qlock.h

#include <stdlib.h>

struct msg {
        struct msg *next;
};

struct queue {
        struct msg *head;
        struct msg *tail;
        int lock;
};

#define LOCK(q) while (__sync_lock_test_and_set(&(q)->lock,1)) {}
#define UNLOCK(q) __sync_lock_release(&(q)->lock);

static inline struct queue *
qinit(void)
{
        struct queue *q = calloc(1, sizeof(*q));
        return q;
}

static inline int
push(struct queue *q, struct msg *m)
{
        LOCK(q)
        if (q->tail) {
                q->tail->next = m;
                q->tail = m;
        } else {
                q->head = q->tail = m;
        }
        UNLOCK(q)

        return 0;
}

static inline struct msg *
pop(struct queue *q)
{
        struct msg *m;

        LOCK(q)
        m = q->head;
        if (m) {
                q->head = m->next;
                if (q->head == NULL) {
                        q->tail = NULL;
                }
                m->next = NULL;
        }
        UNLOCK(q)

        return m;
}