1、
SYNOPSIS
#include <sys/time.h>
int getitimer(int which, struct itimerval *curr_value);
int setitimer(int which, const struct itimerval *new_value,
struct itimerval *old_value);
DESCRIPTION
These system calls provide access to interval timers, that is, timers that initially expire
at some point in the future, and (optionally) at regular intervals after that. When a timer
expires, a signal is generated for the calling process, and the timer is reset to the speci‐
fied interval (if the interval is nonzero).
Three types of timers—specified via the which argument—are provided, each of which counts
against a different clock and generates a different signal on timer expiration:
ITIMER_REAL This timer counts down in real (i.e., wall clock) time. At each expiration, a
SIGALRM signal is generated.
ITIMER_VIRTUAL This timer counts down against the user-mode CPU time consumed by the process.
(The measurement includes CPU time consumed by all threads in the process.)
At each expiration, a SIGVTALRM signal is generated.
ITIMER_PROF This timer counts down against the total (i.e., both user and system) CPU time
consumed by the process. (The measurement includes CPU time consumed by all
threads in the process.) At each expiration, a SIGPROF signal is generated.
In conjunction with ITIMER_VIRTUAL, this timer can be used to profile user and
system CPU time consumed by the process.
2、
Timer values are defined by the following structures:
struct itimerval {
struct timeval it_interval; /* Interval for periodic timer */
struct timeval it_value; /* Time until next expiration */
};
struct timeval {
time_t tv_sec; /* seconds */
suseconds_t tv_usec; /* microseconds */
};
3、
#include <stdio.h>
#include <sys/time.h>
#include <unistd.h>
int main()
{
struct itimerval myit = {{0,0},{3,0}};
setitimer(ITIMER_REAL,&myit,NULL);
while(1)
{
printf("1111111!\n");
sleep(1);
}
return 0;
}
4、實現了一個alarm功能
