Java reduce CPU usage

Question

Greets-

We gots a few nutters in work who enjoy using

while(true) { //Code } 

in their code. As you can imagine this maxes out the CPU. Does anyone know ways to reduce the CPU utilization so that other people can use the server as well.

The code itself is just constantly polling the internet for updates on sites. Therefore I'd imagine a little sleep method would greatly reduce the the CPU usage.

Also all manipulation is being done in String objects (Java) anyone know how much StringBuilders would reduce the over head by?

Thanks for any pointers

Answer 1

A lot of the "folk wisdom" about StringBuilder is incorrect. For example, changing this:

String s = s1 + ":" + s2 + ":" + s3;

to this:

StringBuilder sb = new StringBuilder(s1);
sb.append(":");
sb.append(s2);
sb.append(":");
sb.append(s3);
String s = sb.toString();

probably won't make it go any faster. This is because the Java compiler actually translates the concatenation sequence into an equivalent sequence of appends to a temporary StringBuilder. Unless you are concatenating Strings in a loop, you are better of just using the + operator. Your code will be easier to read.

The other point that should be made is that you should use a profiler to identify the places in your code that would benefit from work to improve performance. Most developers' intuition about what is worth optimizing is not that reliable.

Answer 2

I'll start off with your second question, I would like to agree with the rest that StringBuilder vs String is very much dependent on the particular string manipulations. I had "benchmarked" this once and generally speaking as the amount of new string allocations went up (usually in the form of concatenations) the overall execution time went up. I won't go into the details and just say that StringBuilder turned out to be most efficient overtime, when compared to String, StringBuffer, String.format(), MessageFormat...

My rule of thumb is that whenever I wish to concatenate more than 3 string together I always use StringBuilder.

As for your first question. We had a requirement to bring CPU usage to 5%. Not an easy task. We used Spring's AOP mechanism to add a Thread.sleep() to before any method execution of a CPU intensive method. The Thread.sleep() would get invoked only if some limit had been exceeded. I am sorry to say that the computation of this limit is not that simple. And even sorrier to say that I still have not obtained the permission to post it up on the net. So this is just in order to put you on an interesting but complicated track that has proven to work over time.

Answer 3

How often do those sites update? You're probably really annoying the hosts. Just stick a Thread.sleep(60 * 1000); at the end of the loop and you can avoid this. That'll poll them once a minute—surely that's enough?