Fork/Join——ForkJoinPool核心方法（二）

╰+攻爆jí腚メ 2021-08-30 20:15 459阅读 0赞

#### 12. ####

方法
    public boolean isShutdown()
    的使用

public class Demo3 { 
        public static void main(String[] args) throws InterruptedException { 
            Runnable runnable = new Runnable() { 
                @Override
                public void run() { 
                    try { 
                        System.out.println("打印了！begin " + Thread.currentThread().getName());
                        Thread.sleep(1000);
                        System.out.println("打印了！end" + Thread.currentThread().getName());
                    } catch (InterruptedException e) { 
                        e.printStackTrace();
                    }
                }
            };
    
            ForkJoinPool pool = new ForkJoinPool();
            pool.execute(runnable);
            System.out.println("A=" + pool.isShutdown());
            pool.shutdown();
            Thread.sleep(5000);
            System.out.println("B=" + pool.isShutdown());
        }
    }

任务成功被运行。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NvbGRfX19wbGF5_size_16_color_FFFFFF_t_70]

public class Demo3 { 
        public static void main(String[] args) throws InterruptedException { 
            Runnable runnable = new Runnable() { 
                @Override
                public void run() { 
                    try { 
                        System.out.println("打印了！begin " + Thread.currentThread().getName());
                        Thread.sleep(1000);
                        System.out.println("打印了！end" + Thread.currentThread().getName());
                    } catch (InterruptedException e) { 
                        e.printStackTrace();
                    }
                }
            };
    
            ForkJoinPool pool = new ForkJoinPool();
            pool.execute(runnable);
            System.out.println("A=" + pool.isShutdown());
            pool.shutdownNow();
            Thread.sleep(5000);
            System.out.println("B=" + pool.isShutdown());
        }
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NvbGRfX19wbGF5_size_16_color_FFFFFF_t_70 1]

任务成功被运行，由于shutdownNow()方法在源代码内部使用了interrupt() 方法，所以interrupt()方法遇到sleep()抛出“ java.lang.InterruptedException: sleep interrupted”异常。

如果使用Callable接口，则需要使用Future对象的get()方法获得异常。

#### 13. ####

方法
    public boolean awaitTermination(long timeout, TimeUnit unit)
    的使用

方法awaitTermination(long timeout, TimeUnit unit)的作用是等待池被销毁的最长时间，具有阻塞特性。

public class Demo4 { 
        public static void main(String[] args) throws InterruptedException { 
            Runnable_a a = new Runnable_a();
            ForkJoinPool pool = new ForkJoinPool();
            pool.execute(a);
            System.out.println("main begin! " + System.currentTimeMillis());
            //awaitTermination具有阻塞特性
            System.out.println(pool.awaitTermination(10, TimeUnit.SECONDS));
            System.out.println("main end! " + System.currentTimeMillis());
        }
    }
    
    class Runnable_a implements  Runnable { 
    
        @Override
        public void run() { 
            try { 
                System.out.println("begin " + Thread.currentThread().getName() + " " + System.currentTimeMillis());
                Thread.sleep(4000);
                System.out.println("end " + Thread.currentThread().getName() + " " + System.currentTimeMillis());
            } catch (InterruptedException e) { 
                e.printStackTrace();
            }
        }
    }
    
    class Runnable_b implements  Runnable { 
    
        @Override
        public void run() { 
            try { 
                Thread.sleep(5000);
            } catch (InterruptedException e) { 
                e.printStackTrace();
            }
        }
    }

返回值打印false，说明任务池并没有被销毁。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NvbGRfX19wbGF5_size_16_color_FFFFFF_t_70 2]

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NvbGRfX19wbGF5_size_16_color_FFFFFF_t_70 3]  
日志main begin和main end之间的时差差4秒，返回值打印true,代表任务池在4秒后.被销毁，所以awaitTermination(long timeout, TimeUnit unit)要结合shutdown()方法进行使用。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NvbGRfX19wbGF5_size_16_color_FFFFFF_t_70 4]

#### 14. ####

方法
    public <T> T invoke(ForkJoinTask<T> task)
    的使用

public class Demo5 { 
        public static void main(String[] args) { 
            RecursiveAction_ action = new RecursiveAction_();
            ForkJoinPool pool = new ForkJoinPool();
            pool.invoke(action);
        }
    }
    
    
    class RecursiveAction_ extends RecursiveAction { 
    
        @Override
        protected void compute() { 
            System.out.println("TheadName=" + Thread.currentThread().getName());
        }
    }
    
    class RecursiveTask_ extends RecursiveTask<String> { 
    
        @Override
        protected String compute() { 
            return "我是返回值";
        }
    }

![在这里插入图片描述][202006251831308.png]

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NvbGRfX19wbGF5_size_16_color_FFFFFF_t_70 5]  
![在这里插入图片描述][20200625183405746.png]

方法execute(task)、submit(task) 以及invoke(task) 都可以在异步队列中执行任务，需要注意的是，`方法invoke()是阻塞的`，而它们在使用上的区别其实很简单:

*  execute(task) 只执行任务，没有返回值
 *  而submit(task)方法有返回值，返回值类型是ForkJoinTask， 想取得返回值时，需要使用ForkJoinTask对象的get() 方法
 *  而invoke(task)和submit(task)方法一样都具有返回值的功能，区别就是invoke(task)方法直接将返回值进行返回，而不是通过ForkJoinTask对象的get(方法。

这3个方法的声明如下:

pool.execute(task);
    //pulic void execute(ForkJoinTask<?> task)
    
    pool.submit(task);
    //public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task)
    
    pool.invoke(task);
    //public <T> T invoke(ForkJoinTask<T> task)

#### 15. 监视pool池的状态 ####

*  方法`getParallelism()`:获得并行的数量，与CPU的内核数有关;
 *  方法`getPoolSize()`:获得任务池的大小;
 *  方法`getQueuedSubmissionCount()`:取得已经提交但尚未被执行的任务数量;
 *  方法`hasQueuedSubmissions()`:判断队列中是否有未执行的任务;
 *  方法`getActiveThreadCount()`:获得活动的线程个数;
 *  方法`getQueuedTaskCount()`:获得任务的总个数;
 *  方法`getStealCount()`:获得偷窃的任务个数;
 *  方法`getRunningThreadCount()`:获得正在运行并且不在阻塞状态下的线程个数;
 *  方法`isQuiescent()`:判断任务池是否是静止未执行任务的状态。

public class Demo6 { 
        public static void main(String[] args) { 
            MyRecursiveTask_1 task_1 = new MyRecursiveTask_1();
            MyRecursiveTask_1 task_2 = new MyRecursiveTask_1();
            MyRecursiveTask_1 task_3 = new MyRecursiveTask_1();
            ForkJoinPool pool = new ForkJoinPool();
            pool.submit(task_1);
            pool.submit(task_2);
            pool.submit(task_3);
            System.out.println("并行数getParallelism()=" + pool.getParallelism());
            System.out.println("线程池大小getPoolSize()=" + pool.getPoolSize());
            do { 
            }while (!pool.isTerminated());
            System.out.println("main end");
        }
    }
    
    class MyRecursiveTask_1 extends RecursiveAction { 
    
        @Override
        protected void compute() { 
            try { 
                System.out.println("begin=" + Thread.currentThread().getName());
                Thread.sleep(1000);
                System.out.println("end=" + Thread.currentThread().getName());
            } catch (InterruptedException e) { 
                e.printStackTrace();
            }
        }
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NvbGRfX19wbGF5_size_16_color_FFFFFF_t_70 6]

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NvbGRfX19wbGF5_size_16_color_FFFFFF_t_70 7]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NvbGRfX19wbGF5_size_16_color_FFFFFF_t_70 8]

#### ForkJoinTask对异常的处理 ####

*  方法`isCompletedAbnormally()`判断任务是否出现异常
 *  方法`isCompletedNormally()`判断任务是否正常执行完毕
 *  方法`getException()`返回报错异常

public class Demo7 { 
        public static void main(String[] args) throws InterruptedException { 
            MyRecursiveTaskX taskX = new MyRecursiveTaskX();
            ForkJoinPool pool = new ForkJoinPool();
            ForkJoinTask<Integer> submit = pool.submit(taskX);
            System.out.println(submit.isCompletedAbnormally() + " " + submit.isCompletedNormally());
            Thread.sleep(2000);
            System.out.println(submit.isCompletedAbnormally() + " " + submit.isCompletedNormally());
            System.out.println(submit.getException());
        }
    }
    
    class MyRecursiveTaskX extends RecursiveTask<Integer> { 
    
        @Override
        protected Integer compute() { 
            try { 
                Thread.sleep(1000);
                Integer.parseInt("a");
            } catch (NumberFormatException e) { 
                e.printStackTrace();
                //需要抛出NumberFromatException异常，MyRecursiveTaskX对象从而可以获得任务执行的结果的情况
                throw e;
            } catch (InterruptedException e) { 
                e.printStackTrace();
            }
            return 100;
        }
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NvbGRfX19wbGF5_size_16_color_FFFFFF_t_70 9]

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[202006251831308.png]: /images/20210813/c20d15fd032c42ffaf08e4bb552d0fce.png
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