[英]How to properly terminate a pthread?
我有一個TCP回顯服務器,該服務器為連接到它的每個客戶端創建一個pthread。 對於每個連接,我都有一個遞增的變量nbOfClients
。 當客戶端關閉其連接時,我會檢測到該連接並減少客戶端數量。 但是,服務器一直認為客戶端還活着,並繼續嘗試從套接字讀取/寫入。 我猜想那是由於創建客戶端的線程pthread_cancel
,我試圖使用pthread_cancel
殺死該線程,但全部無效。 我想殺死與某個關閉其連接的客戶端關聯的pthread。 我該怎么辦?
這是我的代碼:
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);
}
}
}
}
謝謝。
您應該在為客戶端提供服務的線程中檢查read()
是否返回0
,因為如果對等方(此處的客戶端)關閉了連接,則read()
返回0
。
在這行之后
n = read((int)arg, buf, BUFSIZE);
加
if (0 == n)
{
fprintf(stderr, "The client closed the connection.\n");
break;
}
就在線程函數離開之前,您可以添加該語句以減少正在運行的線程數。
還應注意,所有“客戶端”線程以及主線程會同時訪問nbOfClients
,因此應保護其訪問,例如通過使用互斥鎖。
還有另一個問題,因為對讀取的緩沖區的strlen()
的調用期望緩沖區為0
終止,即使您發送了0
終止的“字符串”,也不一定需要這種情況。 read()
可能會返回客戶端發送的“字符串”,而不是一部分。 因此,循環遍歷read()
直到接收到0
終止符。
不要通過調用pthread_cancel()
使線程本身結束,而應使用pthread_exit()
。
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