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GETITIMER(2) System Calls Manual GETITIMER(2)


getitimer, setitimer, timerclear, timerisset, timercmp, timersub, timeraddget/set value of interval timer


#include <sys/time.h>

#define ITIMER_REAL 0
#define ITIMER_PROF 2
getitimer(int which, struct itimerval *value);
setitimer(int which, const struct itimerval *value, struct itimerval *ovalue);
timerclear(struct timeval *);
timerisset(struct timeval *);
timercmp(struct timeval *a, struct timeval *b, CMP);
timersub(struct timeval *a, struct timeval *b, struct timeval *res);
timeradd(struct timeval *a, struct timeval *b, struct timeval *res);


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 which in the structure at value. The setitimer() call sets a timer to the specified value (returning the previous value of the timer if ovalue is non-null).
A timer value is defined by the itimerval structure:
struct itimerval { 
	struct	timeval it_interval;	/* timer interval */ 
	struct	timeval 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 0 disables a timer. Setting it_interval to 0 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 are rounded up to this resolution (typically 10 milliseconds).
The ITIMER_REAL timer decrements in real time. A SIGALRM signal is delivered when this timer expires.
The ITIMER_VIRTUAL timer decrements in process virtual time. It runs only when the process is executing. A SIGVTALRM signal is delivered 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.
The remaining five functions are in fact macros for manipulating time values, defined in <sys/time.h>.
timerclear(a) sets the time value in a to zero.
timerisset(a) tests if the time value in a is non-zero.
timercmp(a, b, CMP) compares two time values in the form a CMP b, where CMP is <, <=, ==, !=, >=, or > .
timersub(a, b, res) subtracts a - b and stores the result in res.
timeradd(a, b, res) adds two timers and stores the result in res.


Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.


getitimer() and setitimer() will fail if:
The value parameter specified a bad address.
An unrecognized value for which was specified.
In addition, setitimer() may return the following error:
value or ovalue specified a time that was too large to be handled.


clock_gettime(2), gettimeofday(2), poll(2), select(2), sigaction(2)


The getitimer() and setitimer() functions conform to IEEE Std 1003.1-2008 (“POSIX.1”).


The getitimer() and setitimer() system calls first appeared in 4.1cBSD.
November 10, 2015 OpenBSD-current