我创建了一个TCP服务器套接字,它监听connect()请求并接受它们。在接受客户机套接字之后,它接收来自它的数据。我希望recv()函数在超时的情况下阻塞,但它似乎是非阻塞的。
我已经实现了客户机在接收服务器响应时处于阻塞模式,但它在服务器端的工作方式似乎不同。
在下面,复制粘贴要在阻止模式下接收数据的服务器端:
int clientSocket = accept(_serverSocket, (struct sockaddr *)NULL, NULL);
if (clientSocket < 0)
return -1;
// set TIMEOUT option to server socket
struct timeval tv;
tv.tv_sec = 0;
tv.tv_usec = 500 * 1000;
int sockOptRet = setsockopt(clientSocket, SOL_SOCKET, SO_RCVTIMEO, (const char*)&tv, sizeof tv);
struct linger sl;
sl.l_onoff = 1; /* non-zero value enables linger option in kernel */
sl.l_linger = 0; /* timeout interval in seconds */
setsockopt(clientSocket, SOL_SOCKET, SO_LINGER, &sl, sizeof(sl));
char _rcvBuffer[sizeof(can_frame)];
int numBytesRcv = recv(clientSocket, _rcvBuffer, sizeof(can_frame), 0);
我也尝试过用MSG_WAITALL flag,但它没有改变任何东西。。。
最佳答案
你的代码应该被明显屏蔽,但是你0.5秒的超时并不能证明它是正确的。
如果将超时时间增加到更明显的值,例如2s,并将代码移植到beej's tpc server template,则会得到如下结果:
/*
** server.c -- a stream socket server demo
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <sys/wait.h>
#include <signal.h>
#define PORT "3490" // the port users will be connecting to
#define BACKLOG 10 // how many pending connections queue will hold
void sigchld_handler(int s)
{
// waitpid() might overwrite errno, so we save and restore it:
int saved_errno = errno;
while(waitpid(-1, NULL, WNOHANG) > 0);
errno = saved_errno;
}
// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa)
{
if (sa->sa_family == AF_INET) {
return &(((struct sockaddr_in*)sa)->sin_addr);
}
return &(((struct sockaddr_in6*)sa)->sin6_addr);
}
int main(void)
{
int sockfd, new_fd; // listen on sock_fd, new connection on new_fd
struct addrinfo hints, *servinfo, *p;
struct sockaddr_storage their_addr; // connector's address information
socklen_t sin_size;
struct sigaction sa;
int yes=1;
char s[INET6_ADDRSTRLEN];
int rv;
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = AI_PASSIVE; // use my IP
if ((rv = getaddrinfo(NULL, PORT, &hints, &servinfo)) != 0) {
fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
return 1;
}
// loop through all the results and bind to the first we can
for(p = servinfo; p != NULL; p = p->ai_next) {
if ((sockfd = socket(p->ai_family, p->ai_socktype,
p->ai_protocol)) == -1) {
perror("server: socket");
continue;
}
if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &yes,
sizeof(int)) == -1) {
perror("setsockopt");
exit(1);
}
if (bind(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
close(sockfd);
perror("server: bind");
continue;
}
break;
}
freeaddrinfo(servinfo); // all done with this structure
if (p == NULL) {
fprintf(stderr, "server: failed to bind\n");
exit(1);
}
if (listen(sockfd, BACKLOG) == -1) {
perror("listen");
exit(1);
}
sa.sa_handler = sigchld_handler; // reap all dead processes
sigemptyset(&sa.sa_mask);
sa.sa_flags = SA_RESTART;
if (sigaction(SIGCHLD, &sa, NULL) == -1) {
perror("sigaction");
exit(1);
}
printf("server: waiting for connections...\n");
while(1) { // main accept() loop
sin_size = sizeof their_addr;
new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size);
if (new_fd == -1) {
perror("accept");
continue;
}
inet_ntop(their_addr.ss_family,
get_in_addr((struct sockaddr *)&their_addr),
s, sizeof s);
printf("server: got connection from %s\n", s);
if (!fork()) { // this is the child process
close(sockfd); // child doesn't need the listener
// set TIMEOUT option to server socket
struct timeval tv;
tv.tv_sec = 2;
tv.tv_usec = 0 * 500 * 1000;
int sockOptRet = setsockopt(new_fd, SOL_SOCKET, SO_RCVTIMEO, (const char*)&tv, sizeof tv);
struct linger sl;
sl.l_onoff = 1; /* non-zero value enables linger option in kernel */
sl.l_linger = 0; /* timeout interval in seconds */
setsockopt(new_fd, SOL_SOCKET, SO_LINGER, &sl, sizeof(sl));
char can_frame[1024];
char _rcvBuffer[sizeof(can_frame)];
int numBytesRcv = recv(new_fd, _rcvBuffer, sizeof(can_frame), 0);
if (send(new_fd, "Hello, world!", 13, 0) == -1)
perror("send");
close(new_fd);
exit(0);
}
close(new_fd); // parent doesn't need this
}
return 0;
}
现在,如果您运行此命令,然后执行以下操作:
nc localhost 3490
在不键入要发送的行的情况下,应该有明显的2秒等待
在服务器放弃之前,表明
recv
确实被阻塞了。关于linux - 为什么来自套接字的recv()不会阻塞,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/50647432/