getitimer(2) System Calls Manual getitimer(2)
Name
getitimer, setitimer - get or set value of interval timer
Syntax
#include <sys/time.h>
#define ITIMER_REAL 0 /* real time intervals */
#define ITIMER_VIRTUAL 1 /* virtual time intervals */
#define ITIMER_PROF 2 /* user and system virtual time */
getitimer(which, value)
int which;
struct itimerval *value;
setitimer(which, value, ovalue)
int which;
struct itimerval *value, *ovalue;
Description
The system provides each process with three interval timers, defined in <sys/time.h>. The call returns the current value for the timer
specified in which, while the call sets the value of a timer (optionally, returning the previous value of the timer). The upper limit for
time values are as follows:
For VAX machines, 10millisec * 0x7fffffff (about 256 days)
For RISC machines, 3.906 millsec * 0x7fffffff (about 97 days)
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 nonzero, it indicates the time to the next timer expiration. If it_interval is nonzero, 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 nonzero).
Time values smaller than the resolution of the system clock are rounded up to this resolution (on MIPS, 3.906 milliseconds; on VAX, 10 mil-
liseconds).
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.
Three macros for manipulating time values are defined in <sys/time.h>. The timerclear sets a time value to zero, timerisset tests if a
time value is nonzero, and timercmp compares two time values (beware that >= and <= do not work with this macro).
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.
Diagnostics
The possible errors are:
[EFAULT] The value structure specified a bad address.
[EINVAL] A value structure specified a time that was too large to be handled.
See Also
gettimeofday(2), sigvec(2), pause(3)
getitimer(2)
