java udp server 100% cpu

Question

I have a UDP server that receives packets at 40 pkts per seconds. The main loop is below:

 public void serve() {
        while(true) {
              ByteBuffer bytes = ByteBuffer.allocate(1024);
              bytes.clear();
              channel.receive(bytes);
              THandler th = new THandler(bytes);
              th.start();
        }
    }

Channel Initialization:

private final DatagramChannel channel ;  
channel = DatagramChannel.open();
channel.socket().bind(new InetSocketAddress(port));

The class THandler extends a thread class and it filters the message against a regular expression and then finds an id from the matching message. This id is then compared to a list of subscribers (approx 300k). followed by a db select followed by an update.

public void run() {

    if (!this.isValidLog()){ //does a regular expression match
        return;
    }
    String subsId = this.getSubscriberId(); // extracts the id from message
    if (this.isServiceSubscribed(subsId)) { // compares in a list of subscribers

        usageDetails = this.getServiceUsage(subsId); // db Query
        if(usageDetails.isFeatureAvailable()){
            usageDetails.updateUsageCounter(); // db Update
        }
    }


}

I have tried using ExecutorService also. But the problem is that I run out of CPU time with 99.6% or more in user.

Any inputs on how to improve the performance of the server and code are most welcome.

It doesn't look like a matter of performance, while(true) { is a busy loop that will indeed eat up 100% of a cpu if there is nothing in there that will put the logic to rest for a period of time. As a test, try adding a Thread.sleep(1) in that busy loop to see how that influences the CPU usage. — Gimby, Feb 01 '16 at 11:35
It seems like you need to profile your code. This can be done with `jvisualvm` that comes with your JDK. @EJP has a great answer otherwise — Steve C, Feb 01 '16 at 12:02
I suggest you use a cached Thread Pool i.e. ExecutorService instead of creating a Thread for each packet. Creating a Thread is very expensive, and you might find the pool is rarely more than one thread in it. — Peter Lawrey, Feb 01 '16 at 13:50
You only need to clear a ByteBuffer if you are re-using it. A new ByteBuffer is always `clear()` — Peter Lawrey, Feb 01 '16 at 13:51

score 2 · Accepted Answer · answered Feb 01 '16 at 11:50

Make sure the channel is in blocking mode.
You don't need to clear a newly created ByteBuffer.
Use an ExecutorService with a reasonably sized thread pool, instead of creating a new thread per datagram.
Ensure you are using O(1) data structures.
Combine the database lookup and update into one operation, using UPDATE ... WHERE, and get the update count if you need to see whether anything happened.
Ignore any suggestion to add sleeps into networking code. They are literally a waste of time.

score 0 · Answer 2 · answered Feb 01 '16 at 11:36

0

Most likely your search is simply iteration through an array. You might want to replace these with a more efficient method.

Have a look at the Map specially HashMap and TreeMap

answered Feb 01 '16 at 11:36

Dawnkeeper

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I tried by pruning the list to only one subscriber, but to no avail, CPU still 100% occupied. – friedFingers Feb 01 '16 at 11:39
In that case the DatagramChannel might not be in blocking mode as @EJP mentioned is his answer. My suspicion was that the data handling/searching took up all the CPU. – Dawnkeeper Feb 01 '16 at 12:11

java udp server 100% cpu

2 Answers2