138 lines
5.0 KiB
Perl
138 lines
5.0 KiB
Perl
.\" Copyright (c) 1983, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)1.4.t 8.1 (Berkeley) 6/8/93
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.\"
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.sh "Timers
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.NH 3
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Real time
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.PP
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The system's notion of the current Greenwich time and the current time
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zone is set and returned by the call by the calls:
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.DS
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#include <sys/time.h>
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settimeofday(tvp, tzp);
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struct timeval *tp;
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struct timezone *tzp;
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gettimeofday(tp, tzp);
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result struct timeval *tp;
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result struct timezone *tzp;
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.DE
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where the structures are defined in \fI<sys/time.h>\fP as:
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.DS
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._f
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struct timeval {
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long tv_sec; /* seconds since Jan 1, 1970 */
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long tv_usec; /* and microseconds */
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};
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struct timezone {
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int tz_minuteswest; /* of Greenwich */
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int tz_dsttime; /* type of dst correction to apply */
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};
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.DE
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The precision of the system clock is hardware dependent.
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Earlier versions of UNIX contained only a 1-second resolution version
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of this call, which remains as a library routine:
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.DS
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time(tvsec)
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result long *tvsec;
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.DE
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returning only the tv_sec field from the \fIgettimeofday\fP call.
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.NH 3
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Interval time
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.PP
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The system provides each process with three interval timers,
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defined in \fI<sys/time.h>\fP:
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.DS
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._d
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#define ITIMER_REAL 0 /* real time intervals */
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#define ITIMER_VIRTUAL 1 /* virtual time intervals */
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#define ITIMER_PROF 2 /* user and system virtual time */
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.DE
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The ITIMER_REAL timer decrements
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in real time. It could be used by a library routine to
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maintain a wakeup service queue. A SIGALRM signal is delivered
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when this timer expires.
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.PP
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The ITIMER_VIRTUAL timer decrements in process virtual time.
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It runs only when the process is executing. A SIGVTALRM signal
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is delivered when it expires.
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.PP
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The ITIMER_PROF timer decrements both in process virtual time and when
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the system is running on behalf of the process.
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It is designed to be used by processes to statistically profile
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their execution.
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A SIGPROF signal is delivered when it expires.
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.PP
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A timer value is defined by the \fIitimerval\fP structure:
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.DS
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._f
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struct itimerval {
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struct timeval it_interval; /* timer interval */
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struct timeval it_value; /* current value */
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};
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.DE
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and a timer is set or read by the call:
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.DS
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getitimer(which, value);
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int which; result struct itimerval *value;
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setitimer(which, value, ovalue);
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int which; struct itimerval *value; result struct itimerval *ovalue;
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.DE
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The third argument to \fIsetitimer\fP specifies an optional structure
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to receive the previous contents of the interval timer.
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A timer can be disabled by specifying a timer value of 0.
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.PP
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The system rounds argument timer intervals to be not less than the
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resolution of its clock. This clock resolution can be determined
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by loading a very small value into a timer and reading the timer back to
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see what value resulted.
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.PP
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The \fIalarm\fP system call of earlier versions of UNIX is provided
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as a library routine using the ITIMER_REAL timer. The process
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profiling facilities of earlier versions of UNIX
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remain because
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it is not always possible to guarantee
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the automatic restart of system calls after
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receipt of a signal.
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The \fIprofil\fP call arranges for the kernel to begin gathering
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execution statistics for a process:
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.DS
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profil(buf, bufsize, offset, scale);
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result char *buf; int bufsize, offset, scale;
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.DE
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This begins sampling of the program counter, with statistics maintained
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in the user-provided buffer.
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