source: filezilla/trunk/fuentes/src/putty/timing.c @ 130

Last change on this file since 130 was 130, checked in by jrpelegrina, 4 years ago

First release to xenial

File size: 5.3 KB
Line 
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 * The problem is that computer clocks aren't perfectly accurate.
13 * The GETTICKCOUNT function returns a 32bit number that normally
14 * increases by about 1000 every second. On windows this uses the PC's
15 * interrupt timer and so is only accurate to around 20ppm.  On unix it's
16 * a value that's calculated from the current UTC time and so is in theory
17 * accurate in the long term but may jitter and jump in the short term.
18 *
19 * What PuTTY needs from these timers is simply a way of delaying the
20 * calling of a function for a little while, if it's occasionally called a
21 * little early or late that's not a problem. So to protect against clock
22 * jumps schedule_timer records the time that it was called in the timer
23 * structure. With this information the run_timers function can see when
24 * the current GETTICKCOUNT value is after the time the event should be
25 * fired OR before the time it was set. In the latter case the clock must
26 * have jumped, the former is (probably) just the normal passage of time.
27 *
28 */
29
30#include <assert.h>
31#include <stdio.h>
32
33#include "putty.h"
34#include "tree234.h"
35
36struct timer {
37    timer_fn_t fn;
38    void *ctx;
39    unsigned long now;
40    unsigned long when_set;
41};
42
43static tree234 *timers = NULL;
44static tree234 *timer_contexts = NULL;
45static unsigned long now = 0L;
46
47static int compare_timers(void *av, void *bv)
48{
49    struct timer *a = (struct timer *)av;
50    struct timer *b = (struct timer *)bv;
51    long at = a->now - now;
52    long bt = b->now - now;
53
54    if (at < bt)
55        return -1;
56    else if (at > bt)
57        return +1;
58
59    /*
60     * Failing that, compare on the other two fields, just so that
61     * we don't get unwanted equality.
62     */
63#if defined(__LCC__) || defined(__clang__)
64    /* lcc won't let us compare function pointers. Legal, but annoying. */
65    {
66        int c = memcmp(&a->fn, &b->fn, sizeof(a->fn));
67        if (c)
68            return c;
69    }
70#else   
71    if (a->fn < b->fn)
72        return -1;
73    else if (a->fn > b->fn)
74        return +1;
75#endif
76
77    if (a->ctx < b->ctx)
78        return -1;
79    else if (a->ctx > b->ctx)
80        return +1;
81
82    /*
83     * Failing _that_, the two entries genuinely are equal, and we
84     * never have a need to store them separately in the tree.
85     */
86    return 0;
87}
88
89static int compare_timer_contexts(void *av, void *bv)
90{
91    char *a = (char *)av;
92    char *b = (char *)bv;
93    if (a < b)
94        return -1;
95    else if (a > b)
96        return +1;
97    return 0;
98}
99
100static void init_timers(void)
101{
102    if (!timers) {
103        timers = newtree234(compare_timers);
104        timer_contexts = newtree234(compare_timer_contexts);
105        now = GETTICKCOUNT();
106    }
107}
108
109unsigned long schedule_timer(int ticks, timer_fn_t fn, void *ctx)
110{
111    unsigned long when;
112    struct timer *t, *first;
113
114    init_timers();
115
116    now = GETTICKCOUNT();
117    when = ticks + now;
118
119    /*
120     * Just in case our various defences against timing skew fail
121     * us: if we try to schedule a timer that's already in the
122     * past, we instead schedule it for the immediate future.
123     */
124    if (when - now <= 0)
125        when = now + 1;
126
127    t = snew(struct timer);
128    t->fn = fn;
129    t->ctx = ctx;
130    t->now = when;
131    t->when_set = now;
132
133    if (t != add234(timers, t)) {
134        sfree(t);                      /* identical timer already exists */
135    } else {
136        add234(timer_contexts, t->ctx);/* don't care if this fails */
137    }
138
139    first = (struct timer *)index234(timers, 0);
140    if (first == t) {
141        /*
142         * This timer is the very first on the list, so we must
143         * notify the front end.
144         */
145        timer_change_notify(first->now);
146    }
147
148    return when;
149}
150
151/*
152 * Call to run any timers whose time has reached the present.
153 * Returns the time (in ticks) expected until the next timer after
154 * that triggers.
155 */
156int run_timers(unsigned long anow, unsigned long *next)
157{
158    struct timer *first;
159
160    init_timers();
161
162    now = GETTICKCOUNT();
163
164    while (1) {
165        first = (struct timer *)index234(timers, 0);
166
167        if (!first)
168            return FALSE;              /* no timers remaining */
169
170        if (find234(timer_contexts, first->ctx, NULL) == NULL) {
171            /*
172             * This timer belongs to a context that has been
173             * expired. Delete it without running.
174             */
175            delpos234(timers, 0);
176            sfree(first);
177        } else if (now - (first->when_set - 10) >
178                   first->now - (first->when_set - 10)) {
179            /*
180             * This timer is active and has reached its running
181             * time. Run it.
182             */
183            delpos234(timers, 0);
184            first->fn(first->ctx, first->now);
185            sfree(first);
186        } else {
187            /*
188             * This is the first still-active timer that is in the
189             * future. Return how long it has yet to go.
190             */
191            *next = first->now;
192            return TRUE;
193        }
194    }
195}
196
197/*
198 * Call to expire all timers associated with a given context.
199 */
200void expire_timer_context(void *ctx)
201{
202    init_timers();
203
204    /*
205     * We don't bother to check the return value; if the context
206     * already wasn't in the tree (presumably because no timers
207     * ever actually got scheduled for it) then that's fine and we
208     * simply don't need to do anything.
209     */
210    del234(timer_contexts, ctx);
211}
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