Why is pthread_join not returning? - c

Question

I think pthread_join should always return a value and then allow the main thread to process code after that. In my past experience, this will work. But now I am stuck with it. Somehow it just doesn't return and block the main thread. Or may it is the main thread that executes the task. I don't know why. In the code below, I cannot reach "Thread created2" until I terminate the client. Any idea?
int main(int argc, char *argv[]) {
int sockfd, port; /* listen on sock_fd, new connection on new_fd */
struct sockaddr_in my_addr; /* my address information */
struct sockaddr_in their_addr; /* connector's address information */
socklen_t sin_size;
if(signal(SIGINT, sigintEvent) == SIG_ERR)
printf("can't catch SIGINT!");
/* generate the socket */
if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
perror("socket");
exit(1);
}
if (argc > 1) {
port = atoi(argv[1]);
} else {
port = MYPORT;
}
/* generate the end point */
my_addr.sin_family = AF_INET; /* host byte order */
my_addr.sin_port = htons(port); /* short, network byte order */
my_addr.sin_addr.s_addr = INADDR_ANY; /* auto-fill with my IP */
/* bzero(&(my_addr.sin_zero), 8); ZJL*/ /* zero the rest of the struct */
/* bind the socket to the end point */
if (bind(sockfd, (struct sockaddr *)&my_addr, sizeof(struct sockaddr)) \
== -1) {
perror("bind");
exit(1);
}
/* start listnening */
if (listen(sockfd, MAXCONNECTIONS) == -1) {
perror("listen");
exit(1);
}
createPool(MAXCONNECTIONS);
/* create a node pointer as head of the list */
head = (node*)malloc(sizeof(node));
openFile();
printf("server starts listnening ...\n");
int new_fd;
sin_size = sizeof(struct sockaddr_in);
while((new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size))) {
printf("Accepted!\n");
printf("server: got connection!\n");
//tNode* tThread = (tNode*)threadDequeue();
pthread_t pt;
printf("Got tThread.\n");
if((pthread_create(&pt, NULL, runService,(void*)&new_fd)) != 0) {
printf("error creating thread.");
abort();
}
printf("Thread created.\n");
if( pthread_join(pt, NULL) != 0 ) {
printf("error joining thread");
abort();
}
printf("Thread created2.\n");
}
exit(1);
}

Answer 1

From the documentation we can read the following information about pthread_join
The pthread_join() function waits for the thread specified by
thread
to terminate. If that thread has already terminated, then
pthread_join() returns immediately. The thread specified by thread
must be joinable.
This indicates that in your case parent thread is waiting for the completion of its child thread pt. The child thread pt which is executing the runService is still not returned/completed. Hence your parent thread would keep on waiting for completion( not returning from pthread_join method).
You should try to review the code of runService to understand this situation.