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Annotation of 43BSDReno/share/doc/ps1/06.sysman/1.4.t, revision 1.1

1.1     ! root        1: .\" Copyright (c) 1983 Regents of the University of California.
        !             2: .\" All rights reserved.  The Berkeley software License Agreement
        !             3: .\" specifies the terms and conditions for redistribution.
        !             4: .\"
        !             5: .\"    @(#)1.4.t       6.2 (Berkeley) 5/12/86
        !             6: .\"
        !             7: .sh "Timers
        !             8: .NH 3
        !             9: Real time
        !            10: .PP
        !            11: The system's notion of the current Greenwich time and the current time
        !            12: zone is set and returned by the call by the calls:
        !            13: .DS
        !            14: #include <sys/time.h>
        !            15: 
        !            16: settimeofday(tvp, tzp);
        !            17: struct timeval *tp;
        !            18: struct timezone *tzp;
        !            19: 
        !            20: gettimeofday(tp, tzp);
        !            21: result struct timeval *tp;
        !            22: result struct timezone *tzp;
        !            23: .DE
        !            24: where the structures are defined in \fI<sys/time.h>\fP as:
        !            25: .DS
        !            26: ._f
        !            27: struct timeval {
        !            28:        long    tv_sec; /* seconds since Jan 1, 1970 */
        !            29:        long    tv_usec;        /* and microseconds */
        !            30: };
        !            31: 
        !            32: struct timezone {
        !            33:        int     tz_minuteswest; /* of Greenwich */
        !            34:        int     tz_dsttime;     /* type of dst correction to apply */
        !            35: };
        !            36: .DE
        !            37: The precision of the system clock is hardware dependent.
        !            38: Earlier versions of UNIX contained only a 1-second resolution version
        !            39: of this call, which remains as a library routine:
        !            40: .DS
        !            41: time(tvsec)
        !            42: result long *tvsec;
        !            43: .DE
        !            44: returning only the tv_sec field from the \fIgettimeofday\fP call.
        !            45: .NH 3
        !            46: Interval time
        !            47: .PP
        !            48: The system provides each process with three interval timers,
        !            49: defined in \fI<sys/time.h>\fP:
        !            50: .DS
        !            51: ._d
        !            52: #define        ITIMER_REAL     0       /* real time intervals */
        !            53: #define        ITIMER_VIRTUAL  1       /* virtual time intervals */
        !            54: #define        ITIMER_PROF     2       /* user and system virtual time */
        !            55: .DE
        !            56: The ITIMER_REAL timer decrements
        !            57: in real time.  It could be used by a library routine to
        !            58: maintain a wakeup service queue.  A SIGALRM signal is delivered
        !            59: when this timer expires.
        !            60: .PP
        !            61: The ITIMER_VIRTUAL timer decrements in process virtual time.
        !            62: It runs only when the process is executing.  A SIGVTALRM signal
        !            63: is delivered when it expires.
        !            64: .PP
        !            65: The ITIMER_PROF timer decrements both in process virtual time and when
        !            66: the system is running on behalf of the process.
        !            67: It is designed to be used by processes to statistically profile
        !            68: their execution.
        !            69: A SIGPROF signal is delivered when it expires.
        !            70: .PP
        !            71: A timer value is defined by the \fIitimerval\fP structure:
        !            72: .DS
        !            73: ._f
        !            74: struct itimerval {
        !            75:        struct  timeval it_interval;    /* timer interval */
        !            76:        struct  timeval it_value;       /* current value */
        !            77: };
        !            78: .DE
        !            79: and a timer is set or read by the call:
        !            80: .DS
        !            81: getitimer(which, value);
        !            82: int which; result struct itimerval *value;
        !            83: 
        !            84: setitimer(which, value, ovalue);
        !            85: int which; struct itimerval *value; result struct itimerval *ovalue;
        !            86: .DE
        !            87: The third argument to \fIsetitimer\fP specifies an optional structure
        !            88: to receive the previous contents of the interval timer.
        !            89: A timer can be disabled by specifying a timer value of 0.
        !            90: .PP
        !            91: The system rounds argument timer intervals to be not less than the
        !            92: resolution of its clock.  This clock resolution can be determined
        !            93: by loading a very small value into a timer and reading the timer back to
        !            94: see what value resulted.
        !            95: .PP
        !            96: The \fIalarm\fP system call of earlier versions of UNIX is provided
        !            97: as a library routine using the ITIMER_REAL timer.  The process
        !            98: profiling facilities of earlier versions of UNIX
        !            99: remain because
        !           100: it is not always possible to guarantee
        !           101: the automatic restart of system calls after 
        !           102: receipt of a signal.
        !           103: The \fIprofil\fP call arranges for the kernel to begin gathering
        !           104: execution statistics for a process:
        !           105: .DS
        !           106: profil(buf, bufsize, offset, scale);
        !           107: result char *buf; int bufsize, offset, scale;
        !           108: .DE
        !           109: This begins sampling of the program counter, with statistics maintained
        !           110: in the user-provided buffer.

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