Windows posix sockets performance

I am looking for information on Windows network programm开发者_C百科ing. Mainly how to get a single executable to cope with 1000 connections.

We use select() FD_ISSET etc on unix and this works very quick. On Windows these APIs are very poor. FD_SET is lots slower but even when working around this, Windows is lots slower than HPUX.

I'm looking for a win32 API call which I can use instead of the select() call which doesnt require so much CPU/time. Currently we spend 50% of the time (and CPU) in select(), where as on unix the time spent in send() and recv(), which is what I would expect.

Thanks Neil

You are probably looking for Windows I/O Completion Ports. Here's an article from SysInternals guys.

If you are really into the scalable sockets programming, nothing would outperform IO completion ports on Windows.

Having said this, you program would likely need a big rewrite for completion ports model.

However, it is possible to improve performance even with select()/FD_ISSET.

Here is how it can be done: in winsock2.h fd_set is defined as an array of SOCKETs and a element counter

typedef struct fd_set {
    u_int fd_count;               /* how many are SET? */
    SOCKET  fd_array[FD_SETSIZE];   /* an array of SOCKETs */
} fd_set;

Also in winsock2.h you'll find that FD_SET adds a SOCKET at the end of this array, and FD_ISSET is doing a linear search in the array.

Now if you change macros to use sorted array of SOCKETs, i.e

• FD_SET adds sockets in the sorted order
• FD_ISSET does binary search instead of linear

then dependent on the size of the array FD_ISSET can be greatly improved (while performance of FD_SET will degrade somewhat, but we're assuming that FD_SET is a seldom operation).

On Unixes, performance of select() is better since they FD_SET as bitmap, FD_SET/FD_ISSET would just test or set a bit. On Windows this technique would not be applicable because socket is not a small positive file descriptor number, it is a HANDLE and scalar value of a handle can be large.