May 16, 1995
freebsd-manpages
Manual pages for a GNU/kFreeBSD system
NAME
getitimer, setitimer - get/set value of interval timer
LIBRARY
.Lb libc
SYNOPSIS
.In sys/time.h
.Fd #define ITIMER_REAL 0
.Fd #define ITIMER_VIRTUAL 1
.Fd #define ITIMER_PROF 2 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 three interval timers, defined in
.In sys/time.h . The
.In sys/time.h . The
getitimer
system call returns the current value for the timer specified in which in the structure at value. The setitimer
system call sets a timer to the specified value (returning the previous value of the timer if ovalue is not a null pointer).
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, regardless of the value of it_interval. 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 maximum number of seconds allowed for it_interval and it_value in
setitimer
is 100000000.NOTES
Three macros for manipulating time values are defined in
.In sys/time.h . The
.In sys/time.h . The
timerclear
macro sets a time value to zero, timerisset
tests if a time value is non-zero, and timercmp
compares two time values.RETURN VALUES
.Rv -std
ERRORS
The
getitimer
and setitimer
system calls will fail if:
[EFAULT ] |
|
The value argument specified a bad address. | |
[EINVAL ] |
|
The value argument specified a time that was too large to be handled. |
SEE ALSO
HISTORY
The
getitimer
system call appeared in BSD 4.2 .