I thought that using ThreadPoolExecutor we can submit Runnables to be executed either in the BlockingQueue passed in the constructor or using the execute method.
Also my understanding was that if a task is available it will be executed.
What I don't understand is the following:
public class MyThreadPoolExecutor {
private static ThreadPoolExecutor executor;
public MyThreadPoolExecutor(int min, int max, int idleTime, BlockingQueue<Runnable> queue){
executor = new ThreadPoolExecutor(min, max, 10, TimeUnit.MINUTES, queue);
//executor.prestartAllCoreThreads();
}
public static void main(String[] main){
BlockingQueue<Runnable> q = new LinkedBlockingQueue<Runnable>();
final String[] names = {"A","B","C","D","E","F"};
for(int i = 0; i < names.length; i++){
final int j = i;
q.add(new Runnable() {
@Override
public void run() {
System.out.println("Hi "+ names[j]);
}
});
}
new MyThreadPoolExecutor(10, 20, 1, q);
try {
TimeUnit.SECONDS.sleep(5);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
/*executor.execute(new Runnable() {
@Override
public void run() {
System.out.println("++++++++++++++");
}
}); */
for(int i = 0; i < 100; i++){
final int j = i;
q.add(new Runnable() {
@Override
public void run() {
System.out.println("Hi "+ j);
}
});
}
}
}
This code does not do absolutely anything unless I either uncomment the executor.prestartAllCoreThreads(); in the constructor OR I call execute of the runnable that prints System.out.println("++++++++++++++"); (it is also commented out).
Why?
Quote (my emphasis):
By default, even core threads are initially created and started only when new tasks arrive, but this can be overridden dynamically using method prestartCoreThread() or prestartAllCoreThreads(). You probably want to prestart threads if you construct the pool with a non-empty queue.
Ok. So my queue is not empty. But I create the executor, I do sleep and then I add new Runnables to the queue (in the loop to 100).
Doesn't this loop count as new tasks arrive?
Why doesn't it work and I have to either prestart or explicitely call execute?