Question

I’m trying to setup a concurrency structure where some boiler plate code should be executed (to check pre-conditions) before a certain type of task. In other words, I would like to run code after an Executor has dequeued a task, but before it invokes execute on it. How can this be done?

Answer 1

Use a decorator?

public class TestExecutor{
    public static void main(String[] args){
        Executor e = Executors.newCachedThreadPool();
        e = new PreconditionCheckerExecutor(e){
            @Override
            protected void checkPrecondition(Runnable command){
                //do some precondition
            }
        };
        e.execute(/*myRunnable1*/);
        e.execute(/*myRunnable2*/);

    }
}
abstract class PreconditionCheckerExecutor implements Executor
{
    private final Executor executor;

    PreconditionCheckerExecutor(Executor executor) {
        this.executor = executor;
    }

    @Override
    public void execute(Runnable command) {
        checkPrecondition(command);
        executor.execute(command);
    }

    protected abstract void checkPrecondition(Runnable command);
}

You can make it more specific if you want (eg by replacing Executor by ExecutorService) depending on your needs.