java thread day02

java.util.concurrent
public interface ExecutorService
extends Executor
An Executor that provides methods to manage termination and methods that can produce a Future for tracking progress of one or more asynchronous tasks.
An ExecutorService can be shut down, which will cause it to reject new tasks. Two different methods are provided for shutting down an ExecutorService. The shutdown method will allow previously submitted tasks to execute before terminating, while the shutdownNow method prevents waiting tasks from starting and attempts to stop currently executing tasks. Upon termination, an executor has no tasks actively executing, no tasks awaiting execution, and no new tasks can be submitted. An unused ExecutorService should be shut down to allow reclamation of its resources.
Method submit extends base method Executor.execute(Runnable) by creating and returning a Future that can be used to cancel execution and/or wait for completion. Methods invokeAny and invokeAll perform the most commonly useful forms of bulk execution, executing a collection of tasks and then waiting for at least one, or all, to complete. (Class ExecutorCompletionService can be used to write customized variants of these methods.)
The Executors class provides factory methods for the executor services provided in this package.
Usage Examples
Here is a sketch of a network service in which threads in a thread pool service incoming requests. It uses the preconfigured Executors.newFixedThreadPool factory method:
   class NetworkService implements Runnable {
    private final ServerSocket serverSocket;
    private final ExecutorService pool;
 
    public NetworkService(int port, int poolSize)
        throws IOException {
      serverSocket = new ServerSocket(port);
      pool = Executors.newFixedThreadPool(poolSize);
    }
 
    public void run() { // run the service
      try {
        for (;;) {
          pool.execute(new Handler(serverSocket.accept()));
        }
      } catch (IOException ex) {
        pool.shutdown();
      }
    }
  }
 
  class Handler implements Runnable {
    private final Socket socket;
    Handler(Socket socket) { this.socket = socket; }
    public void run() {
      // read and service request on socket
    }
  }
The following method shuts down an ExecutorService in two phases, first by calling shutdown to reject incoming tasks, and then calling shutdownNow, if necessary, to cancel any lingering tasks:
   void shutdownAndAwaitTermination(ExecutorService pool) {
    pool.shutdown(); // Disable new tasks from being submitted
    try {
      // Wait a while for existing tasks to terminate
      if (!pool.awaitTermination(60, TimeUnit.SECONDS)) {
        pool.shutdownNow(); // Cancel currently executing tasks
        // Wait a while for tasks to respond to being cancelled
        if (!pool.awaitTermination(60, TimeUnit.SECONDS))
            System.err.println("Pool did not terminate");
      }
    } catch (InterruptedException ie) {
      // (Re-)Cancel if current thread also interrupted
      pool.shutdownNow();
      // Preserve interrupt status
      Thread.currentThread().interrupt();
    }
  }
Memory consistency effects: Actions in a thread prior to the submission of a Runnable or Callable task to an ExecutorService happen-before any actions taken by that task, which in turn happen-before the result is retrieved via Future.get().
Since:
1.5

java.util.concurrent
public interface Executor
An object that executes submitted Runnable tasks. This interface provides a way of decoupling task submission from the mechanics of how each task will be run, including details of thread use, scheduling, etc. An Executor is normally used instead of explicitly creating threads. For example, rather than invoking new Thread(new(RunnableTask())).start() for each of a set of tasks, you might use:
   Executor executor = anExecutor;
   executor.execute(new RunnableTask1());
   executor.execute(new RunnableTask2());
   ...
   
However, the Executor interface does not strictly require that execution be asynchronous. In the simplest case, an executor can run the submitted task immediately in the caller's thread:
   class DirectExecutor implements Executor {
    public void execute(Runnable r) {
      r.run();
    }
  }
More typically, tasks are executed in some thread other than the caller thread. The executor below spawns a new thread for each task.
   class ThreadPerTaskExecutor implements Executor {
    public void execute(Runnable r) {
      new Thread(r).start();
    }
  }
Many Executor implementations impose some sort of limitation on how and when tasks are scheduled. The executor below serializes the submission of tasks to a second executor, illustrating a composite executor.
   class SerialExecutor implements Executor {
    final Queue<Runnable> tasks = new ArrayDeque<Runnable>();
    final Executor executor;
    Runnable active;
 
    SerialExecutor(Executor executor) {
      this.executor = executor;
    }
 
    public synchronized void execute(final Runnable r) {
      tasks.offer(new Runnable() {
        public void run() {
          try {
            r.run();
          } finally {
            scheduleNext();
          }
        }
      });
      if (active == null) {
        scheduleNext();
      }
    }
 
    protected synchronized void scheduleNext() {
      if ((active = tasks.poll()) != null) {
        executor.execute(active);
      }
    }
  }
The Executor implementations provided in this package implement ExecutorService, which is a more extensive interface. The ThreadPoolExecutor class provides an extensible thread pool implementation. The Executors class provides convenient factory methods for these Executors.
Memory consistency effects: Actions in a thread prior to submitting a Runnable object to an Executor happen-before its execution begins, perhaps in another thread.
Since:
1.5