adding zephyr-im master branch

server/timer.c

@@ -0,0 +1,250 @@
+/* This file is part of the Project Athena Zephyr Notification System.
+ * It contains functions for managing multiple timeouts.
+ *
+ *      Created by:     John T. Kohl
+ *      Derived from timer_manager_ by Ken Raeburn
+ *
+ *      $Id$
+ *
+ */
+
+#include "zserver.h"
+
+#ifndef SABER
+#ifndef lint
+static const char rcsid[] =
+"$Id$";
+#endif /* lint */
+#endif /* SABER */
+
+/*
+ * timer_manager_ -- routines for handling timers in login_shell
+ * (and elsewhere)
+ *
+ * Copyright 1986 Student Information Processing Board,
+ * Massachusetts Institute of Technology
+ *
+ * written by Ken Raeburn
+ 
+ Permission to use, copy, modify, and distribute this
+ software and its documentation for any purpose and without
+ fee is hereby granted, provided that the above copyright
+ notice appear in all copies and that both that copyright
+ notice and this permission notice appear in supporting
+ documentation, and that the name of M.I.T. and the Student
+ Information Processing Board not be used in
+ advertising or publicity pertaining to distribution of the
+ software without specific, written prior permission.
+ M.I.T. and the Student Information Processing Board
+ make no representations about the suitability of
+ this software for any purpose.  It is provided "as is"
+ without express or implied warranty.
+ 
+ */
+
+
+/*
+ * External functions:
+ *
+ * Timer *timer_set_rel (time_rel, proc, arg)
+ *      long time_rel;
+ *      void (*proc)();
+ *      void *arg;
+ * Timer *timer_set_abs (time_abs, proc, arg)
+ *      long time_abs;
+ *      void (*proc)();
+ *      void *arg;
+ *
+ * void timer_reset(tmr)
+ *      Timer *tmr;
+ *
+ * void timer_process()
+ *
+ */
+
+/* DELTA is just an offset to keep the size a bit less than a power 
+ * of two.  It's measured in pointers, so it's 32 bytes on most
+ * systems. */
+#define DELTA 8
+#define INITIAL_HEAP_SIZE (1024 - DELTA)
+
+/* We have three operations which we need to be able to perform
+ * quickly: adding a timer, deleting a timer given a pointer to
+ * it, and determining which timer will be the next to go off.  A
+ * heap is an ideal data structure for these purposes, so we use
+ * one.  The heap is an array of pointers to timers, and each timer
+ * knows the position of its pointer in the heap.
+ *
+ * Okay, what is the heap, exactly?  It's a data structure,
+ * represented as an array, with the invariant condition that
+ * the timeout of heap[i] is less than or equal to the timeout of
+ * heap[i * 2 + 1] and heap[i * 2 + 2] (assuming i * 2 + 1 and
+ * i * 2 + 2 are valid * indices).  An obvious consequence of this
+ * is that heap[0] has the lowest timer value, so finding the first
+ * timer to go off is easy.  We say that an index i has "children"
+ * i * 2 + 1 and i * 2 + 1, and the "parent" (i - 1) / 2.
+ *
+ * To add a timer to the heap, we start by adding it to the end, and
+ * then keep swapping it with its parent until it has a parent with
+ * a timer value less than its value.  With a little bit of thought,
+ * you can see that this preserves the heap property on all indices
+ * of the array.
+ *
+ * To delete a timer at position i from the heap, we discard it and
+ * fill in its position with the last timer in the heap.  In order
+ * to restore the heap, we have to consider two cases: the timer
+ * value at i is less than that of its parent, or the timer value at
+ * i is greater than that of one of its children.  In the first case,
+ * we propagate the timer at i up the tree, swapping it with its
+ * parent, until the heap is restored; in the second case, we
+ * propagate the timer down the tree, swapping it with its least
+ * child, until the heap is restored. */
+
+/* In order to ensure that the back pointers from timers are consistent
+ * with the heap pointers, all heap assignments should be done with the
+ * HEAP_ASSIGN() macro, which sets the back pointer and updates the
+ * heap at the same time. */
+#define PARENT(i) (((i) - 1) / 2)
+#define CHILD1(i) ((i) * 2 + 1)
+#define CHILD2(i) ((i) * 2 + 2)
+#define TIME(i) (heap[i]->abstime)
+#define HEAP_ASSIGN(pos, tmr) ((heap[pos] = (tmr))->heap_pos = (pos))
+
+static Timer **heap;
+static int num_timers = 0;
+static int heap_size = 0;
+
+static void timer_botch (void*);
+static Timer *add_timer (Timer *);
+
+Timer *
+timer_set_rel(long time_rel,
+	      void (*proc)(void *),
+	      void *arg)
+{
+    Timer *new_t;
+
+    new_t = (Timer *) malloc(sizeof(*new_t));
+    if (new_t == NULL)
+	return(NULL);
+    new_t->abstime = time_rel + NOW;
+    new_t->func = proc;
+    new_t->arg = arg;
+    return add_timer(new_t);
+}
+
+void
+timer_reset(Timer *tmr)
+{
+    int pos, min;
+
+    /* Free the timer, saving its heap position. */
+    pos = tmr->heap_pos;
+    free(tmr);
+
+    if (pos != num_timers - 1) {
+	/* Replace the timer with the last timer in the heap and
+	 * restore the heap, propagating the timer either up or
+	 * down, depending on which way it violates the heap
+	 * property to insert the last timer in place of the
+	 * deleted timer. */
+	if (pos > 0 && TIME(num_timers - 1) < TIME(PARENT(pos))) {
+	    do {
+		HEAP_ASSIGN(pos, heap[PARENT(pos)]);
+		pos = PARENT(pos);
+	    } while (pos > 0 && TIME(num_timers - 1) < TIME(PARENT(pos)));
+	    HEAP_ASSIGN(pos, heap[num_timers - 1]);
+	} else {
+	    while (CHILD2(pos) < num_timers) {
+		min = num_timers - 1;
+		if (TIME(CHILD1(pos)) < TIME(min))
+		    min = CHILD1(pos);
+		if (TIME(CHILD2(pos)) < TIME(min))
+		    min = CHILD2(pos);
+		HEAP_ASSIGN(pos, heap[min]);
+		pos = min;
+	    }
+	    if (pos != num_timers - 1)
+		HEAP_ASSIGN(pos, heap[num_timers - 1]);
+	}
+    }
+    num_timers--;
+}
+
+
+#define set_timeval(t,s) ((t).tv_sec=(s),(t).tv_usec=0,(t))
+
+static Timer *
+add_timer(Timer *new)
+{
+    int pos;
+
+    /* Create or resize the heap as necessary. */
+    if (heap_size == 0) {
+	heap_size = INITIAL_HEAP_SIZE;
+	heap = (Timer **) malloc(heap_size * sizeof(Timer *));
+    } else if (num_timers >= heap_size) {
+	heap_size = heap_size * 2 + DELTA;
+	heap = (Timer **) realloc(heap, heap_size * sizeof(Timer *));
+    }
+    if (!heap) {
+	free(new);
+	return NULL;
+    }
+
+    /* Insert the Timer *into the heap. */
+    pos = num_timers;
+    while (pos > 0 && new->abstime < TIME(PARENT(pos))) {
+	HEAP_ASSIGN(pos, heap[PARENT(pos)]);
+	pos = PARENT(pos);
+    }
+    HEAP_ASSIGN(pos, new);
+    num_timers++;
+
+    return new;
+}
+
+void
+timer_process(void)
+{
+    Timer *t;
+    timer_proc func;
+    void *arg;
+
+    if (num_timers == 0 || heap[0]->abstime > NOW)
+	return;
+
+    /* Remove the first timer from the heap, remembering its
+     * function and argument. */
+    t = heap[0];
+    func = t->func;
+    arg = t->arg;
+    t->func = timer_botch;
+    t->arg = NULL;
+    timer_reset(t);
+	
+    /* Run the function. */
+    func(arg);
+}
+
+struct timeval *
+timer_timeout(struct timeval *tvbuf)
+{
+    if (num_timers > 0) {
+	tvbuf->tv_sec = heap[0]->abstime - NOW;
+	if (tvbuf->tv_sec < 0)
+	    tvbuf->tv_sec = 0;
+	tvbuf->tv_usec = 0;
+	return tvbuf;
+    } else {
+	return NULL;
+    }
+}
+
+static void
+timer_botch(void *arg)
+{
+    syslog(LOG_CRIT, "timer botch\n");
+    abort();
+}
+