msg_rate_delay.c

[詳解]

/*++
/* NAME
/*  msg_rate_delay 3
/* SUMMARY
/*  diagnostic interface
/* SYNOPSIS
/*  #include <msg.h>
/*
/*  void    msg_rate_delay(stamp, delay, log_fn, fmt, ...)
/*  time_t  *stamp;
/*  int delay;
/*  void    (*log_fn)(const char *fmt, ...);
/*  const char *fmt;
/* DESCRIPTION
/*  msg_rate_delay() produces log output at a reduced rate: no
/*  more than one message per 'delay' seconds. It discards log
/*  output that would violate the output rate policy.
/*
/*  This is typically used to log errors accessing a cache with
/*  high-frequency access but low-value information, to avoid
/*  spamming the logfile with the same kind of message.
/*
/*  Arguments:
/* .IP stamp
/*  Time stamp of last log output; specify a zero time stamp
/*  on the first call.  This is an input-output parameter.
/*  This parameter is ignored when verbose logging is enabled
/*  or when the delay value is zero.
/* .IP delay
/*  The minimum time between log outputs; specify zero to log
/*  all output for debugging purposes.  This parameter is ignored
/*  when verbose logging is enabled.
/* .IP log_fn
/*  The function that produces log output. Typically, this will
/*  be msg_info() or msg_warn().
/* .IP fmt
/*  Format string as used with msg(3) routines.
/* SEE ALSO
/*  msg(3) diagnostics interface
/* DIAGNOSTICS
/*  Fatal errors: memory allocation problem.
/* LICENSE
/* .ad
/* .fi
/*  The Secure Mailer license must be distributed with this software.
/* AUTHOR(S)
/*  Wietse Venema
/*  IBM T.J. Watson Research
/*  P.O. Box 704
/*  Yorktown Heights, NY 10598, USA
/*--*/


/* System library. */

#include <sys_defs.h>
#include <time.h>

/* Utility library. */

#include <msg.h>
#include <vstring.h>
#include <events.h>

/* SLMs. */

#define STR(x) vstring_str(x)

/* msg_rate_delay - rate-limit message logging */

void    msg_rate_delay(time_t *stamp, int delay,
                       void (*log_fn) (const char *,...),
                       const char *fmt,...)
{
    const char *myname = "msg_rate_delay";
    static time_t saved_event_time;
    time_t  now;
    VSTRING *buf;
    va_list ap;

    /*
     * Sanity check.
     */
    if (delay < 0)
    msg_panic("%s: bad message rate delay: %d", myname, delay);

    /*
     * This function may be called frequently. Avoid an unnecessary syscall
     * if possible. Deal with the possibility that a program does not use the
     * events(3) engine, so that event_time() always produces the same
     * result.
     */
    if (msg_verbose == 0 && delay > 0) {
    if (saved_event_time == 0)
        now = saved_event_time = event_time();
    else if ((now = event_time()) == saved_event_time)
        now = time((time_t *) 0);

    /*
     * Don't log if time is too early.
     */
    if (*stamp + delay > now)
        return;
    *stamp = now;
    }

    /*
     * OK to log. This is a low-rate event, so we can afford some overhead.
     */
    buf = vstring_alloc(100);
    va_start(ap, fmt);
    vstring_vsprintf(buf, fmt, ap);
    va_end(ap);
    log_fn("%s", STR(buf));
    vstring_free(buf);
}

#ifdef TEST

 /*
  * Proof-of-concept test program: log messages but skip messages during a
  * two-second gap.
  */
#include <unistd.h>

int     main(int argc, char **argv)
{
    int     n;
    time_t  stamp = 0;

    for (n = 0; n < 6; n++) {
    msg_rate_delay(&stamp, 2, msg_info, "text here %d", n);
    sleep(1);
    }
    return (0);
}

#endif