lqueue: Linked list queue implementation

[ccan] / ccan / lqueue / lqueue.h

diff --git a/ccan/lqueue/lqueue.h b/ccan/lqueue/lqueue.h
new file mode 100644 (file)
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--- /dev/null
+++ b/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 */