lqueue: Linked list queue implementation

This new module provides a simple queue implementation as a singly
linked (circular) list.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Makefile-ccan

@@ -68,6 +68,7 @@ MODS_WITH_SRC := antithread \
 	lbalance \
 	likely \
 	list \
+	lqueue \
 	md4 \
 	memmem \
 	net \

ccan/lqueue/LICENSE

@@ -0,0 +1 @@
+../../licenses/BSD-MIT

ccan/lqueue/_info

@@ -0,0 +1,57 @@
+#include "config.h"
+#include <stdio.h>
+#include <string.h>
+
+/**
+ * lqueue - Simple, singly-linked-list queue implementation
+ *
+ * This code provides a simple implementation of the Queue abstract
+ * data type in terms of a singly linked (circular) list.
+ *
+ * License: BSD-MIT
+ * Author: David Gibson <david@gibson.dropbear.id.au>
+ *
+ * Example:
+ *	#include <ccan/lqueue/lqueue.h>
+ *
+ *	struct arg {
+ *		const char *arg;
+ *		struct lqueue_link ql;
+ *	};
+ *
+ *	int main(int argc, char *argv[])
+ *	{
+ *		int i;
+ *		struct arg *a;
+ *		LQUEUE(argq);
+ *
+ *		for (i = 0; i < argc; i++) {
+ *			a = malloc(sizeof(*a));
+ *			a->arg = argv[i];
+ *			lqueue_enqueue(&argq, a, ql);
+ *		}
+ *
+ *		printf("Command line arguments in order:\n");
+ *
+ *		while (!lqueue_empty(&argq)) {
+ *			a = lqueue_dequeue(&argq, struct arg, ql);
+ *			printf("Argument: %s\n", a->arg);
+ *			free(a);
+ *		}
+ *
+ *		return 0;
+ *	}
+ */
+int main(int argc, char *argv[])
+{
+	/* Expect exactly one argument */
+	if (argc != 2)
+		return 1;
+
+	if (strcmp(argv[1], "depends") == 0) {
+		printf("ccan/container_of\n");
+		return 0;
+	}
+
+	return 1;
+}

ccan/lqueue/lqueue.h

@@ -0,0 +1,191 @@
+/* Licensed under BSD-MIT - see LICENSE file for details */
+#ifndef CCAN_LQUEUE_H
+#define CCAN_LQUEUE_H
+
+#include <stdbool.h>
+#include <stdio.h>
+#include <assert.h>
+
+#include <ccan/container_of/container_of.h>
+
+/**
+ * struct lqueue_link - a queue link
+ * @next: next entry, or front of queue, if this is the back
+ *
+ * This is used as a link within a queue entry.
+ *
+ * Example:
+ *	struct waiter {
+ *		char *name;
+ *		struct lqueue_link ql;
+ *	};
+ */
+struct lqueue_link {
+	struct lqueue_link *next;
+};
+
+/**
+ * struct lqueue - the head of a queue
+ * @b: the back of the queue (NULL if empty)
+ */
+struct lqueue {
+	struct lqueue_link *back;
+};
+
+/**
+ * LQUEUE - define and initialize an empty queue
+ * @name: the name of the lqueue.
+ *
+ * The LQUEUE macro defines an lqueue and initializes it to an empty
+ * queue.  It can be prepended by "static" to define a static lqueue.
+ *
+ * See also:
+ *	lqueue_init()
+ *
+ * Example:
+ *	LQUEUE(my_queue);
+ *
+ *	assert(lqueue_empty(&my_queue));
+ */
+#define LQUEUE(name) \
+	struct lqueue name = { NULL, }
+
+/**
+ * lqueue_init - initialize a queue
+ * @h: the lqueue to set to an empty queue
+ *
+ * Example:
+ *	struct lqueue *qp = malloc(sizeof(*qp));
+ *	lqueue_init(qp);
+ */
+static inline void lqueue_init(struct lqueue *q)
+{
+	q->back = NULL;
+}
+
+/**
+ * lqueue_empty - is a queue empty?
+ * @q: the queue
+ *
+ * If the queue is empty, returns true.
+ *
+ * Example:
+ *	assert(lqueue_empty(qp));
+ */
+static inline bool lqueue_empty(const struct lqueue *q)
+{
+	return (q->back == NULL);
+}
+
+/**
+ * lqueue_entry - convert an lqueue_link back into the structure containing it.
+ * @e: the lqueue_link
+ * @type: the type of the entry
+ * @member: the lqueue_link member of the type
+ *
+ * Example:
+ *	struct waiter {
+ *		char *name;
+ *		struct lqueue_link ql;
+ *	} w;
+ *	assert(lqueue_entry(&w.ql, struct waiter, ql) == &w);
+ */
+#define lqueue_entry(n, type, member) container_of_or_null(n, type, member)
+
+/**
+ * lqueue_front - get front entry in a queue
+ * @q: the queue
+ * @type: the type of queue entries
+ * @member: the lqueue_link entry
+ *
+ * If the queue is empty, returns NULL.
+ *
+ * Example:
+ *	struct waiter *f;
+ *
+ *	f = lqueue_front(qp, struct waiter, ql);
+ *	assert(lqueue_dequeue(qp, struct waiter, ql) == f);
+ */
+#define lqueue_front(q, type, member) \
+	lqueue_entry(lqueue_front_((q)), type, member)
+static inline struct lqueue_link *lqueue_front_(const struct lqueue *q)
+{
+	if (!q->back)
+		return NULL;
+	else
+		return q->back->next;
+}
+
+/**
+ * lqueue_back - get back entry in a queue
+ * @q: the queue
+ * @type: the type of queue entries
+ * @member: the lqueue_link entry
+ *
+ * If the queue is empty, returns NULL.
+ *
+ * Example:
+ *	struct waiter b;
+ *
+ *	lqueue_enqueue(qp, &b, ql);
+ *	assert(lqueue_back(qp, struct waiter, ql) == &b);
+ */
+#define lqueue_back(q, type, member) \
+	lqueue_entry(lqueue_back_((q)), type, member)
+static inline struct lqueue_link *lqueue_back_(const struct lqueue *q)
+{
+	return q->back;
+}
+
+/**
+ * lqueue_enqueue - add an entry to the back of a queue
+ * @q: the queue to add the node to
+ * @e: the item to enqueue
+ * @member: the lqueue_link field of *e
+ *
+ * The lqueue_link does not need to be initialized; it will be overwritten.
+ */
+#define lqueue_enqueue(q, e, member) \
+	lqueue_enqueue_((q), &((e)->member))
+static inline void lqueue_enqueue_(struct lqueue *q, struct lqueue_link *e)
+{
+	if (lqueue_empty(q)) {
+		/* New entry will be both front and back of queue */
+		e->next = e;
+		q->back = e;
+	} else {
+		e->next = lqueue_front_(q);
+		q->back->next = e;
+		q->back = e;
+	}
+}
+
+/**
+ * lqueue_dequeue - remove and return the entry from the front of the queue
+ * @q: the queue
+ * @type: the type of queue entries
+ * @member: the lqueue_link field of @type
+ *
+ * Note that this leaves the returned entry's link in an undefined
+ * state; it can be added to another queue, but not deleted again.
+ */
+#define lqueue_dequeue(q, type, member) \
+	lqueue_entry(lqueue_dequeue_((q)), type, member)
+static inline struct lqueue_link *lqueue_dequeue_(struct lqueue *q)
+{
+	struct lqueue_link *front;
+
+	if (lqueue_empty(q))
+		return NULL;
+
+	front = lqueue_front_(q);
+	if (front == lqueue_back_(q)) {
+		assert(front->next == front);
+		q->back = NULL;
+	} else {
+		q->back->next = front->next;
+	}
+	return front;
+}
+
+#endif /* CCAN_LQUEUE_H */

ccan/lqueue/test/run.c

@@ -0,0 +1,69 @@
+#include "config.h"
+
+#include <ccan/lqueue/lqueue.h>
+#include <ccan/tap/tap.h>
+
+struct waiter {
+	const char *name;
+	struct lqueue_link ql;
+};
+
+int main(void)
+{
+	LQUEUE(q);
+	struct waiter a = { "Alice" };
+	struct waiter b = { "Bob" };
+	struct waiter c = { "Carol" };
+	struct waiter *waiter;
+
+	/* This is how many tests you plan to run */
+	plan_tests(25);
+
+	ok1(lqueue_empty(&q));
+	ok1(lqueue_front(&q, struct waiter, ql) == NULL);
+	ok1(lqueue_back(&q, struct waiter, ql) == NULL);
+
+	lqueue_enqueue(&q, &a, ql);
+
+	ok1(!lqueue_empty(&q));
+	ok1(lqueue_front(&q, struct waiter, ql) == &a);
+	ok1(lqueue_back(&q, struct waiter, ql) == &a);
+
+	lqueue_enqueue(&q, &b, ql);
+
+	ok1(!lqueue_empty(&q));
+	ok1(lqueue_front(&q, struct waiter, ql) == &a);
+	ok1(lqueue_back(&q, struct waiter, ql) == &b);
+
+	lqueue_enqueue(&q, &c, ql);
+
+	ok1(!lqueue_empty(&q));
+	ok1(lqueue_front(&q, struct waiter, ql) == &a);
+	ok1(lqueue_back(&q, struct waiter, ql) == &c);
+
+	waiter = lqueue_dequeue(&q, struct waiter, ql);
+	ok1(waiter == &a);
+
+	ok1(!lqueue_empty(&q));
+	ok1(lqueue_front(&q, struct waiter, ql) == &b);
+	ok1(lqueue_back(&q, struct waiter, ql) == &c);
+
+	waiter = lqueue_dequeue(&q, struct waiter, ql);
+	ok1(waiter == &b);
+
+	ok1(!lqueue_empty(&q));
+	ok1(lqueue_front(&q, struct waiter, ql) == &c);
+	ok1(lqueue_back(&q, struct waiter, ql) == &c);
+
+	waiter = lqueue_dequeue(&q, struct waiter, ql);
+	ok1(waiter == &c);
+
+	ok1(lqueue_empty(&q));
+	ok1(lqueue_front(&q, struct waiter, ql) == NULL);
+	ok1(lqueue_back(&q, struct waiter, ql) == NULL);
+
+	ok1(lqueue_dequeue(&q, struct waiter, ql) == NULL);
+
+	/* This exits depending on whether all tests passed */
+	return exit_status();
+}