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GETITIMER(2) | System Calls Manual | GETITIMER(2) |
NAME¶
getitimer, setitimer — get/set value of interval timerLIBRARY¶
Standard C Library (libc, -lc)SYNOPSIS¶
#include <sys/time.h> #define ITIMER_REAL 0#define ITIMER_VIRTUAL 1
#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 <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 */ };
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 <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¶
Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.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¶
gettimeofday(2), select(2), sigvec(2), clocks(7)HISTORY¶
The getitimer() system call appeared in 4.2BSD.May 16, 1995 | Debian |