Is possible to control the amount of time that each thread executes in Java?

Question

I want to control the amount of time that each thread uses.

One thread does some processing and another processes data in the database, but the insertion is slower than processing because of the amount of generated data. I want to give more processor time to insert that data.

Is it possible do this with threads? At the moment, I'm putting a sleep in the thread doing the processing, but the time of insertion changes according to the machine. Is there another way I can do this? Is the way involving the use of thread synchronization inside my program?

Answer 1

The first thing to mention is that thread priority doesn't per se mean "share of the CPU". There seems to be a lot of confusion about what thread priority actually means, partly because it actually means different things under different OS's. If you're working in Linux, it actually does mean something close to relative share of CPU. But under Windows, it definitely doesn't. So in case it's of any help, you may firstly want to look at some information I compiled a little while ago about thread priorities in Java, which explains what Thread Priorities Actually Mean on different systems.

The general answer to your question is that if you want a thread to take a particular share of CPU, it's better to implicitly do that programmatically: periodically, for each "chunk" of processing, measure how much time elapsed (or how much CPU was used-- they're not strictly speaking the same thing), then sleep an appropriate amount of time so that the processing/sleep ratio comes to roughly the % of processing time you intended.

However, I'm not sure that will actually help your task here.

As I understand, basically you have an insertion task which is the rate determining step. Under average circumstances, it's unlikely that the system is "deliberately dedicating less CPU than it can or needs to" to the thread running that insertion.

So there's probably more mileage in looking at that insertion task and seeing if programmatically you can change how that insertion task functions. For example: can you insert in larger batches? if the insertion process really is CPU bound for some reason (which I am suspicious of), can you multi-thread it? why does your application actually care about waiting for the insertion to finish, and can you change that dependency?

If the insertion is to a standard DB system, I wonder if that insertion is terribly CPU bound anyway?

Answer 2

You can increase the priority of a thread using Thread.setPriority(...) but this is not ideal.

Perhaps you can use some form of blocking queue from the java.util.concurrent package to make one Thread wait while another Thread is doing something. For example, a SynchronousQueue can be used to send a message from one Thread to another Thread that it can now do something.

Another approach is to use Runnables instead of Threads, and submit the Runnables to an Executor, such as ThreadPoolExecutor. This executor will have the role of making sure Runnables are using a fair amount of time.

Answer 3

One way would be to set the priority of the processing thread to be lower than the other. But beware this is not recommended as it wont keep your code platform independent. (DIfferent thread priorities behave differently on different platforms).

Another way would be to use a service where database thread would keep sending messages about its current status (probably some flag "aboutToOver").

Or use synchronization say a binary semaphore. When the database thread is working, the other thread would be blocked and hence db thread would be using all the resources. But again processing thread would be blocked in the mean time. Actually this will be the best solution as the processign thread can perform say 3-4 tasks and then will get blocked by semaphore till later when it can again get up and do task