Please help! accept function problems in Socket programming

Hi,

I have a client-server socket program. It has been working fine for over a year, but recently it started to show strange behavior.
After the server program runs for a while, it will show in the top command saying it is using lots of CPU, MEM. I assume it means the server code is processing some requests. But I never sent a request from the client side(from a web page). When this happens, I try to send a request to the server, the server won't response. I looked at the output from the server side, it shows the accept was called before, though I didn't send any connect calls from the client. I guess the server stopped at the read().
Parts of the program is:

void CServer_pth::run_pth(Nabor_pth *Nab, Bool_pth *Bl, BnBayes_pth *Bnb, Focus_pth *Foc, Slice_Accpth *Sac) {

int i, nsid;

pNab = Nab;
pBl = Bl;
pBnb = Bnb;
pFoc = Foc;
pSac = Sac;

//create a stream socket
// Sock sp(AF_INET, SOCK_STREAM, 0);
if (!sp.good()) {
cout<<"sp.good() failed\n";
exit(1);
}

//Bind a name to the server socket
if (sp.bind(host, port) < 0) {
cout<<"sp.bind failed\n";
sp.~Sock();
exit(2);
}

for (i=0; i<NUM_THR; i++) {
if (pthread_create(&srvtid[i], &thread_attr, commsrv_pth,tdata[i])) {
perror("pthread_create");
cout<<"srvtid[i], i="<<i<<endl;
cout<<"error in pthread_create, in commsrv_pth\n";
exit(1);
}
}

sem_init(&smp,0, NUM_THR);

for (;;) { //this is a infinite loop, I don't see the option to turn the smile face off

sem_wait(&smp);
while ((nsid = sp.accept(0, 0)) < 0) {
cout<<"accept failed\n";
exit(1);
}

bot = bot%NUM_THR;
i = mat[bot];
cout<<"i in nsid ----> "<<i<<"\tnsid ---> "<<nsid<<endl;
*tdata[i] = nsid;
bot++;

pthread_mutex_lock(&mthread);
pthread_cond_signal(&cond);
pthread_mutex_unlock(&mthread);

}
}

extern "C" void *commsrv_pth(void *argp) {

cmd_Query cmd;
int i, t_nsid;

while (1) {

pthread_mutex_lock(&mthread);
pthread_cond_wait(&cond, &mthread);
pthread_mutex_unlock(&mthread);

pthread_mutex_lock(&mbotp);
botp = botp%NUM_THR;
i = mat[botp];
t_nsid = *tdata[i];
botp++;
pthread_mutex_unlock(&mbotp);

cout<<"i in nsid ----> "<<i<<"\tnsid ---> "<<t_nsid<<endl;
cout<<"wait to read MSG from a client socket\n";

// read MSG1 from a client socket
if (sp.read((char*)&cmd, sizeof(cmd_Query), 0,t_nsid) < 0) {
cout<<"failed in read\n";
return (int*)5;
}
cout<<"after waiting to read\n";

cmd = (cmd_Query)ntohl(cmd);
dispatch_pth(cmd, t_nsid);

close(t_nsid);

pthread_mutex_lock(&mtop);
top = top%NUM_THR;
mat[top] = i;
top++;
pthread_mutex_unlock(&mtop);

sem_post(&smp);
}
return NULL;

}

The above is creating 5(NUM_THR) threads first, then wait the call from clients. I also tried another way which is createing one thread at a time when there's a call from the client. But the same strange behaviour happeded.
void CServer_pth::run_pth(Nabor_pth *pNab, Bool_pth *pBl, BnBayes_pth *pBnb, Focus_pth *pFoc, Slice_Accpth *pSac) {

int i, nsid;

//create a stream socket
Sock sp(AF_INET, SOCK_STREAM, 0);
if (!sp.good()) {
cout<<"sp.good() failed\n";
//return 1;
}

//Bind a name to the server socket
if (sp.bind(host, port) < 0) {
cout<<"sp.bind failed\n";
//return 2;
}

for (i=0; i<NUM_THR; i++) {
tdata[i] = new Thrdata_pth(sp, pNab, pBl, pBnb, pFoc, pSac, i); }

sem_init(&smp,0, NUM_THR);

for (;;) { //this is a infinite loop, I don't see the option to turn the smile face off
while ((nsid = sp.accept(0, 0)) < 0) {
cout<<"accept failed\n";
//return 1;
}

sem_wait(&smp);

bot = bot%NUM_THR;
i = mat[bot];
cout<<"i in nsid ----> "<<i<<"\tnsid ---> "<<nsid<<endl;
tdata[i]->set_nsid(nsid);
if (pthread_create(&srvtid[i], &thread_attr, commsrv_pth,tdata[i])) {
perror("pthread_create");
cout<<"srvtid[i], i="<<i<<endl;
cout<<"error in pthread_create, in commsrv_pth\n";
exit(1);
}
bot++;
}
}

extern "C" void *commsrv_pth(void *argp) {

Thrdata_pth *data = (Thrdata_pth*)argp;
cmd_Query cmd;

cout<<"waiting for reading cmd_Query from a client\n";

// read MSG1 from a client socket
if ((data->t_sp).read((char*)&cmd, sizeof(cmd_Query), 0,data->t_nsid) < 0) {
cout<<"failed in read\n";
return (int*)5;
}

cmd = (cmd_Query)ntohl(cmd);
dispatch_pth(cmd, data);

close(data->t_nsid);

pthread_mutex_lock(&mtop);
top = top%NUM_THR;
mat[top] = data->iz;
top++;
pthread_mutex_unlock(&mtop);

sem_post(&smp);
return NULL;

}

Any advice? Thanks very much for help!!!