GETITIMER(2) BSD Programmer's Manual GETITIMER(2)NAME
getitimer, setitimer - get/set value of interval timer
SYNOPSIS
#include <time.h>
int
getitimer(int which, struct itimerval *value);
int
setitimer(int which, struct itimerval *value, struct itimerval *ovalue);
DESCRIPTION
The system provides each process with three interval timers: ITIMER_REAL,
ITIMER_VIRTUAL and ITIMER_PROF.
The getitimer() call returns the current value for the timer specified in
which in the structure at value.
The setitimer() call sets the timer specified in which to the specified
value, and returns the previous value of the timer if ovalue is not NULL.
The which parameter is one of the following:
ITIMER_REAL
This timer decrements in real time. A SIGALRM signal is delivered
when this timer expires.
ITIMER_VIRTUAL
This timer decrements in process virtual time. It runs only when
the process is executing. A SIGVTALRM signal is delivered when it
expires.
ITIMER_PROF
This timer decrements both in process virtual time and when the sys-
tem is running on behalf of the process. It is designed to be used
by interpreters in statistically profiling the execution of inter-
preted 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.
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 expira-
tion. 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 dis-
ables 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).
NOTES
Three macros for manipulating time values are defined in <time.h>.
Timerclear sets a time value to zero, timerisset tests if a time value is
non-zero, and timercmp compares two time values.
RETURN VALUES
If the calls succeed, a value of 0 is returned. If an error occurs, the
value -1 is returned, and a more precise error code is placed in the
global variable errno.
ERRORSGetitimer() and setitimer() will fail if:
[EFAULT] The value parameter specified a bad address.
[EINVAL] A value parameter specified a time that was too large to be
handled.
SEE ALSOselect(2), sigvec(2), gettimeofday(2)HISTORY
The getitimer function call appeared in 4.2BSD.
4.2 Berkeley Distribution May 16, 1995 2
