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| author | Michael Kerrisk <mtk.manpages@gmail.com> | 2004-11-03 13:51:07 +0000 |
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| committer | Michael Kerrisk <mtk.manpages@gmail.com> | 2004-11-03 13:51:07 +0000 |
| commit | fea681dafb1363a154b7fc6d59baa83d2a9ebc5c (patch) | |
| tree | 8ea275c0f242af739617d0afc3e1b16c4eff3dc2 /man2/getitimer.2 | |
| download | man-pages-fea681dafb1363a154b7fc6d59baa83d2a9ebc5c.tar.gz | |
Import of man-pages 1.70man-pages-1.70
Diffstat (limited to 'man2/getitimer.2')
| -rw-r--r-- | man2/getitimer.2 | 147 |
1 files changed, 147 insertions, 0 deletions
diff --git a/man2/getitimer.2 b/man2/getitimer.2 new file mode 100644 index 0000000000..530a14605b --- /dev/null +++ b/man2/getitimer.2 @@ -0,0 +1,147 @@ +.\" Copyright 7/93 by Darren Senn <sinster@scintilla.santa-clara.ca.us> +.\" Based on a similar page Copyright 1992 by Rick Faith +.\" May be freely distributed +.\" Modified Tue Oct 22 00:22:35 EDT 1996 by Eric S. Raymond <esr@thyrsus.com> +.TH GETITIMER 2 1993-08-05 "Linux 0.99.11" "Linux Programmer's Manual" +.SH NAME +getitimer, setitimer \- get or set value of an interval timer +.SH SYNOPSIS +.PD 0 +.HP +.B #include <sys/time.h> +.sp +.HP +.B int getitimer(int +.IB which , +.B struct itimerval +.BI * value ); +.HP +.B int setitimer(int +.IB which , +.B const struct itimerval +.BI * value , +.B struct itimerval +.BI * ovalue ); +.PD +.SH DESCRIPTION +The system provides each process with three interval timers, each decrementing +in a distinct time domain. When any timer expires, a signal is sent to the +process, and the timer (potentially) restarts. +.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 +.RS .5i +.nf +struct itimerval { + struct timeval it_interval; /* next value */ + struct timeval it_value; /* current value */ +}; +struct timeval { + long tv_sec; /* seconds */ + long tv_usec; /* microseconds */ +}; +.fi +.RE +.PD +.LP +The function +.B getitimer +fills the structure indicated by +.I value +with the current setting for the timer indicated by +.I which +(one of +.BR ITIMER_REAL , +.BR ITIMER_VIRTUAL , +or +.BR ITIMER_PROF ). +The element +.B it_value +is set to the amount of time remaining on the timer, or zero if the timer +is disabled. Similarly, +.B it_interval +is set to the reset value. +The function +.B setitimer +sets the indicated timer to the value in +.IR value . +If +.I ovalue +is nonzero, the old value of the timer 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, +instead expiring some short, constant time afterwards, dependent +on the system timer resolution (currently 10ms). 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_VIRT ) +the signal will be delivered immediately when generated. Otherwise the +delivery will be offset by a small time dependent on the system loading. +.LP +.SH "RETURN VALUE" +On success, zero is returned. On error, \-1 is returned, and +.I errno +is set appropriately. +.SH ERRORS +.TP +.B EFAULT +.I value +or +.I ovalue +are not valid pointers. +.TP +.B EINVAL +.I which +is not one of +.BR ITIMER_REAL , +.BR ITIMER_VIRT , +or +.BR ITIMER_PROF . +.SH "CONFORMING TO" +SVr4, 4.4BSD (This call first appeared in 4.2BSD). +.SH "SEE ALSO" +.BR gettimeofday (2), +.BR sigaction (2), +.BR signal (2) +.SH BUGS +Under Linux, the generation and delivery of a signal are distinct, and +there each signal is permitted only one outstanding event. It's therefore +conceivable that under pathologically heavy loading, +.B ITIMER_REAL +will expire before the signal from a previous expiration has been delivered. +The second signal in such an event will be lost. |