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Callable
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Callable †

Java 5 から、別スレッドで実行した結果を返せるようになった

package sandbox;

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;
import java.util.logging.Level;
import java.util.logging.Logger;

public class Main2 {

    public static void main(String[] args) {
        FutureTask<String> future = new FutureTask(new Callable<String>() {
            @Override
            public String call() throws Exception {
                return Thread.currentThread().getName();
            }
        });

        new Thread(future).start();
        
        try {
            System.out.println(future.get());
        } catch (InterruptedException ex) {
            Logger.getLogger(Main2.class.getName()).log(Level.SEVERE, null, ex);
        } catch (ExecutionException ex) {
            Logger.getLogger(Main2.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
}

future.get() の引数にタイムアウトを設定できる

        try {
            System.out.println(future.get(2L, TimeUnit.SECONDS));
        } catch (InterruptedException ex) {
            Logger.getLogger(Main2.class.getName()).log(Level.SEVERE, null, ex);
        } catch (ExecutionException ex) {
            Logger.getLogger(Main2.class.getName()).log(Level.SEVERE, null, ex);
        } catch (TimeoutException ex) {
            Logger.getLogger(Main2.class.getName()).log(Level.SEVERE, null, ex);
        }

タイムアウトが起きると TimeoutException? が発生する

Runnable も返値なしの Callable として同じように扱える。

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Thread Pool †

package sandbox;

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;
import java.util.concurrent.SynchronousQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.logging.Level;
import java.util.logging.Logger;

public class Main {

    public static void main(String[] args) {
        try {
            ExecutorService thPool
                    = new ThreadPoolExecutor(
                        0, Integer.MAX_VALUE,
                        30L, TimeUnit.SECONDS,
                        new SynchronousQueue());

            Future<String> future = thPool.submit(new Callable<String>() {

                @Override
                public String call() throws Exception {
                    return Thread.currentThread().getName();
                }
            });
            System.out.println("MAIN:" + Thread.currentThread().getName());
            System.out.println("SUB :" + future.get());

            thPool.shutdown();
        } catch (InterruptedException ex) {
            Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
        } catch (ExecutionException ex) {
            Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
}

ThreadPoolExecutor? のコンストラクタのひな形が用意されている
- ExecutorService? Executors.newSingleThreadExecutor?()
  - new ThreadPoolExecutor?(0, 1, 0L, TimeUnit?.SECONDS, new SynchronousQueue?());
- ExecutorService? Executors.newFixedThreadPool?(int nThreads)
  - new ThreadPoolExecutor?(nThread, nThread, 0L, TimeUnit?.SECONDS, new SynchronousQueue?());
- ExecutorService? Executors.newCachedThreadPool?()
  - new ThreadPoolExecutor?(0, Integer.MAX_VALUE, 60L, TimeUnit?.SECONDS, new SynchronousQueue?());
thPool.shutdown() をして、プールしているスレッドを終わらせないとアプリが終わらない
- shutdown() あり
```
run:
MAIN:main
SUB :pool-1-thread-1
構築成功 (合計時間: 0 秒)
```
- shutdown() なし
```
run:
MAIN:main
SUB :pool-1-thread-1
構築成功 (合計時間: 30 秒)
```
  プールしているスレッドがタイムアウトするまでアプリが終わらない

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