Introduce a priority queue implementation.

This will be needed to keep track of multiple different deadlines
using a single timer.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>

makefile

@@ -25,9 +25,9 @@ LDLIBS	= -lm -lrt $(EXTRA_LDFLAGS)
 PRG	= ptp4l hwstamp_ctl nsm phc2sys phc_ctl pmc timemaster
 OBJ     = bmc.o clock.o clockadj.o clockcheck.o config.o e2e_tc.o fault.o \
  filter.o fsm.o hash.o linreg.o mave.o mmedian.o msg.o ntpshm.o nullf.o phc.o \
- pi.o port.o port_signaling.o print.o ptp4l.o p2p_tc.o raw.o rtnl.o servo.o \
- sk.o stats.o tc.o telecom.o tlv.o transport.o tsproc.o udp.o udp6.o uds.o \
- unicast_client.o unicast_fsm.o util.o version.o
+ pi.o port.o port_signaling.o pqueue.o print.o ptp4l.o p2p_tc.o raw.o rtnl.o \
+ servo.o sk.o stats.o tc.o telecom.o tlv.o transport.o tsproc.o udp.o udp6.o \
+ uds.o unicast_client.o unicast_fsm.o util.o version.o
 
 OBJECTS	= $(OBJ) hwstamp_ctl.o nsm.o phc2sys.o phc_ctl.o pmc.o pmc_common.o \
  sysoff.o timemaster.o

pqueue.c

@@ -0,0 +1,138 @@
+/**
+ * @file  pqueue.c
+ * @brief Implements a priority queue.
+ * @note  Copyright (c) 2015 Richard Cochran <richardcochran@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA.
+ */
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+#include "pqueue.h"
+
+#define parent(x)	(((1 + (x)) >> 1) - 1)
+#define left(x)		(((1 + (x)) << 1) - 1)
+#define right(x)	(((1 + (x)) << 1))
+
+struct pqueue {
+	int len;
+	int max;
+	int (*cmp)(void *a, void *b);
+	void **data;
+};
+
+static int pq_greater(struct pqueue *q, int a, int b)
+{
+	return q->cmp(q->data[a], q->data[b]) > 0 ? 1 : 0;
+}
+
+static void heapify(struct pqueue *q, int index)
+{
+	int i_max = index;
+	int left = left(index);
+	int right = right(index);
+
+	if (left < q->len) {
+		if (pq_greater(q, left, i_max))
+			i_max = left;
+	}
+
+	if (right < q->len && pq_greater(q, right, i_max)) {
+		i_max = right;
+	}
+
+	if (i_max != index) {
+		void *tmp = q->data[index];
+		q->data[index] = q->data[i_max];
+		q->data[i_max] = tmp;
+		heapify(q, i_max);
+	}
+}
+
+/* public methods */
+
+struct pqueue *pqueue_create(int max_length,
+			     int (*compare)(void *a, void *b))
+{
+	struct pqueue *q = calloc(1, sizeof(*q));
+	if (!q) {
+		return NULL;
+	}
+	q->len = 0;
+	q->max = max_length;
+	q->cmp = compare;
+	q->data = calloc(max_length, sizeof(void *));
+	if (!q->data) {
+		free(q);
+		return NULL;
+	}
+	return q;
+}
+
+void pqueue_destroy(struct pqueue *q)
+{
+	free(q->data);
+	free(q);
+}
+
+void *pqueue_extract(struct pqueue *q)
+{
+	void *data;
+
+	if (!q->len) {
+		return NULL;
+	}
+	data = q->data[0];
+	q->data[0] = q->data[q->len - 1];
+	q->len--;
+	heapify(q, 0);
+
+	return data;
+}
+
+int pqueue_insert(struct pqueue *q, void *d)
+{
+	int index;
+
+	if (q->len >= q->max) {
+		void **buf = realloc(q->data, 2 * q->max * sizeof(void *));
+		if (buf) {
+			q->data = buf;
+			q->max *= 2;
+		} else {
+			return -ENOMEM;
+		}
+	}
+	index = q->len;
+	q->len++;
+
+	while (index && (q->cmp(q->data[parent(index)], d) < 0)) {
+		q->data[index] = q->data[parent(index)];
+		index = parent(index);
+	}
+	q->data[index] = d;
+
+	return 0;
+}
+
+int pqueue_length(struct pqueue *q)
+{
+	return q->len;
+}
+
+void *pqueue_peek(struct pqueue *q)
+{
+	return q->len ? q->data[0] : (void *) 0;
+}

pqueue.h

@@ -0,0 +1,38 @@
+/**
+ * @file  pqueue.h
+ * @brief Implements a priority queue.
+ * @note  Copyright (c) 2015 Richard Cochran <richardcochran@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA.
+ */
+#ifndef HAVE_PQUEUE_H
+#define HAVE_PQUEUE_H
+
+struct pqueue;
+
+struct pqueue *pqueue_create(int max_length,
+			     int (*compare)(void *a, void *b));
+
+void pqueue_destroy(struct pqueue *q);
+
+void *pqueue_extract(struct pqueue *q);
+
+int pqueue_insert(struct pqueue *q, void *d);
+
+int pqueue_length(struct pqueue *q);
+
+void *pqueue_peek(struct pqueue *q);
+
+#endif