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GETITIMER(2) | System Calls Manual | GETITIMER(2) |
NAME¶
getitimer
,
setitimer
—
get/set value of interval timer
LIBRARY¶
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¶
Thegetitimer
() 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), sigaction(2), clocks(7)HISTORY¶
Thegetitimer
() system call appeared in
4.2BSD.May 16, 1995 | Debian |