linux epoll系列5 解除epoll_wait状态
有时候会有解除epoll_wait状态的需求。
实现方法：
1，给执行epoll_wait的程序发signal。
2，使用sockpair。
1，给执行epoll_wait的程序发signal。
#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <errno.h>
#include <sys/epoll.h>
void sigusr1_handler(int sig){
write(fileno(stdout), "signal called\n", 14);
}
int main(){
int nfds;
int epfd;
signal(SIGUSR1, sigusr1_handler);
epfd = epoll_create(1);
if(epfd < 0){
perror("epoll_crreate");
return 1;
}
printf("before epoll_wait\n");
//一直等下去
nfds = epoll_wait(epfd, NULL, 1, -1);
printf("after epoll_wait:%d\n", nfds);
printf("%d\n", errno);
perror("perror after epoll_wait");
return 0;
}
执行方法：
1，执行程序
2，先用下面的命令找到当前执行程序的PID
ps -e | grep a.out
结果：
ys@ys-VirtualBox:~/cpp/network$ ps -e | grep a.out
2882 pts/0 00:00:00 a.out
3，给个执行中的程序发signal
kill -s SIGUSR1 2882
结果：
before epoll_wait
signal called
after epoll_wait:-1
4
perror after epoll_wait: Interrupted system call
2，使用sockpair。
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/epoll.h>
#define EVENTS 8
int soc[2];
void processA(){
sleep(3);
printf("processA: send message\n");
write(soc[0], "HELLO\n", 6);
return;
}
void processB(){
int epfd;
epoll_event ev, ev_ret[EVENTS];
int nfds;
int i;
char buf[128];
epfd = epoll_create(1);
if(epfd < 0){
perror("epoll_create");
return ;
}
memset(&ev, 0, sizeof(ev));
ev.events = EPOLLIN;
ev.data.fd = soc[1];
if(epoll_ctl(epfd, EPOLL_CTL_ADD, soc[1], &ev) != 0){
perror("epoll_clt");
return ;
}
memset(&ev, 0, sizeof(ev));
ev.events = EPOLLIN;
ev.data.fd = fileno(stdin);
if(epoll_ctl(epfd, EPOLL_CTL_ADD, fileno(stdin), &ev) != 0){
perror("epoll_clt1");
return ;
}
while(1){
printf("before epoll_wait\n");
nfds = epoll_wait(epfd, ev_ret, EVENTS , -1);
if(nfds < 0){
perror("epoll_wait");
return;
}
printf("after epoll_wait\n");
for(i = 0; i < nfds; ++i){
if(ev_ret[i].data.fd == soc[1]){
printf("processB:break message from socketpair\n");
goto outofloop;
}
else if(ev_ret[i].data.fd == fileno(stdin)){
read(fileno(stdin), buf, sizeof(buf));
printf("processB:input from stdin\n");
}
}
}
outofloop:
printf("process B:outside of loop\n");
return ;
}
int main(){
int ret;
ret = socketpair(AF_UNIX, SOCK_STREAM, 0, soc);
if(ret != 0){
perror("socketpair");
return 1;
}
if(fork() == 0){
processA();
}
else{
processB();
}
return 0;
}