+++ /dev/null
-.\" Copyright 7/93 by Darren Senn <sinster@scintilla.santa-clara.ca.us>
-.\" Based on a similar page Copyright 1992 by Rick Faith
-.\"
-.\" %%%LICENSE_START(FREELY_REDISTRIBUTABLE)
-.\" May be freely distributed
-.\" %%%LICENSE_END
-.\"
-.\" Modified Tue Oct 22 00:22:35 EDT 1996 by Eric S. Raymond <esr@thyrsus.com>
-.\" 2005-04-06 mtk, Matthias Lang <matthias@corelatus.se>
-.\" Noted MAX_SEC_IN_JIFFIES ceiling
-.\"
-.TH GETITIMER 2 2014-07-08 "Linux" "Linux Programmer's Manual"
-.SH NAME
-getitimer, setitimer \- get or set value of an interval timer
-.SH SYNOPSIS
-.nf
-.B #include <sys/time.h>
-.sp
-.BI "int getitimer(int " which ", struct itimerval *" curr_value );
-.br
-.BI "int setitimer(int " which ", const struct itimerval *" new_value ,
-.BI " struct itimerval *" old_value );
-.fi
-.SH DESCRIPTION
-The system provides each process with three interval timers,
-each decrementing in a distinct time domain.
-When a timer expires, a signal is sent to the
-process, and the timer is reset to the specified interval (if nonzero).
-.TP 1.5i
-.B ITIMER_REAL
-decrements in real time, and delivers
-.B SIGALRM
-upon expiration.
-.TP
-.B ITIMER_VIRTUAL
-decrements only when the process is executing, and delivers
-.B SIGVTALRM
-upon expiration.
-.TP
-.B ITIMER_PROF
-decrements both when the process executes and when the system is executing
-on behalf of the process.
-Coupled with
-.BR ITIMER_VIRTUAL ,
-this timer is usually used to profile the time spent by the
-application in user and kernel space.
-.B SIGPROF
-is delivered upon expiration.
-.LP
-Timer values are defined by the following structures:
-.PD 0
-.in +4n
-.nf
-
-struct itimerval {
- struct timeval it_interval; /* Interval for periodic timer */
- struct timeval it_value; /* Time until next expiration */
-};
-
-struct timeval {
- time_t tv_sec; /* seconds */
- suseconds_t tv_usec; /* microseconds */
-};
-.fi
-.in
-.PD
-.LP
-The function
-.BR getitimer ()
-fills the structure pointed to by
-.I curr_value
-with the current value
-(i.e., the amount of time remaining until the next expiration)
-of the timer specified by
-.I which
-(one of
-.BR ITIMER_REAL ,
-.BR ITIMER_VIRTUAL ,
-or
-.BR ITIMER_PROF ).
-The subfields of the field
-.I it_value
-are set to the amount of time remaining on the timer, or zero if the timer
-is disabled.
-The
-.I it_interval
-field is set to the timer interval (period);
-a value of zero returned in (both subfields of) this field indicates
-that this is a single-shot timer.
-
-The function
-.BR setitimer ()
-sets the specified timer to the value in
-.IR new_value .
-If
-.I old_value
-is non-NULL, the old value of the timer
-(i.e., the same information as returned by
-.BR getitimer ())
-is stored there.
-.LP
-Timers decrement from
-.I it_value
-to zero, generate a signal, and reset to
-.IR it_interval .
-A timer which is set to zero
-.RI ( it_value
-is zero or the timer expires and
-.I it_interval
-is zero) stops.
-.LP
-Both
-.I tv_sec
-and
-.I tv_usec
-are significant in determining the duration of a timer.
-.LP
-Timers will never expire before the requested time,
-but may expire some (short) time afterward, which depends
-on the system timer resolution and on the system load; see
-.BR time (7).
-(But see BUGS below.)
-Upon expiration, a signal will be generated and the timer reset.
-If the timer expires while the process is active (always true for
-.BR ITIMER_VIRTUAL ),
-the signal will be delivered immediately when generated.
-Otherwise, the
-delivery will be offset by a small time dependent on the system loading.
-.SH RETURN VALUE
-On success, zero is returned.
-On error, \-1 is returned, and
-.I errno
-is set appropriately.
-.SH ERRORS
-.TP
-.B EFAULT
-.IR new_value ,
-.IR old_value ,
-or
-.I curr_value
-is not valid a pointer.
-.TP
-.B EINVAL
-.I which
-is not one of
-.BR ITIMER_REAL ,
-.BR ITIMER_VIRTUAL ,
-or
-.BR ITIMER_PROF ;
-or (since Linux 2.6.22) one of the
-.I tv_usec
-fields in the structure pointed to by
-.I new_value
-contains a value outside the range 0 to 999999.
-.SH CONFORMING TO
-POSIX.1-2001, SVr4, 4.4BSD (this call first appeared in 4.2BSD).
-POSIX.1-2008 marks
-.BR getitimer ()
-and
-.BR setitimer ()
-obsolete, recommending the use of the POSIX timers API
-.RB ( timer_gettime (2),
-.BR timer_settime (2),
-etc.) instead.
-.SH NOTES
-A child created via
-.BR fork (2)
-does not inherit its parent's interval timers.
-Interval timers are preserved across an
-.BR execve (2).
-
-POSIX.1 leaves the
-interaction between
-.BR setitimer ()
-and the three interfaces
-.BR alarm (2),
-.BR sleep (3),
-and
-.BR usleep (3)
-unspecified.
-
-The standards are silent on the meaning of the call:
-
- setitimer(which, NULL, &old_value);
-
-Many systems (Solaris, the BSDs, and perhaps others)
-treat this as equivalent to:
-
- getitimer(which, &old_value);
-
-In Linux, this is treated as being equivalent to a call in which the
-.I new_value
-fields are zero; that is, the timer is disabled.
-.IR "Don't use this Linux misfeature" :
-it is nonportable and unnecessary.
-.SH BUGS
-The generation and delivery of a signal are distinct, and
-only one instance of each of the signals listed above may be pending
-for a process.
-Under very heavy loading, an
-.B ITIMER_REAL
-timer may expire before the signal from a previous expiration
-has been delivered.
-The second signal in such an event will be lost.
-
-On Linux kernels before 2.6.16, timer values are represented in jiffies.
-If a request is made set a timer with a value whose jiffies
-representation exceeds
-.B MAX_SEC_IN_JIFFIES
-(defined in
-.IR include/linux/jiffies.h ),
-then the timer is silently truncated to this ceiling value.
-On Linux/i386 (where, since Linux 2.6.13,
-the default jiffy is 0.004 seconds),
-this means that the ceiling value for a timer is
-approximately 99.42 days.
-Since Linux 2.6.16,
-the kernel uses a different internal representation for times,
-and this ceiling is removed.
-
-On certain systems (including i386),
-Linux kernels before version 2.6.12 have a bug which will produce
-premature timer expirations of up to one jiffy under some circumstances.
-This bug is fixed in kernel 2.6.12.
-.\" 4 Jul 2005: It looks like this bug may remain in 2.4.x.
-.\" http://lkml.org/lkml/2005/7/1/165
-
-POSIX.1-2001 says that
-.BR setitimer ()
-should fail if a
-.I tv_usec
-value is specified that is outside of the range 0 to 999999.
-However, in kernels up to and including 2.6.21,
-Linux does not give an error, but instead silently
-adjusts the corresponding seconds value for the timer.
-From kernel 2.6.22 onward,
-this nonconformance has been repaired:
-an improper
-.I tv_usec
-value results in an
-.B EINVAL
-error.
-.\" Bugzilla report 25 Apr 2006:
-.\" http://bugzilla.kernel.org/show_bug.cgi?id=6443
-.\" "setitimer() should reject noncanonical arguments"
-.SH SEE ALSO
-.BR gettimeofday (2),
-.BR sigaction (2),
-.BR signal (2),
-.BR timer_create (2),
-.BR timerfd_create (2),
-.BR time (7)
-.SH COLOPHON
-This page is part of release 3.79 of the Linux
-.I man-pages
-project.
-A description of the project,
-information about reporting bugs,
-and the latest version of this page,
-can be found at
-\%http://www.kernel.org/doc/man\-pages/.
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