--- /dev/null
+#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;
+}
--- /dev/null
+/* 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 */
--- /dev/null
+#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();
+}
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