getitimer, setitimer - get or set value of interval timer
#include <sys/time.h> int getitimer(int which, struct itimerval *value);
int setitimer(int which, const struct itimerval *value, struct itimerval *ovalue);
The system provides each process with four interval timers, defined in <sys/time.h>. The getitimer() function stores the current value of the timer specified by which into the structure pointed to by value. The setitimer() function call sets the value of the timer specified by which to the value specified in the structure pointed to by value, and if ovalue is not NULL, stores the previous value of the timer in the structure pointed to by ovalue.
A timer value is defined by the itimerval structure (see gettimeofday(3C)) for the definition of timeval), which includes the following members:
struct timeval it_interval; /* timer interval */ struct timeval it_value; /* current value */
The it_value member indicates the time to the next timer expiration. The it_interval member specifies a value to be used in reloading it_value when the timer expires. Setting it_value to 0 disables a timer, regardless of the value of it_interval. Setting it_interval to 0 disables a timer after its next expiration (assuming it_value is non-zero).
Time values smaller than the resolution of the system clock are rounded up to the resolution of the system clock, except for ITIMER_REALPROF, whose values are rounded up to the resolution of the profiling clock. The four timers are as follows:
si_tstamp; /* high resolution timestamp */ si_syscall; /* current syscall */ si_nsysarg; /* number of syscall arguments */ si_sysarg; /* actual syscall arguments */ si_fault; /* last fault type */ si_faddr; /* last fault address */ si_mstate; /* ticks in each microstate */
The enumeration of microstates (indices into si_mstate) is defined in <sys/msacct.h>.
Upon successful completion, 0 is returned. Otherwise, -1 is returned and errno is set to indicate the error.
The getitimer() and setitimer() functions will fail if:
See attributes(5) for descriptions of the following attributes:
alarm(2), gettimeofday(3C), sleep(3C), sysconf(3C), attributes(5), standards(5)
The microseconds field should not be equal to or greater than one second.
The setitimer() function is independent of the alarm() function.
Do not use setitimer(ITIMER_REAL) with the sleep() routine. A sleep(3C) call wipes out knowledge of the user signal handler for SIGALRM.
The ITIMER_PROF and ITIMER_REALPROF timers deliver the same signal and have different semantics. They cannot be used together.
The granularity of the resolution of alarm time is platform-dependent.
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Created 1996-2023 by Maxim Chirkov
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