GETITIMER(2)
NAME
getitimer, setitimer − get/set value of interval timer
USAGE
#include <sys/time.h>
#define ITIMER_REAL0/* real time intervals */ #define ITIMER_VIRTUAL 1 /* virtual time intervals */ #define ITIMER_PROF 2 /* user and system virtual time */
getitimer(which, value) int which; struct itimerval *value;
setitimer(which, value, ovalue) int which; struct itimerval *value, *ovalue;
DESCRIPTION
The system provides each process with three interval timers, defined in <sys/time.h>. The getitimer call returns the current value for the timer specified in the argument which, while the setitimer call sets the value of a timer. (Getitimer may also return the previous value of the timer.)
A timer value comes from the itimerval structure:
struct itimerval { structtimeval it_interval;/* timer interval */ structtimeval it_value; /* current value */ };
If it_value is non-zero, it indicates the time to the next timer expiration. If it_interval is non-zero, it specifies a value to be used in reloading it_value when the timer expires. Setting it_value to zero disables a timer. Setting it_interval to zero causes a timer to be disabled after its next expiration (assuming it_value is non-zero).
Time values smaller than the resolution of the system clock (4 μseconds on DOMAIN systems) are rounded up to this resolution.
The ITIMER_REAL timer decrements in real time and delivers a SIGALRM signal when it expires.
The ITIMER_VIRTUAL timer decrements in process virtual time. It runs only when the process is executing, and delivers a SIGVTALRM signal when it expires.
The ITIMER_PROF timer decrements both in process virtual time and when the system is running on behalf of the process. It is designed to be used by interpreters in statistically profiling the execution of interpreted programs. Each time the ITIMER_PROF timer expires, the SIGPROF signal is delivered. Because this signal may interrupt in-progress system calls, programs using this timer must be prepared to restart interrupted system calls.
NOTES
Three macros for manipulating time values are defined in <sys/time.h>. Timerclear sets a time value to zero, timerisset tests if a time value is non-zero, and timercmp compares two time values (>= and <= do not work with this macro).
RETURN VALUE
A successful call returns zero. A failed call returns -1 and sets errno as indicated below.
ERRORS
The possible errors are:
[EFAULT] The value structure specified a bad address.
[EINVAL] A value structure specified that a time was too large to be handled.