checking in all the old panacean stuff

sFTPlugins/psftp/TIMING.C

@@ -0,0 +1,243 @@
+/*
+ * timing.c
+ * 
+ * This module tracks any timers set up by schedule_timer(). It
+ * keeps all the currently active timers in a list; it informs the
+ * front end of when the next timer is due to go off if that
+ * changes; and, very importantly, it tracks the context pointers
+ * passed to schedule_timer(), so that if a context is freed all
+ * the timers associated with it can be immediately annulled.
+ */
+
+#include <assert.h>
+#include <stdio.h>
+
+#include "putty.h"
+#include "tree234.h"
+
+struct timer {
+    timer_fn_t fn;
+    void *ctx;
+    long now;
+};
+
+static tree234 *timers = NULL;
+static tree234 *timer_contexts = NULL;
+static long now = 0L;
+
+static int compare_timers(void *av, void *bv)
+{
+    struct timer *a = (struct timer *)av;
+    struct timer *b = (struct timer *)bv;
+    long at = a->now - now;
+    long bt = b->now - now;
+
+    if (at < bt)
+	return -1;
+    else if (at > bt)
+	return +1;
+
+    /*
+     * Failing that, compare on the other two fields, just so that
+     * we don't get unwanted equality.
+     */
+#ifdef __LCC__
+    /* lcc won't let us compare function pointers. Legal, but annoying. */
+    {
+	int c = memcmp(&a->fn, &b->fn, sizeof(a->fn));
+	if (c < 0)
+	    return -1;
+	else if (c > 0)
+	    return +1;
+    }
+#else    
+    if (a->fn < b->fn)
+	return -1;
+    else if (a->fn > b->fn)
+	return +1;
+#endif
+
+    if (a->ctx < b->ctx)
+	return -1;
+    else if (a->ctx > b->ctx)
+	return +1;
+
+    /*
+     * Failing _that_, the two entries genuinely are equal, and we
+     * never have a need to store them separately in the tree.
+     */
+    return 0;
+}
+
+static int compare_timer_contexts(void *av, void *bv)
+{
+    char *a = (char *)av;
+    char *b = (char *)bv;
+    if (a < b)
+	return -1;
+    else if (a > b)
+	return +1;
+    return 0;
+}
+
+static void init_timers(void)
+{
+    if (!timers) {
+	timers = newtree234(compare_timers);
+	timer_contexts = newtree234(compare_timer_contexts);
+	now = GETTICKCOUNT();
+    }
+}
+
+long schedule_timer(int ticks, timer_fn_t fn, void *ctx)
+{
+    long when;
+    struct timer *t, *first;
+
+    init_timers();
+
+    when = ticks + GETTICKCOUNT();
+
+    /*
+     * Just in case our various defences against timing skew fail
+     * us: if we try to schedule a timer that's already in the
+     * past, we instead schedule it for the immediate future.
+     */
+    if (when - now <= 0)
+	when = now + 1;
+
+    t = snew(struct timer);
+    t->fn = fn;
+    t->ctx = ctx;
+    t->now = when;
+
+    if (t != add234(timers, t)) {
+	sfree(t);		       /* identical timer already exists */
+    } else {
+	add234(timer_contexts, t->ctx);/* don't care if this fails */
+    }
+
+    first = (struct timer *)index234(timers, 0);
+    if (first == t) {
+	/*
+	 * This timer is the very first on the list, so we must
+	 * notify the front end.
+	 */
+	timer_change_notify(first->now);
+    }
+
+    return when;
+}
+
+/*
+ * Call to run any timers whose time has reached the present.
+ * Returns the time (in ticks) expected until the next timer after
+ * that triggers.
+ */
+int run_timers(long anow, long *next)
+{
+    struct timer *first;
+
+    init_timers();
+
+#ifdef TIMING_SYNC
+    /*
+     * In this ifdef I put some code which deals with the
+     * possibility that `anow' disagrees with GETTICKCOUNT by a
+     * significant margin. Our strategy for dealing with it differs
+     * depending on platform, because on some platforms
+     * GETTICKCOUNT is more likely to be right whereas on others
+     * `anow' is a better gold standard.
+     */
+    {
+	long tnow = GETTICKCOUNT();
+
+	if (tnow + TICKSPERSEC/50 - anow < 0 ||
+	    anow + TICKSPERSEC/50 - tnow < 0
+	    ) {
+#if defined TIMING_SYNC_ANOW
+	    /*
+	     * If anow is accurate and the tick count is wrong,
+	     * this is likely to be because the tick count is
+	     * derived from the system clock which has changed (as
+	     * can occur on Unix). Therefore, we resolve this by
+	     * inventing an offset which is used to adjust all
+	     * future output from GETTICKCOUNT.
+	     * 
+	     * A platform which defines TIMING_SYNC_ANOW is
+	     * expected to have also defined this offset variable
+	     * in (its platform-specific adjunct to) putty.h.
+	     * Therefore we can simply reference it here and assume
+	     * that it will exist.
+	     */
+	    tickcount_offset += anow - tnow;
+#elif defined TIMING_SYNC_TICKCOUNT
+	    /*
+	     * If the tick count is more likely to be accurate, we
+	     * simply use that as our time value, which may mean we
+	     * run no timers in this call (because we got called
+	     * early), or alternatively it may mean we run lots of
+	     * timers in a hurry because we were called late.
+	     */
+	    anow = tnow;
+#else
+/*
+ * Any platform which defines TIMING_SYNC must also define one of the two
+ * auxiliary symbols TIMING_SYNC_ANOW and TIMING_SYNC_TICKCOUNT, to
+ * indicate which measurement to trust when the two disagree.
+ */
+#error TIMING_SYNC definition incomplete
+#endif
+	}
+    }
+#endif
+
+    now = anow;
+
+    while (1) {
+	first = (struct timer *)index234(timers, 0);
+
+	if (!first)
+	    return FALSE;	       /* no timers remaining */
+
+	if (find234(timer_contexts, first->ctx, NULL) == NULL) {
+	    /*
+	     * This timer belongs to a context that has been
+	     * expired. Delete it without running.
+	     */
+	    delpos234(timers, 0);
+	    sfree(first);
+	} else if (first->now - now <= 0) {
+	    /*
+	     * This timer is active and has reached its running
+	     * time. Run it.
+	     */
+	    delpos234(timers, 0);
+	    first->fn(first->ctx, first->now);
+	    sfree(first);
+	} else {
+	    /*
+	     * This is the first still-active timer that is in the
+	     * future. Return how long it has yet to go.
+	     */
+	    *next = first->now;
+	    return TRUE;
+	}
+    }
+}
+
+/*
+ * Call to expire all timers associated with a given context.
+ */
+void expire_timer_context(void *ctx)
+{
+    init_timers();
+
+    /*
+     * We don't bother to check the return value; if the context
+     * already wasn't in the tree (presumably because no timers
+     * ever actually got scheduled for it) then that's fine and we
+     * simply don't need to do anything.
+     */
+    del234(timer_contexts, ctx);
+}