--- /dev/null
+/* GNU LGPL version 2 (or later) - see LICENSE file for details */
+#ifndef CCAN_LPQ_H
+#define CCAN_LPQ_H
+
+#include <stdbool.h>
+
+#include <ccan/cast/cast.h>
+#include <ccan/tcon/tcon.h>
+#include <ccan/order/order.h>
+
+/**
+ * struct lpq_link - a priority link
+ * @next: next entry in the list of items in the priority queue
+ *
+ * This is used as a link within a priority queue entry.
+ *
+ * Example:
+ * struct waiter {
+ * char *name;
+ * int priority;
+ * struct lpq_link pql;
+ * };
+ */
+struct lpq_link {
+ struct lpq_link *next;
+};
+
+/**
+ * struct lpq_ - a linear priority queue (internal type)
+ * @order: ordering callback to compare entry priorities
+ * @list: head of the list of items in the priority queue
+ */
+struct lpq_ {
+ struct _total_order order;
+ struct lpq_link *list;
+};
+
+/**
+ * LPQ - define and initialize an empty priority queue
+ * @type: type of items in the queue / items compared by the callback
+ * @link: name of the lpq_link field in @type
+ *
+ * The LPQ macro defines an lpq and initializes it to an empty
+ * priority queue. It can be prepended by "static" to define a static
+ * lpq.
+ *
+ * See also:
+ * lpq_init()
+ */
+#define LPQ(etype_, link_) \
+ TCON_WRAP(struct lpq_, \
+ TCON_CONTAINER(canary, etype_, link_))
+
+/**
+ * lpq_init - initialize a priority queue
+ * @pq: the lpq to set to an empty queue
+ * @order: priority ordering callback for items in the queue
+ *
+ * Example:
+ * total_order_by_field(my_order, int, struct waiter, priority);
+ * LPQ(struct waiter, pql) *pqp = malloc(sizeof(*pqp));
+ * lpq_init(pqp, my_order.cb, my_order.ctx);
+ */
+#define lpq_init(pq_, order_cb_, order_ctx_) \
+ lpq_init_(tcon_unwrap(pq_), \
+ total_order_cast((order_cb_), \
+ tcon_container_type((pq_), canary), \
+ (order_ctx_)), \
+ (order_ctx_))
+static inline void lpq_init_(struct lpq_ *pq,
+ _total_order_cb order_cb, void *order_ctx)
+{
+ pq->order.cb = order_cb;
+ pq->order.ctx = order_ctx;
+ pq->list = NULL;
+}
+
+/**
+ * lpq_empty - is a priority queue empty?
+ * @pq: the priority queue
+ *
+ * If the priority queue is empty, returns true.
+ */
+#define lpq_empty(pq_) \
+ lpq_empty_(tcon_unwrap(pq_))
+static inline bool lpq_empty_(const struct lpq_ *pq)
+{
+ return (pq->list == NULL);
+}
+
+/**
+ * lpq_entry - convert an lpq_link back into the structure containing it.
+ * @pq: the priority queue
+ * @l: the lpq_link
+ */
+#define lpq_entry(pq_, l_) tcon_container_of((pq_), canary, (l_))
+
+/**
+ * lpq_frontp_ - get pointer to pointer to front element (internal function)
+ */
+struct lpq_link **lpq_frontp_(struct lpq_ *pq, size_t offset);
+
+/**
+ * lpq_front - get front (highest priority) entry in a priority queue
+ * @pq: the priority queue
+ *
+ * If the priority queue is empty, returns NULL.
+ *
+ * Example:
+ * struct waiter *f;
+ *
+ * f = lpq_front(pqp);
+ * assert(lpq_dequeue(pqp) == f);
+ */
+#define lpq_front(pq_) \
+ lpq_entry((pq_), lpq_front_(tcon_unwrap(pq_), \
+ tcon_offset((pq_), canary)))
+static inline struct lpq_link *lpq_front_(const struct lpq_ *pq, size_t offset)
+{
+ struct lpq_link **frontp = lpq_frontp_(cast_const(struct lpq_ *, pq),
+ offset);
+
+ return frontp ? *frontp : NULL;
+}
+
+/**
+ * lpq_enqueue - add an entry to a priority queue
+ * @pq: the priority queue to add the node to
+ * @e: the item to enqueue
+ *
+ * The lpq_link does not need to be initialized; it will be overwritten.
+ */
+#define lpq_enqueue(pq_, e_) \
+ lpq_enqueue_(tcon_unwrap(pq_), tcon_member_of((pq_), canary, (e_)))
+static inline void lpq_enqueue_(struct lpq_ *pq, struct lpq_link *e)
+{
+ e->next = pq->list;
+ pq->list = e;
+}
+
+/**
+ * lpq_dequeue - remove and return the highest priority item from the
+ * priority queue
+ * @pq: the priority queue
+ *
+ * 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 lpq_dequeue(pq_) \
+ lpq_entry((pq_), lpq_dequeue_(tcon_unwrap(pq_), \
+ tcon_offset((pq_), canary)))
+static inline struct lpq_link *lpq_dequeue_(struct lpq_ *pq, size_t offset)
+{
+ struct lpq_link **frontp = lpq_frontp_(pq, offset);
+ struct lpq_link *front;
+
+ if (!frontp)
+ return NULL;
+
+ front = *frontp;
+ *frontp = front->next;
+ return front;
+}
+
+/**
+ * lpq_reorder - adjust the queue after an element changes priority
+ * @pq: the priority queue
+ * @e: the entry which has changed priority
+ *
+ * If any element already inserted into @pq is altered to change its
+ * priority, lpq_reorder() must be called before any other function is
+ * called on @pq.
+ *
+ * NOTE: For the dumb priority queue implementation in lpq, this is
+ * actually a no-op. But this call exists so that users will be more
+ * easily able to change to a better priority queue implementation
+ * later.
+ */
+#define lpq_reorder(pq_, e_) \
+ (lpq_reorder_(tcon_unwrap(pq_), tcon_member_of((pq_), canary, (e_))))
+static inline void lpq_reorder_(struct lpq_ *pq, struct lpq_link *e)
+{
+}
+
+#endif /* CCAN_LPQ_H */
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