�
sider timeout to be undefined after select returns.
