39934deb |
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. |
c2eb6cb7 |
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 | * |
39934deb |
28 | */ |
29 | |
30 | #include <assert.h> |
31 | #include <stdio.h> |
32 | |
33 | #include "putty.h" |
34 | #include "tree234.h" |
35 | |
36 | struct timer { |
37 | timer_fn_t fn; |
38 | void *ctx; |
39 | long now; |
c2eb6cb7 |
40 | long when_set; |
39934deb |
41 | }; |
42 | |
43 | static tree234 *timers = NULL; |
1605c493 |
44 | static tree234 *timer_contexts = NULL; |
39934deb |
45 | static long now = 0L; |
46 | |
47 | static 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 | */ |
8136216b |
63 | #ifdef __LCC__ |
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 < 0) |
68 | return -1; |
69 | else if (c > 0) |
70 | return +1; |
71 | } |
72 | #else |
39934deb |
73 | if (a->fn < b->fn) |
74 | return -1; |
75 | else if (a->fn > b->fn) |
76 | return +1; |
8136216b |
77 | #endif |
39934deb |
78 | |
79 | if (a->ctx < b->ctx) |
80 | return -1; |
81 | else if (a->ctx > b->ctx) |
82 | return +1; |
83 | |
84 | /* |
85 | * Failing _that_, the two entries genuinely are equal, and we |
86 | * never have a need to store them separately in the tree. |
87 | */ |
88 | return 0; |
89 | } |
90 | |
91 | static int compare_timer_contexts(void *av, void *bv) |
92 | { |
1605c493 |
93 | char *a = (char *)av; |
94 | char *b = (char *)bv; |
39934deb |
95 | if (a < b) |
96 | return -1; |
97 | else if (a > b) |
98 | return +1; |
99 | return 0; |
100 | } |
101 | |
102 | static void init_timers(void) |
103 | { |
104 | if (!timers) { |
105 | timers = newtree234(compare_timers); |
1605c493 |
106 | timer_contexts = newtree234(compare_timer_contexts); |
39934deb |
107 | now = GETTICKCOUNT(); |
108 | } |
109 | } |
110 | |
111 | long schedule_timer(int ticks, timer_fn_t fn, void *ctx) |
112 | { |
113 | long when; |
114 | struct timer *t, *first; |
115 | |
116 | init_timers(); |
117 | |
c2eb6cb7 |
118 | now = GETTICKCOUNT(); |
119 | when = ticks + now; |
2ac3322e |
120 | |
121 | /* |
122 | * Just in case our various defences against timing skew fail |
123 | * us: if we try to schedule a timer that's already in the |
124 | * past, we instead schedule it for the immediate future. |
125 | */ |
126 | if (when - now <= 0) |
127 | when = now + 1; |
39934deb |
128 | |
129 | t = snew(struct timer); |
130 | t->fn = fn; |
131 | t->ctx = ctx; |
132 | t->now = when; |
c2eb6cb7 |
133 | t->when_set = now; |
39934deb |
134 | |
135 | if (t != add234(timers, t)) { |
136 | sfree(t); /* identical timer already exists */ |
1605c493 |
137 | } else { |
138 | add234(timer_contexts, t->ctx);/* don't care if this fails */ |
39934deb |
139 | } |
140 | |
141 | first = (struct timer *)index234(timers, 0); |
142 | if (first == t) { |
143 | /* |
144 | * This timer is the very first on the list, so we must |
145 | * notify the front end. |
146 | */ |
147 | timer_change_notify(first->now); |
148 | } |
149 | |
150 | return when; |
151 | } |
152 | |
153 | /* |
154 | * Call to run any timers whose time has reached the present. |
155 | * Returns the time (in ticks) expected until the next timer after |
156 | * that triggers. |
157 | */ |
158 | int run_timers(long anow, long *next) |
159 | { |
160 | struct timer *first; |
161 | |
162 | init_timers(); |
163 | |
c2eb6cb7 |
164 | now = GETTICKCOUNT(); |
39934deb |
165 | |
166 | while (1) { |
167 | first = (struct timer *)index234(timers, 0); |
168 | |
169 | if (!first) |
170 | return FALSE; /* no timers remaining */ |
171 | |
1605c493 |
172 | if (find234(timer_contexts, first->ctx, NULL) == NULL) { |
173 | /* |
174 | * This timer belongs to a context that has been |
175 | * expired. Delete it without running. |
176 | */ |
177 | delpos234(timers, 0); |
178 | sfree(first); |
c2eb6cb7 |
179 | } else if (first->now - now <= 0 || |
180 | now - (first->when_set - 10) < 0) { |
39934deb |
181 | /* |
182 | * This timer is active and has reached its running |
183 | * time. Run it. |
184 | */ |
185 | delpos234(timers, 0); |
186 | first->fn(first->ctx, first->now); |
187 | sfree(first); |
188 | } else { |
189 | /* |
190 | * This is the first still-active timer that is in the |
191 | * future. Return how long it has yet to go. |
192 | */ |
193 | *next = first->now; |
194 | return TRUE; |
195 | } |
196 | } |
197 | } |
198 | |
199 | /* |
200 | * Call to expire all timers associated with a given context. |
201 | */ |
202 | void expire_timer_context(void *ctx) |
203 | { |
1605c493 |
204 | init_timers(); |
5e376138 |
205 | |
1605c493 |
206 | /* |
207 | * We don't bother to check the return value; if the context |
208 | * already wasn't in the tree (presumably because no timers |
209 | * ever actually got scheduled for it) then that's fine and we |
210 | * simply don't need to do anything. |
211 | */ |
212 | del234(timer_contexts, ctx); |
39934deb |
213 | } |