for(i=0;i<=maxDescriptor;i++)
{
if(FD_ISSET(i,&BackUpfdread))



This doesn't work well at all in Windows. sockets are handles, which can have very high values. "maxDescriptor" is ignored on input. You should test the values you know you have (the listening socket, and each client socket) rather than "all integers." You're basically testing ALMOST ALL INTEGERS to see if one of them happens to match a handle value stored in the FD_SET. That is one cause of performance problems.
[/quote]

I had something like that and changed it to as follows. I didn't do any measurements, but thought there was a noticeable improvement in the performance from the change. I count down rather than starting at zero and counting up. Also the code with the selrc is used to shorten this potentially long loop. selrc is the return code from select. After addressing all of the events, we can skip the rest of the loop.


for (int32_t sock = fdmax; sock > 0; --sock) {
if (FD_ISSET(sock, &read_fds)) {
if (mediateRequest(sock)) {
FD_SET(cmwSendbuf.sock_, &masterwrite);
} else {
closeSocket(sock);
FD_CLR(sock, &master);
}
if (0 == --selrc) break;
}
}



Brian Wood
Ebenezer Enterprises
http://webEbenezer.net

[quote name='netpumber' timestamp='1324641936' post='4896797']
Finally i want you to tell me why to use select() and not WSAEventSelect method.
As i read on net the first one uses more CPU than the other.

[quote name='hplus0603' timestamp='1324602493' post='4896692']


for(i=0;i<=maxDescriptor;i++)
{
if(FD_ISSET(i,&BackUpfdread))



This doesn't work well at all in Windows. sockets are handles, which can have very high values. "maxDescriptor" is ignored on input. You should test the values you know you have (the listening socket, and each client socket) rather than "all integers." You're basically testing ALMOST ALL INTEGERS to see if one of them happens to match a handle value stored in the FD_SET. That is one cause of performance problems.
[/quote]I had something like that and changed it to as follows. I didn't do any measurements, but thought there was a noticeable improvement in the performance from the change.

for (int32_t sock = fdmax; sock > 0; --sock) {
if (FD_ISSET(sock, &read_fds)) {

[/quote]
That suffers from exactly the same problem.

You are not iterating over your handles in either examples.

Instead you are iterating over potentially billions of integers where by brute force it will eventually stumble over your handle.


Keep a separate list of handles and only iterate over those. For example, you may have:


typedef std::vector<int32_t> HandleCollection;
...
HandleCollection openHandles;
...

// add an incoming connection
AcceptSocket = accept(ListeningSocket,(SOCKADDR *)&ClientAddr,&ClientAddrSize);
openHandles.push_back(AcceptSocket);
...
for(HandleCollection::iterator it = openHandles.begin(); it!=openhandles.end(); ++it;)
{
if (FD_ISSET(*it, &read_fds)) {
...

This will reduce it from attempting to check against potentially billions of non-handles to instead just checking against the small number of actual handles you know to be open.

In practice you will likely want to store more than just an integer. Eventually you will want a structure or class with additional information about each client, but that is a future exercise.