epoll_wait阻塞信號插座

Question

打擾我的長篇文章。我會發布代碼，以便更容易理解我面臨的問題。看起來如果一個有信號的套接字被添加到epoll實例中，那麼epoll實例上的epoll_wait將不會被阻塞。下面的例子已經讓我相信這一點：

#include <sys/socket.h> 
#include <netinet/in.h> 
#include <arpa/inet.h> 
#include <stdio.h> 
#include <stdlib.h> 
#include <unistd.h> 
#include <errno.h> 
#include <string.h> 
#include <sys/types.h> 
#include <time.h> 
#include <sys/epoll.h> 

int MAX_EVENT_COUNT = 10; 

int main(int argc, char *argv[]) 
{ 

int epollfd = epoll_create(MAX_EVENT_COUNT); 
if (epollfd == -1) 
{ 
printf("\n Error : epoll_create \n"); 
return 1; 
} 

epoll_event ev; 
memset(&ev,0,sizeof(ev)); 
ev.events = EPOLLIN | EPOLLET; 

int pipefd[2]; 
if (pipe(pipefd) == -1) 
{ 
perror("pipe"); 
exit(EXIT_FAILURE); 
} 

char ch = 'a'; 
write(pipefd[1], &ch, 1); 

if (epoll_ctl(epollfd , EPOLL_CTL_ADD, pipefd[0], &ev) == -1) 
{ 
printf("\n Error : epoll add result \n"); 
return 1; 
} 

epoll_event rawResult [MAX_EVENT_COUNT]; 
int32_t res = epoll_wait(epollfd, rawResult, MAX_EVENT_COUNT, -1); 

if(res!=1) 
{ 
printf("\n Epoll problem \n"); 
} 
else 
{ 
printf("\n OK \n"); 
} 

} 

但是下面的例子是幾乎相同的，但這次我一個信號插座添加到epoll的，此時epoll_wait調用塊

#include <sys/socket.h> 
#include <netinet/in.h> 
#include <arpa/inet.h> 
#include <stdio.h> 
#include <stdlib.h> 
#include <unistd.h> 
#include <errno.h> 
#include <string.h> 
#include <sys/types.h> 
#include <time.h> 
#include <sys/epoll.h> 

int MAX_EVENT_COUNT = 10; 

int main(int argc, char *argv[]) 
{ 
int listenfd = 0; 
{ 
struct sockaddr_in serv_addr; 

char sendBuff[1025]; 

listenfd = socket(AF_INET, SOCK_STREAM, 0); 
memset(&serv_addr, '0', sizeof(serv_addr)); 
memset(sendBuff, '0', sizeof(sendBuff)); 

serv_addr.sin_family = AF_INET; 
serv_addr.sin_addr.s_addr = htonl(INADDR_ANY); 
serv_addr.sin_port = htons(5000); 

bind(listenfd, (struct sockaddr*)&serv_addr, sizeof(serv_addr)); 

listen(listenfd, 10); 
} 


int sockfd = 0, n = 0; 
char recvBuff[1024]; 
struct sockaddr_in serv_addr; 

memset(recvBuff, '0',sizeof(recvBuff)); 
if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) 
{ 
printf("\n Error : Could not create socket \n"); 
return 1; 
} 

memset(&serv_addr, '0', sizeof(serv_addr)); 

serv_addr.sin_family = AF_INET; 
serv_addr.sin_port = htons(5000); 

if(inet_pton(AF_INET, "127.0.0.1", &serv_addr.sin_addr)<=0) 
{ 
printf("\n inet_pton error occured\n"); 
return 1; 
    } 

if(connect(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) 
{ 
printf("\n Error : Connect Failed \n"); 
return 1; 
} 

int connfd = accept(listenfd, (struct sockaddr*)NULL, NULL); 
int epollfd = epoll_create(MAX_EVENT_COUNT); 
if (epollfd == -1) 
{ 
printf("\n Error : epoll_create \n"); 
return 1; 
} 

epoll_event ev; 
memset(&ev,0,sizeof(ev)); 
ev.events = EPOLLIN | EPOLLET; 

if (epoll_ctl(epollfd , EPOLL_CTL_ADD, sockfd, &ev) == -1) 
{ 
printf("\n Error : epoll add result \n"); 
return 1; 
} 

epoll_event rawResult [MAX_EVENT_COUNT]; 
int32_t res = epoll_wait(epollfd, rawResult, MAX_EVENT_COUNT, -1); 

} 

Answer 1

如果它正在等待的文件描述符沒有事件供其報告，epoll_wait()將會阻塞。就你而言，我不相信你已經達到了epoll_wait()。假設你的程序已經通過了connect()和accept()，那麼你沒有在連接上寫任何數據（在sockfd上），所以epoll_wait()將不會檢測到connfd上的任何事件。

這與您的第一個程序有所不同，在pipefd[1]上寫入一個字節的數據之前，請致電pipefd[0]上的epoll_wait()。