Add queue library

This commit adds a queue library as a wrapper around the list library

os/lib/queue.h

@@ -0,0 +1,143 @@
+/*
+ * Copyright (c) 2017, George Oikonomou - http://www.spd.gr
+ * Copyright (c) 2017, James Pope
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the copyright holder nor the names of its
+ *    contributors may be used to endorse or promote products derived
+ *    from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+/*---------------------------------------------------------------------------*/
+/**
+ * \addtogroup data
+ * @{
+ *
+ * \defgroup queue Queue library
+ *
+ * This library provides functions for the creation and manipulation of
+ * queues. The library is implemented as a wrapper around the list library.
+ *
+ * A queue is declared using the QUEUE macro. Queue elements must be
+ * allocated by the calling code and must be of a C struct datatype. In this
+ * struct, the first field must be a pointer called \e next. This field will
+ * be used by the library to maintain the queue. Application code must not
+ * modify this field directly.
+ * @{
+ */
+/*---------------------------------------------------------------------------*/
+#ifndef QUEUE_H_
+#define QUEUE_H_
+/*---------------------------------------------------------------------------*/
+#include "contiki.h"
+#include "lib/list.h"
+
+#include <stdbool.h>
+/*---------------------------------------------------------------------------*/
+/**
+ * \brief The queue data type
+ */
+typedef list_t queue_t;
+/*---------------------------------------------------------------------------*/
+/**
+ * \brief Define a queue.
+ *
+ * This macro defines a queue.
+ *
+ * The datatype for elements must be a C struct. The struct's first member must
+ * be a pointer called \e next. This is used internally by the library to
+ * maintain data structure integrity and must not be modified directly by
+ * application code.
+ *
+ * \param name The name of the queue.
+ */
+#define QUEUE(name) LIST(name)
+/*---------------------------------------------------------------------------*/
+struct queue {
+  struct queue *next;
+};
+/*---------------------------------------------------------------------------*/
+/**
+ * \brief Initialise a queue
+ * \param queue The queue
+ */
+static inline void
+queue_init(queue_t queue)
+{
+  list_init(queue);
+}
+/*---------------------------------------------------------------------------*/
+/**
+ * \brief Adds an element to the tail of the queue
+ * \param queue The queue
+ * \param element A pointer to the element to be added
+ */
+static inline void
+queue_enqueue(queue_t queue, void *element)
+{
+  list_add(queue, element);
+}
+/*---------------------------------------------------------------------------*/
+/**
+ * \brief Removes the element at the front of the queue
+ * \param queue The queue
+ * \return A pointer to the element removed
+ *
+ * If this function returns NULL if the queue was empty (queue underflow)
+ */
+static inline void *
+queue_dequeue(queue_t queue)
+{
+  return list_pop(queue);
+}
+/*---------------------------------------------------------------------------*/
+/**
+ * \brief Returns the front element of the queue, without removing it
+ * \param queue The queue
+ * \return A pointer to the element at the front of the queue
+ */
+static inline void *
+queue_peek(queue_t queue)
+{
+  return list_head(queue);
+}
+/*---------------------------------------------------------------------------*/
+/**
+ * \brief Check if a queue is empty
+ * \param queue The queue
+ * \retval true The queue is empty
+ * \retval false The queue has at least one element
+ */
+static inline bool
+queue_is_empty(queue_t queue)
+{
+  return *queue == NULL ? true : false;
+}
+/*---------------------------------------------------------------------------*/
+#endif /* QUEUE_H_ */
+/*---------------------------------------------------------------------------*/
+/**
+ * @}
+ * @}
+ */