与epoll一起使用时,非阻止插座RECV问题
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01-10-2019 - |
题
我有一个问题:有时(不是定期)recv返回 -1
和 errno == EAGAIN
使用时 epoll
在 edge-triggered
模式。代码:
server_sock = startup(&port);
if ( (epollfd = epoll_create(4096)) < 0) {
perror("epoll_create error");
exit(EXIT_FAILURE);
}
ev.events = EPOLLIN | EPOLLET;
ev.data.fd = server_sock;
if (epoll_ctl(epollfd, EPOLL_CTL_ADD, server_sock, &ev) == -1) {
perror("epoll_ctl: server_sock");
exit(EXIT_FAILURE);
}
while (1) {
int nfds = epoll_wait(epollfd, events, 4096, -1);
if (nfds == -1) {
perror("epoll_wait");
exit(EXIT_FAILURE);
}
for (int i = 0; i < nfds; i++) {
if (events[i].data.fd == server_sock) {
client_sock = accept(server_sock,
(struct sockaddr *)&client_name,
(socklen_t *)(&client_name_len));
if (client_sock == -1) //server overloaded
continue;
if (events[i].events & EPOLLIN) {
std::cout << "EPOLLIN on " << client_sock << std::endl;
}
Arch::set_nonblocking(client_sock);
ev.events = EPOLLIN | EPOLLRDHUP | EPOLLET; //input data and connection closing
ev.data.fd = client_sock;
if (epoll_ctl(epollfd, EPOLL_CTL_ADD, client_sock, &ev) == -1) {
perror("epoll_ctl: client_socket");
exit(EXIT_FAILURE);
}
accept_request(client_sock);
} else {
if (events[i].events & EPOLLRDHUP) {
epoll_ctl(epollfd, EPOLL_CTL_DEL, events[i].data.fd, &ev);
}
}
}
}
startup(&port)
创建非阻止插座,与端口绑定等。我的脚本发送以下数据:GET /connect?id=1&secret=1 HTTP/1.0\r\n\r\n
但有时候 recv
返回 -1
在此功能中(在内部呼叫 accept_request
) :
/**********************************************************************/
/* Get a line from a socket, whether the line ends in a newline,
* carriage return, or a CRLF combination. Terminates the string read
* with a null character. If no newline indicator is found before the
* end of the buffer, the string is terminated with a null. If any of
* the above three line terminators is read, the last character of the
* string will be a linefeed and the string will be terminated with a
* null character.
* Parameters: the socket descriptor
* the buffer to save the data in
* the size of the buffer
* Returns: the number of bytes stored (excluding null) */
/**********************************************************************/
int get_line(int sock, char *buf, int size) {
int i = 0;
char c = '\0';
int n;
while ((i < size - 1) && (c != '\n')) {
n = recv(sock, &c, 1, 0);
//debug
std::cout << "n = " << n << std::endl;
if (n > 0) {
if (c == '\r') {
n = recv(sock, &c, 1, MSG_PEEK);
if ((n > 0) && (c == '\n'))
recv(sock, &c, 1, 0);
else
c = '\n';
}
buf[i] = c;
i++;
} else {
//debug
if (errno == EWOULDBLOCK)
std::cout << "EWOULDBLOCK" << std::endl;
c = '\n';
}
}
buf[i] = '\0';
return(i);
}
正如Epoll Man Page写的那样,我必须阅读/写作,直到我得到 EAGAIN
, ,但是我已经知道了!而且我确定缓冲区不会空。我做错了什么?
UPD: 我发现了一个有趣的事情:当发生这种情况时,我在代码中使用 sleep(1)
和 recc(...)
再次,我得到了我期望的数据!这是一个肮脏的把戏。还有其他优雅的方法可以解决这个问题吗?
解决方案
第一个完全正常 recv()
在这种情况下要返回 EAGAIN
. epoll()
从来没有告诉过您是否可以阅读。
每一个 recv()
应该准备好处理 EAGAIN
如果您使用的是非阻滞插座。出现虚假的唤醒是可能的,因此每当API喜欢 select()
, poll()
或者 epoll()
告诉您插座是可以读取的,只是说“它 可能 可读 - 尝试一下。
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