Re: How hard is socket programming?
Joseph M. Newcomer wrote:
No, a recv() is a loop and you read 8K at a time:
****
Note that you read AT MOST 8K, and that's because of the sizeof(buf) parameter to the recv
being 8*1024. If you made it 16*1024, you might receive up to 16K at a time, but in all
cases, this is the MAXIMUM that will be returned; you might get fewer bytes, based on
network traffic and your sender and receiver stacks.
Joe, the reason 8K is used is because by default the winsock stack
packet size is set to 8K.
So in practice, it is better to keep it aligned with the what the
socket has otherwise you can run into pressure points and bucket
brigade situations.
You can get/set change socket send/recv sizes as show with the example
below. 8K is the default. But in principle, not only is stack is set
to a certain size, the stacks at nodes in between END POINTS are set
as well too. You need to look for bucket brigade scenarios where you
sending 32K packet sizes, but the receiver is still at 8K, that means
it has I/O Pending at least 4 times.
Overall, in communications whether for RS232, sockets, etc, the rule
of thumb for data transfer efficiency is:
- SEND LOW
- RECEIVE HIGH
The sender does not know what a receiver can handle, so you don't want
to over pressure it. However, a receiver knows what it can handle so
it should be ready to receive as much it can. If your communication
products deviates from this, you will see inefficient data transfer
scenarios.
// File: testwinsock1.cpp
// compile: cl testwinsock1.cpp
#include <windows.h>
#include <stdio.h>
#include <winsock.h>
#include <conio.h>
#pragma comment(lib,"wsock32.lib")
int main(char argc, char *argv[])
{
WSADATA wd;
int size;
int n;
if (WSAStartup(MAKEWORD(1, 1), &wd) != 0) {
return 1;
}
SOCKET sock = socket(PF_INET, SOCK_STREAM, 0);
n = sizeof(int);
getsockopt(sock, SOL_SOCKET,SO_SNDBUF,(char *)&size,&n);
printf("SO_SNDBUF: %d\n",size);
n = sizeof(int);
getsockopt(sock,SOL_SOCKET,SO_RCVBUF,(char *)&size,&n);
printf("SO_RCVBUF: %d\n",size);
closesocket(sock);
return 0;
}
Output:
SO_SNDBUF: 8192
SO_RCVBUF: 8192
--
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