metodo newFixedThreadPool
Un pool di thread fisso può essere ottenuto chiamando il metodo statico newFixedThreadPool () della classe Executors.
Sintassi
ExecutorService fixedPool = Executors.newFixedThreadPool(2);
dove
Saranno attivi massimo 2 thread per elaborare le attività.
Se vengono inviati più di 2 thread, vengono tenuti in coda fino a quando i thread non diventano disponibili.
Viene creato un nuovo thread per sostituirlo se un thread termina a causa di un errore durante l'esecuzione, l'arresto dell'esecutore non è ancora stato chiamato.
Qualsiasi thread esiste fino all'arresto del pool.
Esempio
Il seguente programma TestThread mostra l'utilizzo del metodo newFixedThreadPool in un ambiente basato su thread.
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
public class TestThread {
public static void main(final String[] arguments) throws InterruptedException {
ExecutorService executor = Executors.newFixedThreadPool(2);
// Cast the object to its class type
ThreadPoolExecutor pool = (ThreadPoolExecutor) executor;
//Stats before tasks execution
System.out.println("Largest executions: "
+ pool.getLargestPoolSize());
System.out.println("Maximum allowed threads: "
+ pool.getMaximumPoolSize());
System.out.println("Current threads in pool: "
+ pool.getPoolSize());
System.out.println("Currently executing threads: "
+ pool.getActiveCount());
System.out.println("Total number of threads(ever scheduled): "
+ pool.getTaskCount());
executor.submit(new Task());
executor.submit(new Task());
//Stats after tasks execution
System.out.println("Core threads: " + pool.getCorePoolSize());
System.out.println("Largest executions: "
+ pool.getLargestPoolSize());
System.out.println("Maximum allowed threads: "
+ pool.getMaximumPoolSize());
System.out.println("Current threads in pool: "
+ pool.getPoolSize());
System.out.println("Currently executing threads: "
+ pool.getActiveCount());
System.out.println("Total number of threads(ever scheduled): "
+ pool.getTaskCount());
executor.shutdown();
}
static class Task implements Runnable {
public void run() {
try {
Long duration = (long) (Math.random() * 5);
System.out.println("Running Task! Thread Name: " +
Thread.currentThread().getName());
TimeUnit.SECONDS.sleep(duration);
System.out.println("Task Completed! Thread Name: " +
Thread.currentThread().getName());
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
Questo produrrà il seguente risultato.
Produzione
Largest executions: 0
Maximum allowed threads: 2
Current threads in pool: 0
Currently executing threads: 0
Total number of threads(ever scheduled): 0
Core threads: 2
Largest executions: 2
Maximum allowed threads: 2
Current threads in pool: 2
Currently executing threads: 1
Total number of threads(ever scheduled): 2
Running Task! Thread Name: pool-1-thread-1
Running Task! Thread Name: pool-1-thread-2
Task Completed! Thread Name: pool-1-thread-2
Task Completed! Thread Name: pool-1-thread-1