How to catch all udp messages like Wireshark without drops? - c

Question

I have two programs udp sender and consumer on localhost. Sender generates four byte int messages at top speed, but the consumer does not get all of them. Consumer last line on stdout is
1484444 1999999
Wireshark intercepts all packages and slowly processes them all. How can I get the same behavior in a C program?
// sender.c
#include <sys/socket.h>
#include <netinet/in.h>
#include <strings.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <string.h>
int main()
{
int sock = socket(AF_INET, SOCK_DGRAM, 0);
struct sockaddr_in dest;
bzero(&dest, sizeof(dest));
dest.sin_family = AF_INET;
dest.sin_port = htons(40500);
inet_aton("127.0.0.1", &dest.sin_addr);
int i;
for (i = 0; i < 2000000; ++i) {
sendto(sock, &i, sizeof(i), 0, (const struct sockaddr*)&dest, sizeof(dest));
}
}
// consumer.c
#include <sys/socket.h>
#include <netinet/in.h>
#include <strings.h>
#include <arpa/inet.h>
#include <stdio.h>
int main()
{
int sock = socket(AF_INET, SOCK_DGRAM, 0);
struct sockaddr_in dest;
bzero(&dest, sizeof(dest));
dest.sin_family = AF_INET;
dest.sin_port = htons(40500);
inet_aton("127.0.0.1", &dest.sin_addr);
bind(sock, (const struct sockaddr*)&dest, sizeof(dest));
int i;
int buf;
for (i = 0; i < 2000000; ++i) {
recv(sock, &buf, sizeof(buf), 0);
printf("%d %d\n", i, buf);
}
}

Answer 1

I think your problem is the server side process slower than the
sender side.If the receive socket buffer of the server is full,
then the extra packets delivered by the kernel will be droped.
To improve the performance, I think there are several things you
can do:
1.Increase the server side receive buffer.
2.Try use batch send and receive interfaces(eg. sendmmsg(), recvmmsg()).
This will reduce the overhead of system call.
3.Don't call printf() everytime you receive a buffer of data.
It is time consuming.