java多线程（一）

一、invokeAll

　　Executors支持通过invokeAll()一次批量提交多个callable。这个方法结果一个callable的集合，然后返回一个future的列表。

public static void main(String[] args) throws InterruptedException {
        // 根据cpu是几核来开启几个线程
        ExecutorService service = Executors.newWorkStealingPool();
        List<Callable<String>> callables = Arrays.asList(
                () -> "task1",
                () -> "task2",
                () -> "task3",
                () -> "task4",
                () -> "task5");

        service.invokeAll(callables)
                .stream()
                .map(future -> {
                    try {
                        return future.get();
                    }
                    catch (Exception e) {
                        throw new IllegalStateException(e);
                    }
                })
                .forEach(System.out::println);
    }

　　看一下Executors.newWorkStealingPool()调用源码为：

/**
     * Creates a work-stealing thread pool using all
     * {@link Runtime#availableProcessors available processors}
     * as its target parallelism level.
     * @return the newly created thread pool
     * @see #newWorkStealingPool(int)
     * @since 1.8
     */
    public static ExecutorService newWorkStealingPool() {
        return new ForkJoinPool
            (Runtime.getRuntime().availableProcessors(),
             ForkJoinPool.defaultForkJoinWorkerThreadFactory,
             null, true);
    }

　　实际上Runtime.getRuntime().availableProcessors()获取CPU是集合，那么就开启几个线程来执行（通常默认为JVM可用的处理器个数）。

　　

　　看到还有另外一个ForkJoinPool.defaultForkJoinWorkerThreadFactory，源码是这样的：

/**
  * Default ForkJoinWorkerThreadFactory implementation; creates a
  * new ForkJoinWorkerThread.
  */
  static final class DefaultForkJoinWorkerThreadFactory
        implements ForkJoinWorkerThreadFactory {
        public final ForkJoinWorkerThread newThread(ForkJoinPool pool) {
            return new ForkJoinWorkerThread(pool);
        }
    }

　　结合其他源码看起来ForkJoinPool：

　　1.初始化了一个线程池ForkJoinWorkerThread[parallelism..

　　2.初始化了一个任务队列submissionQueue[8]。

　--->每天进步一点！！！<---