多线程和并发

start方法会调用native 修饰的start0方法，这个方法用c实现，这个c又调用了jvm.cpp中的实现的new JavaThread(), 创建了 子线程~~~~

第一种 自己写一个sleep的循环等待 垃圾的一批

第二种 使用 thread.join() 方法等待，，，业务复杂不能并行运行

futureTask 完美解决以上问题， 使用线程池 更方便

callable类

package com.interview.javabasic.thread;

import java.util.concurrent.Callable;

public class MyCallable implements Callable<String> {
    @Override
    public String call() throws Exception{
        String value="test";
        System.out.println("Ready to work");
        Thread.currentThread().sleep(5000);
        System.out.println("task done");
        return  value;
    }

}

callable类使用方式

package com.interview.javabasic.thread;

import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;

public class FutureTaskDemo {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        FutureTask<String> task = new FutureTask<String>(new MyCallable());
        new Thread(task).start();
        if(!task.isDone()){
            System.out.println("task has not finished, please wait!");
        }
        System.out.println("task return: " + task.get());

    }
}

callable类的 线程池使用

package com.interview.javabasic.thread;

import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class ThreadPoolDemo {
    public static void main(String[] args) {
        ExecutorService newCachedThreadPool = Executors.newCachedThreadPool();
        Future<String> future = newCachedThreadPool.submit(new MyCallable());
        if(!future.isDone()){
            System.out.println("task has not finished, please wait!");
        }
        try {
            System.out.println(future.get());
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        } finally {
            newCachedThreadPool.shutdown();//一定记得关闭线程池
        }
    }
}

源码分析

细节 thread 源码中有 所有状态的枚举

run完了继续调用start 抛异常

package com.interview.javabasic.thread;

public class YieldDemo {
    public static void main(String[] args) {
        Runnable yieldTask = new Runnable() {
            @Override
            public void run() {
                for (int i = 1; i <= 10; i++) {
                    System.out.println(Thread.currentThread().getName() + i);
                    if (i == 5) {
                        Thread.yield();
                    }
                }
            }
        };
        Thread t1 = new Thread(yieldTask, "A");
        Thread t2 = new Thread(yieldTask, "B");
        t1.start();
        t2.start();
    }

}