针对epoll api的两种触发模式，lt和et，仿照一些例子写了代码进行实验。

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                  #define MAX_EVENT_NUMBER 1024#define BUFFER_SIZE 10int setnonblocking(int fd) { int old_option = fcntl(fd, F_GETFL); int new_option = old_option | O_NONBLOCK; fcntl(fd, F_SETFL, new_option); return old_option;}void addfd(int epollfd, int fd, bool enable_et) { epoll_event event; event.data.fd = fd; event.events = EPOLLIN; if (enable_et) { event.events |= EPOLLET; } epoll_ctl(epollfd, EPOLL_CTL_ADD, fd, &event); setnonblocking(fd);}void lt(epoll_event *events, int number, int epollfd, int listenfd) { char buf[BUFFER_SIZE]; for (int i=0; i
                  
                   = 3) { const char *ip =argv[2]; inet_pton(AF_INET, ip, &address.sin_addr); } else { address.sin_addr.s_addr = INADDR_ANY; } address.sin_port = htons(port); int listenfd = socket(PF_INET, SOCK_STREAM, 0); assert(listenfd >= 0); ret = bind(listenfd, (sockaddr*)&address, sizeof(address)); assert(ret != - 1); ret = listen(listenfd, 5); assert(ret != -1); epoll_event events[MAX_EVENT_NUMBER]; int epollfd = epoll_create(5); assert(epollfd != -1); addfd(epollfd, listenfd, true); while(true) { ret = epoll_wait(epollfd, events, MAX_EVENT_NUMBER, -1); if (ret < 0) { printf("epoll failure\n"); break; } lt(events, ret, epollfd, listenfd); // lt //et(events, ret, epollfd, listenfd); // et } close(listenfd); return 0;}
                  
                 
                
               
              
             
            
           
          
         
        
       
      
     

 

Makefile文件：

epoll_test : epoll_test.cpp        g++ -o epoll_test epoll_test.cpp -lpthread

 

以上程序有个问题，就是在端口被占用时候，因为bind失败，会assert失败然后core dump. 在重复测试时候，可以换个端口。

 

首先，注释掉et，使用lt:

lt(events, ret, epollfd, listenfd); // lt                //et(events, ret, epollfd, listenfd); // et

运行 ./epoll_test 12888 并在另一个窗口用telnet输入超过10个（BUFFERSIZE）字符：

$telnet 127.0.0.1 12888Trying 127.0.0.1...Connected to 127.0.0.1.Escape character is '^]'.12345678901234567890123456 1234567890123456789012345678

在服务器端得到：

$./epoll_test 12888lt event trigger onceget 9 bytes of content: 123456789lt event trigger onceget 9 bytes of content: 012345678lt event trigger onceget 9 bytes of content: 90123456lt event trigger onceget 1 bytes of content: lt event trigger onceget 9 bytes of content: 123456789lt event trigger onceget 9 bytes of content: 012345678lt event trigger onceget 9 bytes of content: 901234567lt event trigger onceget 3 bytes of content: 8

可以看出因为buffersize的限制，服务器端进行了多次读取，event也触发了多次。

 

换成et模式：

//lt(events, ret, epollfd, listenfd); // lt                et(events, ret, epollfd, listenfd); // et

运行服务器后，telnet客户端输入：

$telnet 127.0.0.1 12889Trying 127.0.0.1...Connected to 127.0.0.1.Escape character is '^]'.123456789012345678901234561234567890123456789012345678

服务器显示：

$./epoll_test 12889et event trigger onceget 9 bytes of content: 123456789get 9 bytes of content: 012345678get 9 bytes of content: 90123456get 1 bytes of content: read lateret event trigger onceget 9 bytes of content: 123456789get 9 bytes of content: 012345678get 9 bytes of content: 901234567get 3 bytes of content: 8read later

可以看出，每次客户端的字符串，只触发了一次。

 

其实，上面的例子还不够严谨，因为服务器一次已经把字符都读完了。那么如果没读完，会继续出发吗。

如下修改服务器代码：

//修改                        //while (true) {
                            if (true) {                                memset(buf, '\0', BUFFER_SIZE);                                int ret = recv(sockfd, buf, BUFFER_SIZE-1, 0);                                if (ret < 0) {                                        // Below shows complete                                        if ((errno == EAGAIN) || (errno == EWOULDBLOCK)) {                                                printf("read later\n");                                                break;                                        }                                        printf("some error happens\n");                                        close(sockfd);                                        //修改                                        //break;                                }                                else if (ret == 0) {                                        close(sockfd);                                        //修改                                        //break;                                }                                else {                                        printf("get %d bytes of content: %s\n", ret, buf);                                }                        }

运行服务器之后，telnet输入长字符串：

$telnet 127.0.0.1 12888Trying 127.0.0.1...Connected to 127.0.0.1.Escape character is '^]'.12345678901234567890123456

服务器端只显示了BUFFERSIZE长度的一行，没有读入的数据也没有进行event触发：

$./epoll_test 12888et event trigger onceget 9 bytes of content: 123456789

如果客户端，再输入一行：

$telnet 127.0.0.1 12888Trying 127.0.0.1...Connected to 127.0.0.1.Escape character is '^]'.123456789012345678901234561234567890123456789012345678

服务器端也仅仅把之前没读入的上一次客户端发来的数据中，再读入BUFFERSIZE长度：

$./epoll_test 12888et event trigger onceget 9 bytes of content: 123456789et event trigger onceget 9 bytes of content: 012345678

 

另外，对上面的服务器端程序，增加了et模式下对recv函数的返回ret=0的打印：

else if (ret == 0) {                                        printf("get 0 data\n");                                        close(sockfd);                                        break;                                }

发现在et模式下，没有走到ret==0的分支：

$telnet 127.0.0.1 12889Trying 127.0.0.1...Connected to 127.0.0.1.Escape character is '^]'.12345678901234567890123456

服务器端：

$./epoll_test 12889et event trigger onceget 9 bytes of content: 123456789get 9 bytes of content: 012345678get 9 bytes of content: 90123456get 1 bytes of content: read later

走的是如下的判断结束的分支：

if ((errno == EAGAIN) || (errno == EWOULDBLOCK)) {                                                printf("read later\n");                                                break;                                        }

以上。:)