Android: lightweight means of performing a task on a periodic basis (i.e. polling every 500 milliseconds).

Android: PeriodicExecutor.java

package com.codeswimmer.android.executor;

import java.util.concurrent.Executor;

import android.os.Handler;
import android.os.SystemClock;

public class PeriodicExecutor implements Executor {
    private static final Handler poller = new Handler();
    private Runnable command;
    private long period;
    
    public PeriodicExecutor(long period) {
        this.period = period;
    }
    
    @Override
    public void execute(Runnable command) {
        this.command = command;
        poller.postDelayed(executor, period);
    }

    private final Runnable executor = new Runnable() {
        @Override
        public void run() {
            long uptimeMillis = SystemClock.uptimeMillis();
            command.run();
            poller.postAtTime(this, uptimeMillis + PeriodicExecutor.this.period);
        }
    };
}