Zeugswetter Andreas SB <[EMAIL PROTECTED]> writes:
>> HPUX has usleep, but the man page says
>>
>> The usleep() function is included for its historical usage. The
>> setitimer() function is preferred over this function.
> I doubt that setitimer has microsecond precision on HPUX.
Well, if you insist on beating this into the ground:
$ cat timetest.c
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int main(int argc, char** argv)
{
int i;
int delay;
delay = atoi(argv[1]);
for (i = 0; i < 1000; i++)
usleep(delay);
return 0;
}
$ gcc -O -Wall timetest.c
$ time ./a.out 1
real 0m20.02s
user 0m0.04s
sys 0m0.09s
$ time ./a.out 1000
real 0m20.04s
user 0m0.04s
sys 0m0.09s
$ time ./a.out 10000
real 0m20.01s
user 0m0.03s
sys 0m0.08s
$ time ./a.out 20000
real 0m30.03s
user 0m0.04s
sys 0m0.09s
$
$ cat timetest2.c
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <time.h>
#include <unistd.h>
typedef void (*pqsigfunc) (int);
pqsigfunc
pqsignal(int signo, pqsigfunc func)
{
struct sigaction act,
oact;
act.sa_handler = func;
sigemptyset(&act.sa_mask);
act.sa_flags = 0;
if (signo != SIGALRM)
act.sa_flags |= SA_RESTART;
if (sigaction(signo, &act, &oact) < 0)
return SIG_ERR;
return oact.sa_handler;
}
void
catch_alarm(int sig)
{
}
int main(int argc, char** argv)
{
int i;
struct itimerval iv;
int delay;
delay = atoi(argv[1]);
pqsignal(SIGALRM, catch_alarm);
for (i = 0; i < 1000; i++)
{
iv.it_value.tv_sec = 0;
iv.it_value.tv_usec = delay;
iv.it_interval.tv_sec = 0;
iv.it_interval.tv_usec = 0;
setitimer(ITIMER_REAL, &iv, NULL);
pause();
}
return 0;
}
$ gcc -O -Wall timetest2.c
$ time ./a.out 1
real 0m20.04s
user 0m0.01s
sys 0m0.05s
$ time ./a.out 1000
real 0m20.02s
user 0m0.01s
sys 0m0.06s
$ time ./a.out 10000
real 0m20.01s
user 0m0.01s
sys 0m0.05s
$ time ./a.out 20000
real 0m30.01s
user 0m0.01s
sys 0m0.06s
$
The usleep man page implies that usleep is actually implemented as a
setitimer call, which would explain the interchangeable results. In
any case, neither one is useful for timing sub-clock-tick intervals;
in fact they're worse than select().
Anyone else want to try these examples on other platforms?
regards, tom lane
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