UNPv2第五章：Posix消息队列

#include<mqueue.h>
mqd_t mq_open(const cahr *name, int flag, …)
    //返回：成功时为消息队列描述字，出错时为-1

#include<mqueue.h>
Int mq_close(mqd_t mqdes);
    //返回：成功时为0，出错时为-1

#include<mqueue.h>
Int mq_unlink(const char *name);
    //返回：成功时为0，出错时为-1

#include<mqueue.h>
int mq_getattr(mqd_t mqdes, struct mq_attr *attr);
int mq_setattr(mqd_t mqdes, const struct mq_attr *attr, struct mq_attr *oattr);
    //返回：成功返回0，失败返回－1。

struct mq_attr{
    long mq_flags;    /* Message queue flags：0，O_NONBLOCK */
    long mq_maxmsg;   /* Maximum number of messages.  */
    long mq_msgsize;  /* Maximum message size.  */
    long mq_curmsgs;  /* Number of messages currently queued.  */
};

#include<mqueue.h>
int mq_send(mqd_t mqdes, const char *ptr, size_t len, unsigned int prio);
    //返回：成功时返回0，出错返回-1
ssize_t mq_receive(mqd_t mqdes, char *ptr, size_t len, unsigned int *proip);
    //返回：成功为消息中的字节数，出错为-1

#include<mqueue.h>
int mq_notify(mqd_t mqdes, const struct sigevent *notification);
    返回：成功时为0，出错时为-1

union sigval {
        int sival_int;
        void    *sival_ptr;
} 
struct sigevent {
        union sigval    sigev_value;
        int         sigev_signo;
        int         sigev_notify;
        void        (*sigev_notify_function)(union sigval);
        pthread_attr_t  *sigev_notify_attributes;
}