2019独角兽企业重金招聘Python工程师标准>>>

struct sigevent

{

int sigev_notify; //notification type    SIGEV_{NONE, SIGNAL, THREAD}

int sigev_signo; //signal number if SIGEV_SIGNAL

union sigval   sigev_value; // passed to signal handler or thread

// following two is SIGEV_THREAD

void (*sigev_notify_function)(union sigval);

pthread_attr_t *sigev_notify_attributes;

}

union sigval

{

int sival_int; //integer value

void *sival_ptr; //pointer value

}

//mqnotifysig4.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <mqueue.h>
#include <signal.h>
#include <errno.h>int main(int argc, char **argv)
{int signo;mqd_t mqd;void *buff;ssize_t n;sigset_t newmask;struct mq_attr attr;struct sigevent sigev;if (argc != 2) {printf("usage: mqnotifysig3 <name>");exit(0);}mqd = mq_open(argv[1], O_RDONLY | O_NONBLOCK);mq_getattr(mqd, &attr);buff = malloc(attr.mq_msgsize);sigemptyset(&newmask);sigaddset(&newmask, SIGUSR1);sigprocmask(SIG_BLOCK, &newmask, NULL);sigev.sigev_notify = SIGEV_SIGNAL;sigev.sigev_signo = SIGUSR1;mq_notify(mqd, &sigev);for ( ; ; ) {sigwait(&newmask, &signo);if (signo == SIGUSR1) {mq_notify(mqd, &sigev);while ((n = mq_receive(mqd, buff, attr.mq_msgsize, NULL)) >= 0) {printf("reda %ld bytes\n",(long) n);}if (errno != EAGAIN) {printf("mq_receive error");exit(0);}}}exit(0);
}

消息队列描述符并不是普通的文件描述符，所以我们无法使用select机制来高效率的处理，但是我们可以模仿出来，通过在信号处理函数中，往一个管道写入一个字符，那么在主线程中select此管道描述就OK 了。

例子：

代码：

//mqnotifysig5.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <mqueue.h>
#include <signal.h>
#include <errno.h>int pipefd[2];
static void sig_usr1(int);int main(int argc, char **argv)
{int nfds;char c;fd_set rset;mqd_t mqd;ssize_t n;void *buff;struct mq_attr attr;struct sigevent sigev;if (argc != 2) {printf("usage: mq_notifysig5 <name>");exit(0);}mqd = mq_open(argv[1], O_RDONLY | O_NONBLOCK);mq_getattr(mqd, &attr);buff = malloc(attr.mq_msgsize);pipe(pipefd);signal(SIGUSR1, sig_usr1);sigev.sigev_notify = SIGEV_SIGNAL;sigev.sigev_signo = SIGUSR1;mq_notify(mqd, &sigev);FD_ZERO(&rset);for ( ; ; ) {FD_SET(pipefd[0], &rset);nfds = select(pipefd[0] + 1, &rset, NULL, NULL, NULL);if (FD_ISSET(pipefd[0], &rset)) {read(pipefd[0], &c, 1);mq_notify(mqd, &sigev);while ((n = mq_receive(mqd, buff, attr.mq_msgsize, NULL)) >= 0) {printf("read %ld bytes\n", (long) n);}if (errno != EAGAIN) {printf("mq_receive error");exit(0);}}}exit(0);
}static void sig_usr1(int signo)
{write(pipefd[1], "", 1);return;
}

异步事件通知的另一种方式是把sigev_notify设置成SIGEV_THREAD，这样当一消息放到一个空的队列上，会创建一个线程。

例子：

代码：

//mqnotifysigthread1.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <mqueue.h>
#include <signal.h>
#include <errno.h>
mqd_t mqd;
struct mq_attr attr;
struct sigevent sigev;static void notify_thread(union sigval);int main(int argc, char **argv)
{if (argc != 2) {printf("usage: mqnotifythread1 <name>");exit(0);}mqd = mq_open(argv[1], O_RDONLY | O_NONBLOCK);mq_getattr(mqd, &attr);sigev.sigev_notify = SIGEV_THREAD;sigev.sigev_value.sival_ptr = NULL;sigev.sigev_notify_function = notify_thread;sigev.sigev_notify_attributes = NULL;mq_notify(mqd, &sigev);for ( ; ; ) pause;exit(0);
}static void notify_thread(union sigval arg)
{ssize_t n;void *buff;printf("notify_thread started\n");buff = malloc(attr.mq_msgsize);mq_notify(mqd, &sigev);while ((n = mq_receive(mqd, buff, attr.mq_msgsize, NULL)) >= 0) {printf("read %ld bytes\n", (long) n);}if (errno != EAGAIN) {printf("mq_receive error\n");exit(0);}free(buff);pthread_exit(NULL);
}