After each sending data packet, I add Thread.sleep(1), why does the packet loss rate of udp drop? - udp

Question

Udp server
#include <unistd.h>
#include <stdio.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#define PORT 10086
int main() {
int server_fd = socket(AF_INET, SOCK_DGRAM, 0);
if (server_fd < 0) {
perror("create socket");
_exit(2);
}
int ret;
struct sockaddr_in s_addr;
s_addr.sin_family = AF_INET;
s_addr.sin_addr.s_addr = htonl(INADDR_ANY);
s_addr.sin_port = htons(PORT);
ret = bind(server_fd, (struct sockaddr *) &s_addr, sizeof(s_addr));
if (ret < 0) {
perror("bind error");
_exit(2);
}
for (;;) {
struct sockaddr_in c_addr;
socklen_t c_addr_len;
char buf[100];
int ret = recvfrom(server_fd, buf, 100, 0, (struct sockaddr *) &c_addr, &c_addr_len);
if (ret < 0) {
perror("accept error");
_exit(2);
} else {
char temp[100];
char *host2 = inet_ntoa(c_addr.sin_addr);
printf("A client connect: %d, %s, %d with msg: %s.\n", c_addr.sin_port, host2, c_addr.sin_family, buf);
}
}
}
Server listen on 10086, recvfrom a udp data packet, print client IP, port and data.
And here is client code:
public static void main(String[] args) throws IOException {
String server = "192.168.1.5";
DatagramSocket ds = new DatagramSocket();
byte[] data = "Hello".getBytes();
DatagramPacket p = new DatagramPacket(data, data.length);
p.setAddress(InetAddress.getByName(server));
p.setPort(10086);
ds.send(p);
data = "world".getBytes();
p = new DatagramPacket(data, data.length);
p.setAddress(InetAddress.getByName(server));
p.setPort(10086);
ds.send(p);
}
After run client, I get server output(tested several times, same output)
A client connect: 38394, 192.168.1.2, 2 with msg: Hello.
After I add Thread.sleep(1); after send "Hello" to server.
public static void main(String[] args) throws IOException, InterruptedException {
DatagramSocket ds = new DatagramSocket();
byte[] data = "Hello".getBytes();
DatagramPacket p = new DatagramPacket(data, data.length);
String server = "192.168.1.5";
p.setAddress(InetAddress.getByName(server));
p.setPort(10086);
ds.send(p);
Thread.sleep(1);
data = "world".getBytes();
p = new DatagramPacket(data, data.length);
p.setAddress(InetAddress.getByName(server));
p.setPort(10086);
ds.send(p);
}
After run client, I get server output(tested several times, same output)
A client connect: 38394, 192.168.1.2, 2 with msg: Hello.
A client connect: 38394, 192.168.1.2, 2 with msg: world.
I checked it with Wireshark and it's OK.
I also checked socket read buffer and it's OK.
So why is there packet loss here? There should be no buffer overflow, and the network environment is not that bad. Is there any other reason for UDP packet loss?
Thanks in advance.