我有一个 tcp echo 服务器,它为连接到它的每个客户端创建一个 pthread。对于每个连接,我都有一个递增的变量nbOfClients
。
当客户端关闭其连接时,我会检测到它并减少客户端数量。然而,服务器一直认为客户端还活着,并继续尝试从套接字读取/写入。我猜想这是因为创建了客户端的线程导致的,我尝试使用 pthread_cancel 来终止该线程,但没有成功。
我想终止与关闭其连接的某个客户端关联的 pthread。
我该怎么办?
这是我的代码:
static int nbOfClients = 0;
static pthread_t tid;
int main (int argc, char *argv[]) {
int bytes_to_read, arg, listen_sd, new_conn, sockfd, client_len, port;
struct sockaddr_in server, client_addr;
char *bp, buf[BUFLEN];
ssize_t n;
sockfd = 0;
switch(argc) {
case 1:
port = SERVER_TCP_PORT; // Use the default port
break;
case 2:
port = atoi(argv[1]); // Get user specified port
break;
default:
fprintf(stderr, "Usage: %s [port]\n", argv[0]);
exit(1);
}
// Create a stream socket
if ((listen_sd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
error("Cannot Create Socket!");
// set SO_REUSEADDR so port can be resused imemediately after exit, i.e., after CTRL-c
arg = 1;
if (setsockopt (listen_sd, SOL_SOCKET, SO_REUSEADDR, &arg, sizeof(arg)) == -1)
error("setsockopt");
// Bind an address to the socket
bzero((char *)&server, sizeof(server));
server.sin_family = AF_INET;
server.sin_port = htons(port);
server.sin_addr.s_addr = htonl(INADDR_ANY); // Accept connections from any client
if (bind(listen_sd, (struct sockaddr *)&server, sizeof(server)) == -1)
error("bind error");
listen(listen_sd, MAX_CONNECTIONS); ///put a define constant indicating the maximum number of clients #define NB_CLIENTS 3
while (TRUE) {
client_len = sizeof(client_addr);
if ((new_conn = accept(listen_sd, (struct sockaddr *) &client_addr, (socklen_t *)&client_len)) == -1)
error("accept error");
if(new_conn > 0) {
if(nbOfClients < MAX_CONNECTIONS) {
printf("just here\n");
printf(">> Initializing remote address: %s\n", inet_ntoa(client_addr.sin_addr));
nbOfClients++;
fclose(fp);
printf("Connections to date: %u \n",nbOfClients);
printf("make thread\n");
pthread_create(&tid,NULL,&echo, (void *)new_conn);
printf("had thread\n");
}
else {
printf("connection limit reached\n");
if(send(new_conn, "Server full!\n", 13, 0) == -1)
perror("send");
close(new_conn);
}
}
}
return(0);
}
void * echo(void *arg) {
char buf[BUFSIZE]; /* message buffer */
int n, i = 0;
bzero(buf, BUFSIZE);
if(send((int)arg, "Welcome!!\n", 20, 0) == -1)
perror("send");
detect_closed_connection(arg);
while(TRUE) {
n = read((int)arg, buf, BUFSIZE);
/**read: read input string from the client*/
if(n < 0) {
perror("error reading from socket");
}
printf("Server received from client, %d bytes: %s\n", n, buf);
/**write: echo the input string in UPPERCASE back to the client*/
int len = strlen(buf);
for(i = 0; buf[i]; i++)
buf[i] = toupper(buf[i]);
n = write((int)arg, buf, len);
if(n < 0) {
error("ERROR writing to socket");
}
}
}
void detect_closed_connection(void * listenSocket) {
struct pollfd pfd;
pfd.fd = (int)listenSocket;
pfd.events = POLLIN | POLLHUP | POLLRDNORM;
pfd.revents = 0;
while(pfd.revents == 0) {
if(poll(&pfd, 1, 100) > 0) {
// if result > 0, this means that there is either data available on the
// socket, or the socket has been closed
char buffer[32];
if (recv((int)listenSocket, buffer, sizeof(buffer), MSG_PEEK | MSG_DONTWAIT) == 0) {
// if recv returns zero, that means the connection has been closed:
nbOfClients--;
pthread_cancel(tid);
}
}
}
}
谢谢。
最佳答案
您应该检查 read()
在为客户端提供服务的线程中是否返回 0
,因为 read()
返回 0
以防对等方(此处为客户端)关闭连接。
此行之后
n = read((int)arg, buf, BUFSIZE);
添加
if (0 == n)
{
fprintf(stderr, "The client closed the connection.\n");
break;
}
就在线程函数离开之前,您可以添加语句来减少正在运行的线程数。
<小时/>另外请注意,nbOfClients
由所有“客户端”线程以及主线程同时访问,因此访问它应受到保护,例如通过使用互斥体。
还有另一个问题,因为在读取缓冲区时对 strlen()
的调用期望缓冲区以 0
终止,这不一定需要是情况下,即使您发送了以 0
结尾的“字符串”。 read()
很可能会返回客户端以多个部分发送的“字符串”。因此,循环 read()
直到收到 0
终止符。
不要通过调用pthread_cancel()
使线程自行结束,而是使用pthread_exit()
。
关于c - 如何正确终止 pthread?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/20303812/