1 /* This file is part of the Project Athena Zephyr Notification System.
2 * It contains functions for managing multiple timeouts.
4 * Created by: John T. Kohl
5 * Derived from timer_manager_ by Ken Raeburn
16 static const char rcsid[] =
22 * timer_manager_ -- routines for handling timers in login_shell
25 * Copyright 1986 Student Information Processing Board,
26 * Massachusetts Institute of Technology
28 * written by Ken Raeburn
30 Permission to use, copy, modify, and distribute this
31 software and its documentation for any purpose and without
32 fee is hereby granted, provided that the above copyright
33 notice appear in all copies and that both that copyright
34 notice and this permission notice appear in supporting
35 documentation, and that the name of M.I.T. and the Student
36 Information Processing Board not be used in
37 advertising or publicity pertaining to distribution of the
38 software without specific, written prior permission.
39 M.I.T. and the Student Information Processing Board
40 make no representations about the suitability of
41 this software for any purpose. It is provided "as is"
42 without express or implied warranty.
50 * Timer *timer_set_rel (time_rel, proc, arg)
54 * Timer *timer_set_abs (time_abs, proc, arg)
59 * void timer_reset(tmr)
62 * void timer_process()
66 /* DELTA is just an offset to keep the size a bit less than a power
67 * of two. It's measured in pointers, so it's 32 bytes on most
70 #define INITIAL_HEAP_SIZE (1024 - DELTA)
72 /* We have three operations which we need to be able to perform
73 * quickly: adding a timer, deleting a timer given a pointer to
74 * it, and determining which timer will be the next to go off. A
75 * heap is an ideal data structure for these purposes, so we use
76 * one. The heap is an array of pointers to timers, and each timer
77 * knows the position of its pointer in the heap.
79 * Okay, what is the heap, exactly? It's a data structure,
80 * represented as an array, with the invariant condition that
81 * the timeout of heap[i] is less than or equal to the timeout of
82 * heap[i * 2 + 1] and heap[i * 2 + 2] (assuming i * 2 + 1 and
83 * i * 2 + 2 are valid * indices). An obvious consequence of this
84 * is that heap[0] has the lowest timer value, so finding the first
85 * timer to go off is easy. We say that an index i has "children"
86 * i * 2 + 1 and i * 2 + 1, and the "parent" (i - 1) / 2.
88 * To add a timer to the heap, we start by adding it to the end, and
89 * then keep swapping it with its parent until it has a parent with
90 * a timer value less than its value. With a little bit of thought,
91 * you can see that this preserves the heap property on all indices
94 * To delete a timer at position i from the heap, we discard it and
95 * fill in its position with the last timer in the heap. In order
96 * to restore the heap, we have to consider two cases: the timer
97 * value at i is less than that of its parent, or the timer value at
98 * i is greater than that of one of its children. In the first case,
99 * we propagate the timer at i up the tree, swapping it with its
100 * parent, until the heap is restored; in the second case, we
101 * propagate the timer down the tree, swapping it with its least
102 * child, until the heap is restored. */
104 /* In order to ensure that the back pointers from timers are consistent
105 * with the heap pointers, all heap assignments should be done with the
106 * HEAP_ASSIGN() macro, which sets the back pointer and updates the
107 * heap at the same time. */
108 #define PARENT(i) (((i) - 1) / 2)
109 #define CHILD1(i) ((i) * 2 + 1)
110 #define CHILD2(i) ((i) * 2 + 2)
111 #define TIME(i) (heap[i]->abstime)
112 #define HEAP_ASSIGN(pos, tmr) ((heap[pos] = (tmr))->heap_pos = (pos))
115 static int num_timers = 0;
116 static int heap_size = 0;
118 static void timer_botch (void*);
119 static Timer *add_timer (Timer *);
122 timer_set_rel(long time_rel,
123 void (*proc)(void *),
128 new_t = (Timer *) malloc(sizeof(*new_t));
131 new_t->abstime = time_rel + time(NULL);
134 return add_timer(new_t);
138 timer_reset(Timer *tmr)
142 /* Free the timer, saving its heap position. */
146 if (pos != num_timers - 1) {
147 /* Replace the timer with the last timer in the heap and
148 * restore the heap, propagating the timer either up or
149 * down, depending on which way it violates the heap
150 * property to insert the last timer in place of the
152 if (pos > 0 && TIME(num_timers - 1) < TIME(PARENT(pos))) {
154 HEAP_ASSIGN(pos, heap[PARENT(pos)]);
156 } while (pos > 0 && TIME(num_timers - 1) < TIME(PARENT(pos)));
157 HEAP_ASSIGN(pos, heap[num_timers - 1]);
159 while (CHILD2(pos) < num_timers) {
160 min = num_timers - 1;
161 if (TIME(CHILD1(pos)) < TIME(min))
163 if (TIME(CHILD2(pos)) < TIME(min))
165 HEAP_ASSIGN(pos, heap[min]);
168 if (pos != num_timers - 1)
169 HEAP_ASSIGN(pos, heap[num_timers - 1]);
176 #define set_timeval(t,s) ((t).tv_sec=(s),(t).tv_usec=0,(t))
179 add_timer(Timer *new)
183 /* Create or resize the heap as necessary. */
184 if (heap_size == 0) {
185 heap_size = INITIAL_HEAP_SIZE;
186 heap = (Timer **) malloc(heap_size * sizeof(Timer *));
187 } else if (num_timers >= heap_size) {
188 heap_size = heap_size * 2 + DELTA;
189 heap = (Timer **) realloc(heap, heap_size * sizeof(Timer *));
196 /* Insert the Timer *into the heap. */
198 while (pos > 0 && new->abstime < TIME(PARENT(pos))) {
199 HEAP_ASSIGN(pos, heap[PARENT(pos)]);
202 HEAP_ASSIGN(pos, new);
215 if (num_timers == 0 || heap[0]->abstime > time(NULL))
218 /* Remove the first timer from the heap, remembering its
219 * function and argument. */
223 t->func = timer_botch;
227 /* Run the function. */
232 timer_timeout(struct timeval *tvbuf)
234 if (num_timers > 0) {
235 tvbuf->tv_sec = heap[0]->abstime - time(NULL);
236 if (tvbuf->tv_sec < 0)
246 timer_botch(void *arg)
248 syslog(LOG_CRIT, "timer botch\n");