Delay on server side - multithreading

Question

I have a question regarding server - client data transmission. The data is sent by the client after satisfying simple protocol. But I found there is a delay on server side. The client and the server are tested on the same PC that has an i5 core with SSD and 8 GB ram.
The way how I measured the delay is, after the clients says "Sending," both sides write current system time in millisecond. The data itself is the current system time sent by the client. The server is checking how much it is delayed in the server side. It starts from 0 ms and is increased up to 90 ms and stabilized at 40 ms. I wonder this delay is normal.
Here is the code of the server(multi-threaded):
....
while(!ScriptWillAcessHere){
inputLine = in.readLine();
//Greetings
if(i==0)
{
outputLine = SIMONSAYS.processInput(inputLine);
out.println(outputLine);
}
if(inputLine.equals("Sending")){
i = 1;
}
if(i>=1){ //Javascript will access this block
if(i==1){
StartTime = System.currentTimeMillis();
System.out.println(StartTime);
i++;
}
Differences = System.currentTimeMillis() - Double.parseDouble(inputLine);
saveSvr.write(Double.toString(Differences)+"\n");
...
//Checking elapsed time below:
}
}
Here is the code of the client(single thread):
....
if(Client.equals("Sending"))
{
while(bTimer)
{
ins++;
local_time = System.currentTimeMillis();
out.println(local_time);
if(ins >= 100000)
{
out.println("End of Message");
break;
}
}
}
Thanks,

Answer 1

This code must be removed from the while() loop. It causes massive CPU traffic and delay on server side.
Differences = System.currentTimeMillis() - Double.parseDouble(inputLine);
Instead, if anyone needs to compare server side local time with client local time, use ping each other first then save their local time at the beginning of transmission then save both in the server.
If there is no delay in the hub, pinging will indicates Max. 1 ms delay and both local time must be identical.
Of course, the client's local time must be adjusted according to the server time; that's why we need to save their local time at the beginning of the transmission to find an offset.
Also, if the server is doing some different task at the same time, there must be some delay around 10-15 ms. If the transmission itself doesn't have any delay, the Max. delay of this operation must be identical to the server internal delay. I found the server was also running different tasks at the same time and had Max. 15 ms delay caused by them. So, total delay on the server is:
Total delay = server internal delay on other tasks + server internal delay on transmission thread + transmission delay.