Differences

This shows you the differences between two versions of the page.

--- java_concurrency [2012/09/05 10:42]
hkoller [Waiting until tasks are done]
+++ java_concurrency [2012/09/19 17:02] (current)
hkoller [Example: Thread Pool]
@@ Line 1: / Line 1: @@
+====== Basics ======
+  * Thread should be seen as **deprecated**
+====== Executor Framework ======
+Java introduces the [[http://docs.oracle.com/javase/tutorial/essential/concurrency/executors.html|Executor Framework]] as a new Highlevel Mechanism to handle concurrency.
+Basically this includes the following steps:
+  * Create a Worker classes that either implements Runnable or Callable
+  * Create Worker instances
+  * Create an ExecutorService
+    * newSingleThreadExecutor
+    * newCachedThreadPool
+    * newFixedThreadPool
+  * Submit the workers to the executor service
+  * Wait for the workers to finish
+  * Shutdown the ExecutorService
+===== Example: Thread Pool =====
+<code java>
+public class ThreadPoolExecutorDemo {
+	public static void main(String[] args) throws Exception {
+		ExecutorService executor = Executors.newFixedThreadPool(2);
+		executor.submit(new Worker());
+		executor.submit(new Worker());
+		executor.shutdown();
+                executor.awaitTermination(60, TimeUnit.SECONDS); // wait until finished, but at most for 60 seconds
+		System.out.println("Done");
+	}
+	public static class Worker implements Runnable {
+		@Override
+		public void run() {
+		        // do work
+		}
+	}
+}
+</code>
+If the Worker should yield a result, implement **Callable<T>** instead of Runnable:
+<code java>
+public class ThreadPoolTest {
+	public static void main(String[] args) throws Exception {
+		ExecutorService executor = Executors.newFixedThreadPool(2);
+		Future<Integer> result1 = executor.submit(new Worker());
+		Future<Integer> result2 = executor.submit(new Worker());
+		System.out.println("Results: " + result1.get() + " "  result2.get()); // note that get() might throw an Exception if the worker did not finish normally
+	}
+	public static class Worker implements Callable<Integer> {
+		@Override
+		public Integer call() {
+                        int result=0;
+                        // do some work
+			return result;
+		}
+	}
+}
+</code>
+===== Waiting until tasks are done =====
+<code java>
+public static void main(String[] args) throws Exception {
+  List<Worker> tasks = new ArrayList<>();
+  tasks.add(new Worker());
+  tasks.add(new Worker());
+  ExecutorService executor = Executors.newFixedThreadPool(2);
+  List<Future<Integer>> results = executor.invokeAll(tasks); // blocks until all tasks are done
+  System.out.println("Result1: " + results.get(0).get());
+  System.out.println("Result2: " + results.get(1).get());
+  System.out.println("Done");
+  executor.shutdown();
+}
+public static class Worker implements Callable<Integer> {
+.....
+}
+</code>

Small heaps of code

User Tools

Site Tools

Differences

Page Tools