include/wvtimestream.h

   1 /* -*- Mode: C++ -*-
   2  * Worldvisions Weaver Software:
   3  *   Copyright (C) 1997-2002 Net Integration Technologies, Inc.
   4  *
   5  */
   6 #ifndef __WVTIMESTREAM_H
   7 #define __WVTIMESTREAM_H
   8
   9 #include "wvtimeutils.h"
  10 #include "wvstream.h"
  11
  12 /**
  13  * WvTimeStream causes select() to be true after a configurable number
  14  * of milliseconds.  Because programs using WvStream make no guarantees
  15  * about how often select() will be called, WvTimeStream tries to adjust
  16  * its timing to a correct _average_ number of milliseconds per tick.
  17  *
  18  * For example, if ms_per_tick=100, WvTimeStream will tick 10 times in one
  19  * second.  However, there may be a few milliseconds of difference
  20  * ("jitter") for each individual tick, due to random system delays.
  21  */
  22 class WvTimeStream : public WvStream
  23 {
  24     WvTime last;
  25     WvTime next;
  26     time_t ms_per_tick;
  27
  28 public:
  29     WvTimeStream();
  30
  31     /**
  32      * Every 'msec' milliseconds, select() will return true on this
  33      * stream.  if 'msec' is 0 (or less), the timer is disabled.
  34      *
  35      * Be careful when mixing alarm() with this. You can know whether
  36      * it was the alarm or if you had a timer event by looking at
  37      * alarm_was_ticking. But the alarm() has priority, so if there's
  38      * always an alarm, the timer event never gets to run. Calling
  39      * alarm(0) in the callback unconditionally would thus be a bad
  40      * idea, or even with an unsuitably small number (say, less than
  41      * the time it takes to go back into select()). So don't do it.
  42      */
  43     void set_timer(time_t msec);
  44
  45     virtual bool isok() const;
  46     virtual void pre_select(SelectInfo &si);
  47     virtual bool post_select(SelectInfo &si);
  48     virtual void execute();
  49
  50 public:
  51     const char *wstype() const { return "WvTimeStream"; }
  52 };
  53
  54
  55 #endif // __WVTIMESTREAM_H