Help solve this program exit problem

Help solve the problem of program exit-Linux general technology-Linux technology and application information. The following is a detailed description. Server:
# Include
# Include
# Include
# Include
# Include
# Include
# Include
# Include
# Include
# Include

# Define MYPORT 4000
# Define BACKLOG 2

Char bye [] = "exit ";

Struct
{
Int sock_fd;
Int client_fd;
Pthread_t sen_tidp;
Pthread_t rev_tidp;
} Pid;

Void * rev_msg (void * arg)
{
Int * sock_fd;
Int num, OK;
Char buf [1024];

Sock_fd = (int *) arg;

Pthread_setcancelstate (PTHREAD_CANCEL_ENABLE, NULL );
Pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, NULL );

OK = 0;
Do
{
Num = read (* sock_fd, buf, 1023 );
Buf [num] = '\ 0 ';
Printf ("it said: % s \ n", buf );
If (strncasecmp (buf, bye, 4) = 0)
OK = 1;
} While (! OK );
Sleep (2 );
Pthread_cancel (pid. sen_tidp );
Return (void *) 0;
}

Void * sent_msg (void * arg)
{
Int * sock_fd;
Int num, OK;
Char buf [1024] = "Welcome! ";

Sock_fd = (int *) arg;
Pthread_setcancelstate (PTHREAD_CANCEL_ENABLE, NULL );
Pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, NULL );

Num = strlen (buf );
Write (* sock_fd, buf, num );
OK = 0;
Do
{
Scanf ("% s", & buf );
Num = strlen (buf );
Write (* sock_fd, buf, num );
If (strncasecmp (buf, bye, 4) = 0)
OK = 1;
} While (! OK );

Sleep (2 );
Pthread_cancel (pid. rev_tidp );
Return (void *) 0;
}

Int main (int argc, char * argv [])
{
Int sock_fd, client_fd;
Int num;
Struct sockaddr_in serv_addr, client_addr;

Pthread_t sen_tidp, rev_tidp;

Serv_addr.sin_family = AF_INET;
Serv_addr.sin_port = htons (MYPORT );
Serv_addr.sin_addr.s_addr = htonl (INADDR_ANY );
Bzero (& (serv_addr.sin_zero), 8 );

Sock_fd = socket (AF_INET, SOCK_STREAM, 0 );
Bind (sock_fd, (struct sockaddr *) & serv_addr, sizeof (struct sockaddr_in ));
Listen (sock_fd, BACKLOG );
Num = sizeof (struct sockaddr_in );
Client_fd = accept (sock_fd, (struct sockaddr *) & client_addr, & num );

Pthread_create (& sen_tidp, NULL, sent_msg, (void *) & client_fd );
Pthread_create (& rev_tidp, NULL, rev_msg, (void *) & client_fd );

Pid. sock_fd = sock_fd;
Pid. client_fd = client_fd;
Pid. sen_tidp = sen_tidp;
Pid. rev_tidp = rev_tidp;

Pthread_join (sen_tidp, NULL );
Pthread_join (rev_tidp, NULL );

Close (client_fd );
Close (sock_fd );
Exit (0 );
}

Client:
# Include
# Include
# Include
# Include
# Include
# Include
# Include
# Include
# Include
# Include

# Define SERV_PORT 4000

Volatile pthread_t rev_tidp, sen_tidp;

Char bye [] = "exit ";

Void * sen_msg (void * arg)
{
Int * sock_fd;
Int num;
Char buf [1024];

Sock_fd = (int *) arg;
Pthread_setcancelstate (PTHREAD_CANCEL_ENABLE, NULL );
Pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, NULL );
Sleep (2 );
Do
{

Scanf ("% s", & buf );

Num = strlen (buf );
Write (* sock_fd, buf, num );
} While (strncasecmp (buf, bye, 4 )! = 0 );
Pthread_cancel (rev_tidp );
Pthread_exit (void *) 0 );
}

Void * rev_msg (void * arg)
{
Int * sock_fd;
Int num;
Char buf [1024];

Sock_fd = (int *) arg;

Pthread_setcancelstate (PTHREAD_CANCEL_ENABLE, NULL );
Pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, NULL );

Do
{
Num = read (* sock_fd, buf, 1023 );
Buf [num] = '\ 0 ';
Printf ("it said: % s \ n", buf );
} While (strncasecmp (buf, bye, 4 )! = 0 );

Sleep (2 );
Pthread_cancel (sen_tidp );
Pthread_exit (void *) 0 );
}

Int main (int argc, char * argv [])
{
Int sock_fd;
Int nbyte, nbyte1, num;
Struct sockaddr_in serv_addr;
Struct hostent * host;

Host = gethostbyname ("localhost ");

Serv_addr.sin_family = AF_INET;
Serv_addr.sin_port = htons (SERV_PORT );
Serv_addr.sin_addr = * (struct in_addr *) host-> h_addr );
Bzero (& (serv_addr.sin_zero), 8 );

Sock_fd = socket (AF_INET, SOCK_STREAM, 0 );
Connect (sock_fd, (struct sockaddr *) & serv_addr, sizeof (struct sockaddr_in ));

Pthread_create (& rev_tidp, NULL, rev_msg, (void *) & sock_fd );
Pthread_create (& sen_tidp, NULL, sen_msg, (void *) & sock_fd );

Pthread_join (rev_tidp, NULL );
Sleep (2 );
Pthread_join (sen_tidp, NULL );


Close (sock_fd );
Exit (0 );
}

Why is a program always unable to exit normally when exiting?