Terminating secondary thread from another thread

[wssoh85]

Hi everyone, I'm new to this forum. If my qurestion is in wrong place please correct me.
I'm currently learning about the multithread, and TCP socket. But I was wondering why my code have problem. I search over google still cant fix my problem. Hope anyone can direct me into the right. Thanks

Basically, this is a TCP client program which do simple msg tranfsfer. When the connection establish, the thread "new_thr" will create another 2 thread which are "send_thr" and "recv_thr". One is to send message to server and another one is to receive message from server. At final, what I want is when either receive or user input an "Q" or "q", the whole process will terminated. So currently I m trying to use thread_cancel to terminate another thread.
Here is my code

[CODE]/* threadclient.c */
#include <pthread.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>

void *cthr_do();
void *cthr_send();
void *cthr_recv();


int main()
{    
    int k;
    pthread_t new_thr;
    int check = pthread_create(&new_thr, NULL, cthr_do, NULL );
    
    
    if(check!=0)
    printf("The thread cannot be created!");
    
    pthread_join (new_thr, NULL);
    
    printf("The whole process terminated\n");
    return 0;
}

void *cthr_do()
{    
    printf("thread run sucessful\n");

        int sock, bytes_received, connected, s, r;  
        char send_data[1024],recv_data[1024];
        struct hostent *host;
        struct sockaddr_in6 server_addr;  

        host = gethostbyname("::1");

        if ((sock = socket(AF_INET6, SOCK_STREAM, 0)) == -1) {
            perror("Socket");
            exit(1);
        }

        server_addr.sin6_family = AF_INET6;     
        server_addr.sin6_port = htons(5000);   
        server_addr.sin6_addr= in6addr_any/*((struct in_addr *)host->h_addr)*/;
        /*bzero(&(server_addr.sin_zero),8);*/
    /*memset(&(server_addr.sin_zero),0,8);*/
        
        connected = connect(sock, (struct sockaddr *)&server_addr, sizeof(server_addr));
         
    if (connected== -1) 
        {
            perror("Connect");
            exit(1);
        }

    printf("The connection is established.\n");    
    
    pthread_t send_thr, recv_thr;
              
              int chk_send = pthread_create(&send_thr, NULL, cthr_send, (void *)sock);
              if(chk_send!=0)
              printf("The send message thread cannot be created!");
              
              int chk_recv = pthread_create(&recv_thr, NULL, cthr_recv, (void *)sock);              
              if(chk_recv!=0)
              printf("The receive message thread cannot be created!");
              
              while (1)
              {
              s = pthread_join (send_thr, NULL);
              r = pthread_join (recv_thr, NULL);
              
              if (s && r)
              break;
              }
              
    close(sock);
    printf("closed socket\n");              
}


void *cthr_send(void *arg)
{          
          pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);
          pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, NULL);
          

          char send_data [1024], recv_data[1024]; 
          while (1)
          {
              printf("\n SEND (q or Q to quit) : ");
              gets(send_data)/*,1024,stdin)*/;
              
              if (strcmp(send_data , "q") == 0 || strcmp(send_data , "Q") == 0)
              {
                send((int) arg, send_data,strlen(send_data), 0);
                /*close ((int) arg);*/
                break;            
              }
               
              else
                 send((int) arg, send_data,strlen(send_data), 0);
              }  
              
              if ( pthread_cancel(recv_thr) == -1 ) 
              {
              perror("pthread_cancel failed");
              exit(3);
              }  
//              if (pthread_cancel(recv_thr)!= 0)
//              perror ("Thread cancelation ");              ;              
}

void *cthr_recv(void *arg)
{
         
              pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);
              pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, NULL);
              
              char send_data [1024] , recv_data[1024]; 
              int bytes_received;
              
              
              while (1)
              {
              bytes_received = recvfrom((int) arg, recv_data, 1024-1, 0, NULL, NULL);
              /*recv((int) arg,recv_data,1024,0);*/
             
              if (bytes_received == -1)
            {
              /*
               * Socket in error state
               */
              perror ("Client recv(): ");
              exit(1);
            }        
         
              printf("\nThe number of digit received: %d\n", bytes_received);
              recv_data[bytes_received] = '\0';

              if (strcmp(recv_data, "q") == 0 || strcmp(recv_data , "Q") == 0)
              {
                send((int) arg, "q", strlen("q"), 0);
//                close((int) arg);
                break;
              }

              else 
              printf("\n RECEIVED DATA = %s \n" , recv_data);
              fflush(stdout);
              }
              
//              if (pthread_cancel (send_thr)!= 0)
//              perror ("Thread cancelation ");              ;              

}[/CODE] 

When i compile this code with the error shown.

shufei@shufei-desktop:~/Desktop$ gcc -lpthread threadclient.c -o threadclient
threadclient.c: In function ‘cthr_send’:
threadclient.c:114: error: ‘recv_thr’ undeclared (first use in this function)
threadclient.c:114: error: (Each undeclared identifier is reported only once
threadclient.c:114: error: for each function it appears in.)

is anyone know why it say the recv_thr is undeclare since it was declared in secondary thread. Please forgive my if this is an stupid question.

Regards,
wssoh