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一、进程与线程
1.进程和线程的由来
(1)串行:初级计算机只能串行执行任务,并且需要长时间等待用户输入
(2)批处理:预先将用户的指令集中成清单,批量串行处理用户指令,仍然无法并发执行 (3)进程:进程独占内存空间,保存各自运行状态,相互之间不干扰且可以互相切换,并为并发处理任务提供了可能 (4)线程:共享进程的内存资源,相互间切换更快捷,支持更细粒度的任务控制,使进程内的子任务得以并发执行。2.进程和线程区别
总括:进程是资源分配的最小单位,线程是cpu调度的最小单位
| 进程 | 线程 |
独立应用 | 能 | 不能 |
独立的地址空间 | 有,相互不影响 | 无,只是进程的不同路径 |
独立的地址空间 | 有 | 无 |
切换开销 | 大 | 小 |
3.关系
(1)JAVA对操作系统提供的功能进行封装,包括进程和线程
(2)运行一个程序会产生一个进程,进程包含至少一个线程(主线程) (3)每个进程对应一个JVM实例,多个线程共享JVM里的堆 (4)Java采用单线程变成模型,程序自动创建主线程 (5)主线程可以创建子线程,原则上主线程要后于子线程完成执行。二、Runnable、Thread、Callable和线程池实现多线程
1.通过runnable接口实现多线程
package thread;public class mythread { public static void main(String[] args) { System.out.println("cuuurent thread:"+ Thread.currentThread().getName()); //测试实现接口线程:java.thread.mythreadofRunnable //1.实现接口 Runnable threadrun=new mythreadofRunnable(); //2.通过接口实现Thread Thread t1=new Thread(threadrun); //3.通过(Thread)t1对象start运行方法 t1.start(); for (int i=0;i<10;i++){ System.out.println("线程外部方法第"+i+"次输出"); } }}/** * 线程1 * 实现接口线程:java.thread.mythreadofRunnable * 实现方法:重写run方法 */class mythreadofRunnable implements Runnable{ public void run(){ int count=0; while (count<=10){ if (count%2==0){ System.out.println("count="+count); } count++; } System.out.println("cuuurent thread:"+ Thread.currentThread().getName()); }}
2.通过thread类实现多线程
package thread;public class mythread { public static void main(String[] args) { System.out.println("cuuurent thread:"+ Thread.currentThread().getName()); //测试实现接口线程:java.thread.mythreadofRunnable //1.实现接口 Runnable threadrun=new mythreadofRunnable(); //2.通过接口实现Thread Thread t1=new Thread(threadrun); //3.通过(Thread)t1对象start运行方法 t1.start(); for (int i=0;i<10;i++){ System.out.println("线程外部方法第"+i+"次输出"); } //测试集成thread类线程:java.thread.mythreadofThread //1.实现mythreadofThread线程类 mythreadofThread t2=new mythreadofThread(); //2.通过(Thread)t2对象start运行方法 t2.start(); for (int i=0;i<10;i++){ System.out.println("线程外部方法第"+i+"次输出"); } }}/** * 线程1 * 实现接口线程:java.thread.mythreadofRunnable * 实现方法:重写run方法 */class mythreadofRunnable implements Runnable{ public void run(){ int count=0; while (count<=10){ if (count%2==0){ System.out.println("count="+count); } count++; } System.out.println("cuuurent thread:"+ Thread.currentThread().getName()); }}/** * 线程2 * 继承Thread类:java.thread.mythreadofThread * 实现方法:重写run方法 */class mythreadofThread extends Thread{ int count=0; public void run(){ while (count<=10){ if (count%2==0){ System.out.println("count="+count); } count++; } System.out.println("cuuurent thread:"+ Thread.currentThread().getName()); }}
3.通过继承Collable类实现有返回值的多线程
package thread;import java.util.concurrent.Callable;public class mycallableNew implements Callable{ int sum=0; public Integer call() throws Exception {// return null; String value="callable test"; System.out.println("Ready to work"); Thread.currentThread().sleep(3000); for (int i=0;i<10;i++){ sum+=i; } System.out.println("task done"); return sum; }}
测试代码
package thread;import java.util.concurrent.ExecutionException;import java.util.concurrent.Future;import java.util.concurrent.FutureTask;public class SyncDemo2 { public static void main(String... args) { mycallableNew mycallablenew=new mycallableNew(); FutureTask futureTask=new FutureTask(mycallablenew); new Thread(futureTask).start(); try { System.out.println(futureTask.get()); } catch (InterruptedException e) { e.printStackTrace(); } catch (ExecutionException e) { e.printStackTrace(); } }}
结果:
Ready to work
task done 454.通过Executors.newFixedThreadPool线程池实现多线程提交
(1)execute:提交不要求有返回值的任务
(2)submit:提交有返回结果的任务,运行完返回结果
package thread;import java.util.ArrayList;import java.util.concurrent.*;public class threadpoolimp { public static void main(String[] args) { ExecutorService executorService= Executors.newFixedThreadPool(5); //execute执行过程 //execute:不要求有返回值;submit提交有返回任务 executorService.execute(new Thread()); executorService.execute(new Runnable() { @Override public void run() { System.out.println("implentment runnable!"); } }); //submit提交有返回结果的任务,运行完返回结果 Future future=executorService.submit(new Callable(){ @Override public String call() throws Exception { return "Callable thread;";// return null; } }); try { System.out.println(future.get()); } catch (InterruptedException e) { e.printStackTrace(); } catch (ExecutionException e) { e.printStackTrace(); } //将有返回值的线程的值,存进集合 ArrayList list=new ArrayList<>(); for (int i = 0; i < 5; i++) { int finals=i; Future future1=executorService.submit(new Callable () { @Override public String call() throws Exception { return "return is :"+finals; } }); try { list.add((String)future1.get()); } catch (InterruptedException e) { e.printStackTrace(); } catch (ExecutionException e) { e.printStackTrace(); } } for (String s : list) { System.out.println(s); } }}
结果:
implentment runnable!Callable thread;return is :0return is :1return is :2return is :3return is :4
三、实现主线程等待子线程结束
1.目的
有的主线程程序,需要子线程运行结束的结果,从而实现精确控制。
2.方法一:主线程等待法
(1)原理:主线程通过监控子线程对应对象值,当子线程对象值被获取时,认为子线程执行完成;否则,主线程一直等待
(2)实现代码:package thread;public class cyclewait implements Runnable { private String value; /** * 等待7秒后再给value赋值 */ public void run() { try { Thread.currentThread().sleep(7000); } catch (InterruptedException e) { e.printStackTrace(); } value="we have done now"; } public static void main(String[] args) throws InterruptedException { //1.创建子线程 cyclewait mcw=new cyclewait(); Thread t=new Thread(mcw); //2.开启子线程 t.start(); //3.主线程等待 while (mcw.value==null){ Thread.currentThread().sleep(1000); } System.out.println("value : " +mcw.value); }}
3.方法二:join方法
(1)原理:使用Thread类的join阻塞当前线程以等待子线程处理完毕
(2)代码package thread;public class cyclewait implements Runnable { private String value; /** * 等待7秒后再给value赋值 */ public void run() { try { Thread.currentThread().sleep(7000); } catch (InterruptedException e) { e.printStackTrace(); } value="we have done now"; } public static void main(String[] args) throws InterruptedException { //1.创建子线程 cyclewait mcw=new cyclewait(); Thread t=new Thread(mcw); //2.开启子线程 t.start(); //3.1主线程等待// while (mcw.value==null){// Thread.currentThread().sleep(1000);// }// System.out.println("value : " +mcw.value); //3.2 join方法:主线程阻塞 t.join(); System.out.println("value : " +mcw.value); }}
4.方法三:通过callable接口实现,通过FutureTask
(1)Callable类
package thread;import java.util.concurrent.Callable;public class mycallable implements Callable{ public String call() throws Exception {// return null; String value="callable test"; System.out.println("Ready to work"); Thread.currentThread().sleep(3000); System.out.println("task done"); return value; }}
(2)通过futuretask实现
package thread;import java.util.concurrent.ExecutionException;import java.util.concurrent.FutureTask;public class mycallablefuturetaskimp { public static void main(String[] args) throws ExecutionException, InterruptedException { FutureTasktask=new FutureTask (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()); }}
(3)通过线程池实现:通过线程池获取返回值
package thread;import java.util.concurrent.ExecutionException;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import java.util.concurrent.Future;public class mycallable_threadpoolimp { public static void main(String[] args) { ExecutorService newCachedThreadPool= Executors.newCachedThreadPool(); Futurefuture=newCachedThreadPool.submit(new mycallable()); //1.判断是否执行完,没有执行完,给出提示 if(!future.isDone()){ System.out.println("task has not finished, please wait"); } //2.阻塞主线程,直到子线程执行结束 try { System.out.println(future.get()); } catch (InterruptedException e) { e.printStackTrace(); } catch (ExecutionException e) { e.printStackTrace(); }finally { newCachedThreadPool.shutdown(); } }}
四、线程的状态
1.新建状态(New):创建后尚未启动的线程
2.运行(Runnable):
(1)Running:获得cpu资源,正在运行 (2)Ready:还没有获得cpu资源3.阻塞
(1)无限期等待(Waiting):不会被分配CPU执行时间,需要显示被唤醒 (2)限期等待(Timed Waiting):在一定时间后会由系统自动唤醒 (3)阻塞(Blocked):等待获取排它锁4.结束(Terminated):已终止线程的状态,线程已经结束执行。终止状态的线程不能重新启动。
五、线程调度
1.wait
作用:等待一定时间,让出cpu资源,并且释放同步锁lock。执行A,然后A通过wait释放同步锁,然后执行B,最后,等B执行完成后执行A。
package thread;public class waitandsleep { public static void main(String[] args) { final Object lock=new Object(); //线程A:执行wait逻辑 new Thread(new Runnable() { public void run() { System.out.println("Thread A is waiting to get the lock."); synchronized (lock){ try { System.out.println("thread A get lock"); Thread.sleep(20); System.out.println("thread A do wait method"); lock.wait(1000);// Thread.sleep(1000); System.out.println("thread A is done"); } catch (InterruptedException e) { e.printStackTrace(); } } } }).start(); //保证线程A先执行 try { Thread.sleep(10); } catch (InterruptedException e) { e.printStackTrace(); } //线程B:执行sleep逻辑 new Thread(new Runnable() { public void run() { System.out.println("Thread B is waiting to get the lock."); synchronized (lock){ try { System.out.println("thread B get lock"); System.out.println("thread B is sleeping 10 ms"); Thread.sleep(10);// lock.wait(10); System.out.println("thread B is done"); } catch (InterruptedException e) { e.printStackTrace(); } } } }).start(); }}执行结果:thread.waitandsleepThread A is waiting to get the lock.thread A get lockThread B is waiting to get the lock.thread A do wait methodthread B get lockthread B is sleeping 10 msthread B is donethread A is doneProcess finished with exit code 0
2.Sleep
作用:等待一定时间,但是不释放同步锁。执行过程时,A执行完成,再执行B
package thread;public class waitandsleep { public static void main(String[] args) { final Object lock=new Object(); //线程A:执行wait逻辑 new Thread(new Runnable() { public void run() { System.out.println("Thread A is waiting to get the lock."); synchronized (lock){ try { System.out.println("thread A get lock"); Thread.sleep(20); System.out.println("thread A do wait method");// lock.wait(1000); Thread.sleep(1000); System.out.println("thread A is done"); } catch (InterruptedException e) { e.printStackTrace(); } } } }).start(); //保证线程A先执行 try { Thread.sleep(10); } catch (InterruptedException e) { e.printStackTrace(); } //线程B:执行sleep逻辑 new Thread(new Runnable() { public void run() { System.out.println("Thread B is waiting to get the lock."); synchronized (lock){ try { System.out.println("thread B get lock"); System.out.println("thread B is sleeping 10 ms");// Thread.sleep(10); lock.wait(10); System.out.println("thread B is done"); } catch (InterruptedException e) { e.printStackTrace(); } } } }).start(); }}结果:thread.waitandsleepThread A is waiting to get the lock.thread A get lockThread B is waiting to get the lock.thread A do wait methodthread A is donethread B get lockthread B is sleeping 10 msthread B is doneProcess finished with exit code 0
3.通知notify或notifyall
(1)二者区别
notify:随机选取一个处于等待池中的线程进入锁池去竞争获取锁的机会
notifyAll:会让所有处于等待池的线程全部进入锁池去竞争获取锁的机会
(2)代码
package thread;public class waitandsleep_notify { public static void main(String[] args) { final Object lock=new Object(); //线程A:执行wait逻辑 new Thread(new Runnable() { public void run() { System.out.println("Thread A is waiting to get the lock."); synchronized (lock){ try { System.out.println("thread A get lock"); Thread.sleep(20); System.out.println("thread A do wait method"); //无限期等待,需要额外线程唤醒 lock.wait();// Thread.sleep(1000); System.out.println("thread A is done"); } catch (InterruptedException e) { e.printStackTrace(); } } } }).start(); //保证线程A先执行 try { Thread.sleep(10); } catch (InterruptedException e) { e.printStackTrace(); } //线程B:执行sleep逻辑 new Thread(new Runnable() { public void run() { System.out.println("Thread B is waiting to get the lock."); synchronized (lock){ try { System.out.println("thread B get lock"); System.out.println("thread B is sleeping 10 ms"); Thread.sleep(10);// lock.wait(10); lock.notify(); //或者lock.notifyAll(); System.out.println("thread B is done"); } catch (InterruptedException e) { e.printStackTrace(); } } } }).start(); }}
结果解释,线程B使用lock.notify(),通知正在阻塞的一个线程(当前线程A)进行继续执行
Thread A is waiting to get the lock.thread A get lockThread B is waiting to get the lock.thread A do wait methodthread B get lockthread B is sleeping 10 msthread B is donethread A is done
即如果线程B没有lock.notify(),则线程A不会持续进行,结果是
Thread A is waiting to get the lock.thread A get lockThread B is waiting to get the lock.thread A do wait methodthread B get lockthread B is sleeping 10 msthread B is done
4.yield:线程让步
(1)定义:当调用Thread.yield()函数时,当前线程可能会让出其占用的cpu资源,也可能不会让出其占用的cpu资源。同时,yield也不会释放锁lock,对锁的行为不会有影响。
(2)测试实例
package thread;public class yield { public static void main(String[] args) { Runnable yieldTask=new Runnable() { public void run() { for (int i=1;i<=20;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(); }}
结果:A线程当执行到i=5时,不一定会出让cpu资源。
A1A2A3A4A5B1B2A6B3B4A7B5A8A9A10A11A12B6A13B7A14B8B9A15B10A16A17A18A19A20B11B12B13B14B15B16B17B18B19B20
5.interrupt():中断线程
调用interrupt(),通知线程应该中断
(1)如果线程处于被阻塞状态,那么线程将立即退出被阻塞状态,并且抛出一个InterruptedException异常。 (2)如果线程处于正常活动状态,那么会将该线程的中断标志设置为true。被设置终端标志的线程将继续正常运行,不受影响。转载地址:https://blog.csdn.net/u010886217/article/details/99696822 如侵犯您的版权,请留言回复原文章的地址,我们会给您删除此文章,给您带来不便请您谅解!