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/* A FIFO queue with constant-time enqueue and dequeue operations.
Copyright (C) 2014 Free Software Foundation, Inc.
Written by Justus Winter <4winter@informatik.uni-hamburg.de>
This file is part of the GNU Hurd.
The GNU Hurd 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, or (at
your option) any later version.
The GNU Hurd 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 the GNU Hurd. If not, see <http://www.gnu.org/licenses/>. */
#include <stdbool.h>
/* A FIFO queue with constant-time enqueue and dequeue operations. */
struct item {
struct item *next;
};
struct queue {
struct item *head;
struct item **tail;
};
static inline void
queue_init (struct queue *q)
{
q->head = NULL;
q->tail = &q->head;
}
static inline void
queue_enqueue (struct queue *q, struct item *r)
{
*q->tail = r;
q->tail = &r->next;
r->next = NULL;
}
static inline void *
queue_dequeue (struct queue *q)
{
struct item *r = q->head;
if (r == NULL)
return NULL;
/* Pop the first item off. */
if ((q->head = q->head->next) == NULL)
/* The queue is empty, fix tail pointer. */
q->tail = &q->head;
r->next = NULL;
return r;
}
static inline bool
queue_empty (struct queue *q)
{
return q->head == NULL;
}
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