Our system is having a server and multiple clients. We are monitoring the client FDs using select() system call in HP-UX.

After establishing connection-using socket with the remote client, before start sending the data we are checking the status of socket using select( ) call. For first 16 clients the select() call is unblocked and FD_ISSET( ) returns success. But from the 17th client onwards, the select() is unblocked and FD_ISSET( ) is NOT RETURNING SUCCESS(it is returning negative value), both in HP-UX 11 and 11i. But the same logic works fine till 1024 clients in Solaris, AIX, Linux.
Source code is mentioned below,

Please tell how to rectify this problem.

fd_set Writefds;
struct timeval Timeout;
int RetCode;
int RetValue;
int SockDesc;
struct sockaddr_in client;
char BulkData[5000] = "Acknowledgement";
int retVal;

int clientlen = sizeof( struct sockaddr_in);

client.sin_family = AF_INET;
client.sin_addr.s_addr = INADDR_ANY;
client.sin_port = htons(SERVER_PORT);
SockDesc = socket(AF_INET, SOCK_STREAM, 0);
connect(SockDesc, &client,(socklen_t) clientlen);

Timeout.tv_sec = 0;
Timeout.tv_usec = 0;
FD_ZERO(&Writefds);
FD_SET(SockDesc, &Writefds);
RetCode = select(0, NULL, &Writefds, NULL, &Timeout);
if (RetCode > 0)
{
retVal = FD_ISSET(SockDesc, &Writefds);
if ( retVal > 0)
{
send(SockDesc, szBulkData,(size_t) sizeof(szBulkData), 0);
}
else
{
printf("FD_ISSET is failed:%d\n", retVal);
}
}
else if (RetCode == -1)
{
printf("select return Error:%d\n", errno);
}
else if (RetCode == 0)
{
printf("select return 0 [timeout occured].\n");
}