JUC并发编程基础篇第二章之CompletableFuture[加强版的线程]
文章目录
1、 创建线程的几种方式
new thread:
//构造方法给指定的线程指定名称,推荐Thread thread = new Thread(t1) {@Overridepublic void run() {//要执行的任务}};//启动线程thread.start();
new runnable:
Runnable runnable = new Runnable() {@Overridepublic void run() {//要执行的任务}};Thread thread = new Thread(runnable);thread.start();
Future
FutureTask<Integer> task = new FutureTask<>(() -> {System.out.println(执行的任务);return 100;});new Thread(task,t1).start();Integer integer = task.get();System.out.println(结果是+integer);
2、 线程之间的通讯方式
2.1、什么是多线程之前的通讯
其实就是多个线程之间在操作同一个资源,但是操作的动作不同
就比如下图,一个线程进行set方法给属性赋值,另一个线程get方法获取属性的值
而本章中要学习的就是:如何保证线程每写一个值,读线程便同步获取写入的那个值;
2.2、线程讯通之间的问题演示
package com.disney;class Res {public String name;public String sex;public String getName() {return name;}public void setName(String name) {this.name = name;}public String getSex() {return sex;}public void setSex(String sex) {this.sex = sex;}
}/*** 写入的线程** 当为偶数为男孩,奇数为女孩*/
class InputThread extends Thread {private Res res;public InputThread(Res res ) {this.res=res;}@Overridepublic void run() {int count = 0;while (true){if (count==0){res.name="william";res.sex="boy";} else{res.name="tom";res.sex="girl";}//得到count+1的模count=(count+1)%2;}}
}/*** 读取的线程*/
class OutPutThread extends Thread{private Res res;public OutPutThread(Res res ) {this.res=res;}@Overridepublic void run() {while (true){System.out.println(res.name+"======"+res.getSex());}}
}public class MainDemo{public static void main(String[] args) {Res res = new Res();OutPutThread outPutThread = new OutPutThread(res);outPutThread.start();InputThread inputThread = new InputThread(res);inputThread.start();}
}
输出结果
根据现实的结果我们可以看出,本来我们是william和boy在一组进行设置 ,但是发现在进行读的时候,数据发生了交叉,以上的数据就是线程通讯不安全的表现,接下来讲解如何解决这个问题
2.3、synchronized 解决讯通问题
package com.disney;class Res {public String name;public String sex;public String getName() {return name;}public void setName(String name) {this.name = name;}public String getSex() {return sex;}public void setSex(String sex) {this.sex = sex;}
}/*** 写入的线程** 当为偶数为男孩,奇数为女孩*/
class InputThread extends Thread {private Res res;public InputThread(Res res ) {this.res=res;}@Overridepublic void run() {int count = 0;while (true){synchronized (res){if (count==0){res.name="william";res.sex="boy";} else{res.name="tom";res.sex="girl";}//得到count+1的模count=(count+1)%2;}}}
}/*** 读取的线程*/
class OutPutThread extends Thread{private Res res;public OutPutThread(Res res ) {this.res=res;}@Overridepublic void run() {while (true){synchronized (res) {System.out.println(res.name + "======" + res.getSex());}}}
}public class MainDemo{public static void main(String[] args) {Res res = new Res();OutPutThread outPutThread = new OutPutThread(res);outPutThread.start();InputThread inputThread = new InputThread(res);inputThread.start();}
}
输出结果
可以看出来的确姓名和性别之间的对应关系有了匹配,但是并不是符合 我们 输出william->toim->william-tom这样逐一变化的规律
2.4、wait()、notify() 解决讯通问题
wait()、notify()、notifyAll()是三个定义在Object类里的方法,可以用来控制线程的状态。
这三个方法最终调用的都是jvm级的native方法。随着jvm运行平台的不同可能有些许差异。
• 如果对象调用了wait方法就会使持有该对象的线程把该对象的控制权交出去,然后处于等待状态。
• 如果对象调用了notify方法就会通知某个正在等待这个对象的控制权的线程可以继续运行。
• 如果对象调用了notifyAll方法就会通知所有等待这个对象控制权的线程继续运行。
package com.disney;class Res {public String name;public String sex;public boolean flag =false;public String getName() {return name;}public void setName(String name) {this.name = name;}public String getSex() {return sex;}public void setSex(String sex) {this.sex = sex;}}/*** 写入的线程** 当为偶数为男孩,奇数为女孩*/
class InputThread extends Thread {private Res res;public InputThread(Res res ) {this.res=res;}@Overridepublic void run() {int count = 0;while (true){synchronized (res){if (res.flag){try {res.wait();} catch (InterruptedException e) {}}if (count==0){res.name="william";res.sex="boy";} else{res.name="tom";res.sex="girl";}count=(count+1)%2;res.flag=true;//得到count+1的模res.notify();}}}
}/*** 读取的线程*/
class OutPutThread extends Thread{private Res res;public OutPutThread(Res res ) {this.res=res;}@Overridepublic void run() {while (true){synchronized (res) {if (!res.flag) {try {res.wait();} catch (InterruptedException e) {e.printStackTrace();}}System.out.println(res.name + "======" + res.getSex());res.flag=false;res.notify();}}}
}public class MainDemo{public static void main(String[] args) {Res res = new Res();OutPutThread outPutThread = new OutPutThread(res);InputThread inputThread = new InputThread(res);outPutThread.start();inputThread.start();}
}
2.5、Lock,Condtion 解决讯通问题
在 jdk1.5 之后,并发包中新增了 Lock 接口(以及相关实现类)用来实现锁功能,Lock 接口提供了与 synchronized 关键字类似的同步功能,但需要在使用时手动获取锁和释放锁。
Local的作用其实就类似synchronized 。但是因为wait是和synchronized 搭配使用,此时我们使用lock就需要一个能代替wait的方法,此时
Condition 的就诞生啦‘’
package com.disney;import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;class Res {public String name;public String sex;public boolean flag =false;Lock lock = new ReentrantLock();Condition condition = lock.newCondition();public String getName() {return name;}public void setName(String name) {this.name = name;}public String getSex() {return sex;}public void setSex(String sex) {this.sex = sex;}}/*** 写入的线程** 当为偶数为男孩,奇数为女孩*/
class InputThread extends Thread {private Res res;public InputThread(Res res ) {this.res=res;}@Overridepublic void run() {int count = 0;while (true){res.lock.lock();if (res.flag){try {res.condition.await();} catch (InterruptedException e) {e.printStackTrace();}}if (count==0){res.name="william";res.sex="boy";} else{res.name="tom";res.sex="girl";}count=(count+1)%2;res.flag=true;//得到count+1的模res.condition.signal();res.lock.unlock();}}}/*** 读取的线程*/
class OutPutThread extends Thread{private Res res;public OutPutThread(Res res ) {this.res=res;}@Overridepublic void run() {while (true){if (!res.flag) {res.lock.lock();try {res.condition.await();} catch (InterruptedException e) {e.printStackTrace();}}System.out.println(res.name + "======" + res.getSex());res.flag=false;res.condition.signal();res.lock.unlock();}}
}public class MainDemo{public static void main(String[] args) {Res res = new Res();OutPutThread outPutThread = new OutPutThread(res);InputThread inputThread = new InputThread(res);outPutThread.start();inputThread.start();}
}
2、 Future的优缺点
优点: Future配合线程池能够显著提高程序的执行效率
public static void main(String[] args) throws ExecutionException, InterruptedException {long startTime = System.currentTimeMillis();ExecutorService executorService = Executors.newFixedThreadPool(3);FutureTask<String> stringFutureTask1 = new FutureTask<>(() -> {TimeUnit.SECONDS.sleep(5);return over;});executorService.submit(stringFutureTask1);FutureTask<String> stringFutureTask2 = new FutureTask<>(() -> {TimeUnit.SECONDS.sleep(3);return over;});executorService.submit(stringFutureTask2);FutureTask<String> stringFutureTask3 = new FutureTask<>(() -> {TimeUnit.SECONDS.sleep(3);return over;});executorService.submit(stringFutureTask3);System.out.println(stringFutureTask1.get());System.out.println(stringFutureTask2.get());System.out.println(stringFutureTask3.get());executorService.shutdown();long endTime = System.currentTimeMillis();System.out.println(耗时了+(endTime-startTime));}
输出结果:
over
over
over
耗时了5084
可以看到如果是串行输出,结果是5s+3s+3s的耗时;
- 缺点1:Get 方法容易导致堵塞
从上面的程序,我必须得到stringFutureTask1
执行完后,主线程才能执行任务, 输出耗时时间,我们的期望是 stringFutureTask1在耗时5s的时间内
,主线程忙其他事情, 并询问下stringFutureTask1
是否执行完毕, 如果执行完毕,则输出耗时时间;
- 缺点2:Get 方法没有最大等待时间
比如我们最多只能等待5s, 但是如果get()方法执行10s的话, 则会影响我们的程序
- 缺点3: isDone 容易导致cpu轮训空转
public static void main(String[] args) throws ExecutionException, InterruptedException {long startTime = System.currentTimeMillis();ExecutorService executorService = Executors.newFixedThreadPool(3);FutureTask<String> stringFutureTask1 = new FutureTask<>(() -> {TimeUnit.SECONDS.sleep(5);return over;});executorService.submit(stringFutureTask1);executorService.shutdown();while (true) {if (stringFutureTask1.isDone()){long endTime = System.currentTimeMillis();System.out.println(耗时了 + (endTime - startTime));}}}
3、CompletableFuture对Future的改进
对于真正的异步处理我们希望可以通过传入回调函数,在Future结束时自动调用该函数;这样我们就不用等待结果了;
3.1、CompletableFuture的基本结构
public class CompletableFuture<T> implements Future<T>, CompletionStage<T>
-
CompletionStage
代表计算过程的一个阶段,一个阶段完成以后可能会触发另一个阶段; -
一个阶段的计算,可以是一个function,consumer或者runnable. 比如stage.thenApply(x->square(x)).thenAccept(x->system.out.print(x)).thenReturn(()->system.out.println())
-
一个阶段的执行可能是被单个阶段的完成触发,也可能是由多个阶段一起触发;
3.2、创建CompletableFuture四种方式
- runAsync 无返回值
返回值 | 具体方法 |
---|---|
static CompletableFuture | runAsync(Runnable runnable) |
static CompletableFuture | runAsync(Runnable runnable, Executor executor) |
代码示例
public static void main(String[] args) throws Exception {ExecutorService executorService = Executors.newFixedThreadPool(3);CompletableFuture<Void> voidCompletableFuture = CompletableFuture.runAsync(() -> {System.out.println(Thread.currentThread().getName());try {TimeUnit.MILLISECONDS.sleep(500);} catch (InterruptedException e) {e.printStackTrace();}},executorService);System.out.println(voidCompletableFuture.get());}
- supplyAsync有返回值
返回值 | 具体方法 |
---|---|
static CompletableFuture | supplyAsync(Supplier supplier) |
static CompletableFuture | supplyAsync(Supplier supplier, Executor executor) |
public static void main(String[] args) throws Exception {ExecutorService executorService = Executors.newFixedThreadPool(3);CompletableFuture<String> stringCompletableFuture = CompletableFuture.supplyAsync(() -> {System.out.println(Thread.currentThread().getName());try {TimeUnit.MILLISECONDS.sleep(500);} catch (InterruptedException e) {e.printStackTrace();}return over;}, executorService);System.out.println(stringCompletableFuture.get());<br></br> System.out.println(stringCompletableFuture.jion());}输出结果
pool-1-thread-1
over
- 指的注意的是,join方法和get方法,都可以获取返回值,而join没有处理异常而已;他不会要求抛出异常
3.3、CompletableFuture的流式调用
public static void main(String[] args) throws Exception {ExecutorService executorService = Executors.newFixedThreadPool(3);CompletableFuture<String> stringCompletableFuture = CompletableFuture.supplyAsync(() -> {System.out.println(Thread.currentThread().getName());try {TimeUnit.MILLISECONDS.sleep(500);} catch (InterruptedException e) {e.printStackTrace();}return over;}, executorService).whenComplete((v, e) -> {System.out.println(hello +v);if (e == null) {System.out.println(没有异常,更新完成);}}).exceptionally(s -> {s.printStackTrace();System.out.println(异常了,主线程先忙其他事情);return null;});System.out.println(主线程工作);}
扩展: 函数值编程接口
3.4、CompletableFuture常见的用法
对计算结果进行合并
public static void main(String[] args) throws Exception {CompletableFuture<Integer> task1 = CompletableFuture.supplyAsync(() -> {return 1;});CompletableFuture<Integer> task2 = CompletableFuture.supplyAsync(() -> {return 10;});CompletableFuture<Integer> integerCompletableFuture = task1.thenCombine(task2, (x, y) -> {return x + y;});System.out.println(integerCompletableFuture.get());}