NAME

getitimer, setitimer - get or set value of interval timer

SYNOPSIS

#include <sys/time.h>

int getitimer(int which, struct itimerval * value);
int setitimer(int which, const struct itimerval * value, struct itimerval * ovalue);

DESCRIPTION

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( ) 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 * /

it_value indicates the time to the next timer expiration. it_interval specifies a value to be used in reloading it_value when the timer expires. Setting it_value to zero disables a timer, regardless of the value of it_interval. Setting it_interval to zero 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:

ITIMER_REAL

Decrements in real time. A SIGALRM signal is delivered when this timer expires.

ITIMER_VIRTUAL

Decrements in process virtual time. It runs only when the process is executing. A SIGVTALRM signal is delivered when it expires.

ITIMER_PROF

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 functions, programs using this timer must be

prepared to restart interrupted functions.

ITIMER_REALPROF

Decrements in real time. It is designed to be used for real-time profiling of multithreaded programs. Each time the

ITIMER_REALPROF timer expires, one counter in a set of

counters maintained by the system for each lightweight process (lwp) is incremented. The counter corresponds to the state of the lwp at the time of the timer tick. All lwps executing in user

mode when the timer expires are interrupted into system mode. When each lwp resumes execution in user mode, if any of the elements in its set of counters are non-zero, the SIGPROF signal is delivered to the lwp. The SIGPROF signal is delivered before any other signal except SIGKILL. This signal does not interrupt any in-progress function. A siginfo structure, defined in

sys/siginfo.h, is associated with the delivery of the SIGPROF signal, and includes the following members:

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.

RETURN VALUES

If the calls succeed, a value of 0 is returned. If an error occurs, the value -1 is returned, and an error code is placed in the global variable errno.

ERRORS

getitimer( ) and setitimer( ) will fail if:

EINVAL

The specified number of seconds is greater than 100,000,000, the number of microseconds is greater than or equal to 1,000,000, or the which parameter is unrecognized.

SEE ALSO

alarm(2), gettimeofday(3C), sysconf(3C)

NOTES

The microseconds field should not be equal to or greater than one second.

setitimer( ) is independent of the alarm( ) function.

Do not use setitimer(ITIMER_REAL) with the sleep( ) routine. A sleep( ) wipes out knowledge of the user signal handler for SIGALRM.

ITIMER_PROF and ITIMER_REALPROF deliver the same signal and have different semantics. They cannot be used together.

The granularity of the resolution of alarm time is platform-dependent.