git.distorted.org.uk Git - u/mdw/putty/blob - timing.c

   1 /*
   2  * timing.c
   3  *
   4  * This module tracks any timers set up by schedule_timer(). It
   5  * keeps all the currently active timers in a list; it informs the
   6  * front end of when the next timer is due to go off if that
   7  * changes; and, very importantly, it tracks the context pointers
   8  * passed to schedule_timer(), so that if a context is freed all
   9  * the timers associated with it can be immediately annulled.
  10  */
  11
  12 #include <assert.h>
  13 #include <stdio.h>
  14
  15 #include "putty.h"
  16 #include "tree234.h"
  17
  18 struct timer {
  19     timer_fn_t fn;
  20     void *ctx;
  21     long now;
  22 };
  23
  24 static tree234 *timers = NULL;
  25 static long now = 0L;
  26
  27 static int compare_timers(void *av, void *bv)
  28 {
  29     struct timer *a = (struct timer *)av;
  30     struct timer *b = (struct timer *)bv;
  31     long at = a->now - now;
  32     long bt = b->now - now;
  33
  34     if (at < bt)
  35         return -1;
  36     else if (at > bt)
  37         return +1;
  38
  39     /*
  40      * Failing that, compare on the other two fields, just so that
  41      * we don't get unwanted equality.
  42      */
  43 #ifdef __LCC__
  44     /* lcc won't let us compare function pointers. Legal, but annoying. */
  45     {
  46         int c = memcmp(&a->fn, &b->fn, sizeof(a->fn));
  47         if (c < 0)
  48             return -1;
  49         else if (c > 0)
  50             return +1;
  51     }
  52 #else
  53     if (a->fn < b->fn)
  54         return -1;
  55     else if (a->fn > b->fn)
  56         return +1;
  57 #endif
  58
  59     if (a->ctx < b->ctx)
  60         return -1;
  61     else if (a->ctx > b->ctx)
  62         return +1;
  63
  64     /*
  65      * Failing _that_, the two entries genuinely are equal, and we
  66      * never have a need to store them separately in the tree.
  67      */
  68     return 0;
  69 }
  70
  71 static int compare_timer_contexts(void *av, void *bv)
  72 {
  73     struct timer *at = (struct timer *)av;
  74     struct timer *bt = (struct timer *)bv;
  75     char *a = (char *)at->ctx;
  76     char *b = (char *)bt->ctx;
  77     if (a < b)
  78         return -1;
  79     else if (a > b)
  80         return +1;
  81     return 0;
  82 }
  83
  84 static void init_timers(void)
  85 {
  86     if (!timers) {
  87         timers = newtree234(compare_timers);
  88         now = GETTICKCOUNT();
  89     }
  90 }
  91
  92 long schedule_timer(int ticks, timer_fn_t fn, void *ctx)
  93 {
  94     long when;
  95     struct timer *t, *first;
  96
  97     init_timers();
  98
  99     when = ticks + GETTICKCOUNT();
 100
 101     /*
 102      * Just in case our various defences against timing skew fail
 103      * us: if we try to schedule a timer that's already in the
 104      * past, we instead schedule it for the immediate future.
 105      */
 106     if (when - now <= 0)
 107         when = now + 1;
 108
 109     t = snew(struct timer);
 110     t->fn = fn;
 111     t->ctx = ctx;
 112     t->now = when;
 113
 114     if (t != add234(timers, t)) {
 115         sfree(t);                      /* identical timer already exists */
 116     }
 117
 118     first = (struct timer *)index234(timers, 0);
 119     if (first == t) {
 120         /*
 121          * This timer is the very first on the list, so we must
 122          * notify the front end.
 123          */
 124         timer_change_notify(first->now);
 125     }
 126
 127     return when;
 128 }
 129
 130 /*
 131  * Call to run any timers whose time has reached the present.
 132  * Returns the time (in ticks) expected until the next timer after
 133  * that triggers.
 134  */
 135 int run_timers(long anow, long *next)
 136 {
 137     struct timer *first;
 138
 139     init_timers();
 140
 141 #ifdef TIMING_SYNC
 142     /*
 143      * In this ifdef I put some code which deals with the
 144      * possibility that `anow' disagrees with GETTICKCOUNT by a
 145      * significant margin. Our strategy for dealing with it differs
 146      * depending on platform, because on some platforms
 147      * GETTICKCOUNT is more likely to be right whereas on others
 148      * `anow' is a better gold standard.
 149      */
 150     {
 151         long tnow = GETTICKCOUNT();
 152
 153         if (tnow + TICKSPERSEC/50 - anow < 0 ||
 154             anow + TICKSPERSEC/50 - tnow < 0
 155             ) {
 156 #if defined TIMING_SYNC_ANOW
 157             /*
 158              * If anow is accurate and the tick count is wrong,
 159              * this is likely to be because the tick count is
 160              * derived from the system clock which has changed (as
 161              * can occur on Unix). Therefore, we resolve this by
 162              * inventing an offset which is used to adjust all
 163              * future output from GETTICKCOUNT.
 164              *
 165              * A platform which defines TIMING_SYNC_ANOW is
 166              * expected to have also defined this offset variable
 167              * in (its platform-specific adjunct to) putty.h.
 168              * Therefore we can simply reference it here and assume
 169              * that it will exist.
 170              */
 171             tickcount_offset += anow - tnow;
 172 #elif defined TIMING_SYNC_TICKCOUNT
 173             /*
 174              * If the tick count is more likely to be accurate, we
 175              * simply use that as our time value, which may mean we
 176              * run no timers in this call (because we got called
 177              * early), or alternatively it may mean we run lots of
 178              * timers in a hurry because we were called late.
 179              */
 180             anow = tnow;
 181 #else
 182 /*
 183  * Any platform which defines TIMING_SYNC must also define one of the two
 184  * auxiliary symbols TIMING_SYNC_ANOW and TIMING_SYNC_TICKCOUNT, to
 185  * indicate which measurement to trust when the two disagree.
 186  */
 187 #error TIMING_SYNC definition incomplete
 188 #endif
 189         }
 190     }
 191 #endif
 192
 193     now = anow;
 194
 195     while (1) {
 196         first = (struct timer *)index234(timers, 0);
 197
 198         if (!first)
 199             return FALSE;              /* no timers remaining */
 200
 201         if (first->now - now <= 0) {
 202             /*
 203              * This timer is active and has reached its running
 204              * time. Run it.
 205              */
 206             delpos234(timers, 0);
 207             first->fn(first->ctx, first->now);
 208             sfree(first);
 209         } else {
 210             /*
 211              * This is the first still-active timer that is in the
 212              * future. Return how long it has yet to go.
 213              */
 214             *next = first->now;
 215             return TRUE;
 216         }
 217     }
 218 }
 219
 220 /*
 221  * Call to expire all timers associated with a given context.
 222  */
 223 void expire_timer_context(void *ctx)
 224 {
 225     struct timer *ptr;
 226     struct timer exemplar;
 227
 228     if (!timers) return;
 229
 230     exemplar.ctx = ctx;
 231     /* don't care about initialisation of other members */
 232
 233     /* Dispose of all timers with this context */
 234     while ((ptr = (struct timer *)find234(timers, &exemplar,
 235                                           compare_timer_contexts))) {
 236         del234(timers, ptr);
 237         sfree(ptr);
 238     }
 239
 240     /* Dispose of timer tree itself if none are left */
 241     if (count234(timers) == 0) {
 242         freetree234(timers);
 243         timers = NULL;
 244     }
 245 }