queue.c

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/* -*- C -*- */
/*
 * Copyright (c) 2011-2020 Seagate Technology LLC and/or its Affiliates
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * For any questions about this software or licensing,
 * please email opensource@seagate.com or cortx-questions@seagate.com.
 *
 */


#include "lib/queue.h"
#include "lib/assert.h"
#include "lib/misc.h"    /* NULL */

#define EOQ ((struct m0_queue_link *)8)

const struct m0_queue M0_QUEUE_INIT = {
        .q_head = EOQ,
        .q_tail = EOQ
};

M0_INTERNAL void m0_queue_init(struct m0_queue *q)
{
        q->q_head = q->q_tail = EOQ;
        M0_ASSERT(m0_queue_invariant(q));
}

M0_INTERNAL void m0_queue_fini(struct m0_queue *q)
{
        M0_ASSERT(m0_queue_invariant(q));
        M0_ASSERT(m0_queue_is_empty(q));
}

M0_INTERNAL bool m0_queue_is_empty(const struct m0_queue *q)
{
        M0_ASSERT_EX(m0_queue_invariant(q));
        return q->q_head == EOQ;
}

M0_INTERNAL void m0_queue_link_init(struct m0_queue_link *ql)
{
        ql->ql_next = NULL;
}

M0_INTERNAL void m0_queue_link_fini(struct m0_queue_link *ql)
{
        M0_ASSERT(!m0_queue_link_is_in(ql));
}

M0_INTERNAL bool m0_queue_link_is_in(const struct m0_queue_link *ql)
{
        return ql->ql_next != NULL;
}

M0_INTERNAL bool m0_queue_contains(const struct m0_queue *q,
                                   const struct m0_queue_link *ql)
{
        struct m0_queue_link *scan;

        M0_ASSERT(m0_queue_invariant(q));
        for (scan = q->q_head; scan != EOQ; scan = scan->ql_next) {
                M0_ASSERT(scan != NULL);
                if (scan == ql)
                        return true;
        }
        return false;
}

M0_INTERNAL size_t m0_queue_length(const struct m0_queue *q)
{
        size_t length;
        struct m0_queue_link *scan;

        M0_ASSERT_EX(m0_queue_invariant(q));

        for (length = 0, scan = q->q_head; scan != EOQ; scan = scan->ql_next)
                ++length;
        return length;
}

M0_INTERNAL struct m0_queue_link *m0_queue_get(struct m0_queue *q)
{
        struct m0_queue_link *head;

        /* invariant is checked on entry to m0_queue_is_empty() */
        if (m0_queue_is_empty(q))
                head = NULL;
        else {
                head = q->q_head;
                q->q_head = head->ql_next;
                if (q->q_head == EOQ)
                        q->q_tail = EOQ;
                head->ql_next = NULL;
        }
        M0_ASSERT_EX(m0_queue_invariant(q));
        return head;

}

M0_INTERNAL void m0_queue_put(struct m0_queue *q, struct m0_queue_link *ql)
{
        /* invariant is checked on entry to m0_queue_is_empty() */
        if (m0_queue_is_empty(q))
                q->q_head = ql;
        else
                q->q_tail->ql_next = ql;
        q->q_tail = ql;
        ql->ql_next = EOQ;
        M0_ASSERT_EX(m0_queue_invariant(q));
}

M0_INTERNAL bool m0_queue_invariant(const struct m0_queue *q)
{
        struct m0_queue_link *scan;

        if ((q->q_head == EOQ) != (q->q_tail == EOQ))
                return false;
        if (q->q_head == NULL || q->q_tail == NULL)
                return false;

        for (scan = q->q_head; scan != EOQ; scan = scan->ql_next) {
                if (scan == NULL || scan == EOQ)
                        return false;
        }
        if (q->q_head != EOQ && q->q_tail->ql_next != EOQ)
                return false;
        return true;
}

/*
 *  Local variables:
 *  c-indentation-style: "K&R"
 *  c-basic-offset: 8
 *  tab-width: 8
 *  fill-column: 80
 *  scroll-step: 1
 *  End:
 */