多線程復(fù)習(xí)

多線程的基本概念

什么是一個(gè)線程？如何開(kāi)啟一個(gè)線程？

package com.mashibing.juc.c_000;import java.util.concurrent.TimeUnit;public class T01_WhatIsThread {private static class T1 extends Thread {@Overridepublic void run() {for(int i=0; i<10; i++) {try {TimeUnit.MICROSECONDS.sleep(1);} catch (InterruptedException e) {e.printStackTrace();}System.out.println("T1");}}}public static void main(String[] args) {//new T1().run();//這是普通的函數(shù)調(diào)用new T1().start();//這是開(kāi)啟一個(gè)線程for(int i=0; i<10; i++) {try {TimeUnit.MICROSECONDS.sleep(1);} catch (InterruptedException e) {e.printStackTrace();}System.out.println("main");}} }

面試題：請(qǐng)你告訴我啟動(dòng)線程的三種方式

• 繼承Thread，重寫(xiě)run方法
• 實(shí)現(xiàn)Runnable接口，重寫(xiě)run方法（或Lambda表達(dá)式）
• 通過(guò)線程池來(lái)啟動(dòng)（實(shí)際上也是以上兩種之一）

package com.mashibing.juc.c_000;public class T02_HowToCreateThread {static class MyThread extends Thread {@Overridepublic void run() {System.out.println("Hello MyThread!");}}static class MyRun implements Runnable {@Overridepublic void run() {System.out.println("Hello MyRun!");}}public static void main(String[] args) {new MyThread().start(); // 第一種new Thread(new MyRun()).start(); // 第二種（1）new Thread(()->{ // 第二種（2）System.out.println("Hello Lambda!");}).start();} } //請(qǐng)你告訴我啟動(dòng)線程的三種方式 1：Thread 2: Runnable 3:Executors.newCachedThrad

Sleep Yield Join 的含義

• sleep：睡眠，當(dāng)前線程暫停一段時(shí)間，讓給別的線程去執(zhí)行。睡眠時(shí)間到，自動(dòng)復(fù)活
• yield：當(dāng)前線程正在執(zhí)行的時(shí)候，停下來(lái)進(jìn)入等待隊(duì)列，回到等待隊(duì)列里。系統(tǒng)調(diào)度算法去決定哪個(gè)線程繼續(xù)運(yùn)行（有可能還是自己）
• join：在自己當(dāng)前線程加入你調(diào)用的join線程，本線程等待等調(diào)用的線程運(yùn)行完了，自己再去執(zhí)行。（自己join自己沒(méi)有意義）

package com.mashibing.juc.c_000;public class T03_Sleep_Yield_Join {public static void main(String[] args) { // testSleep(); // testYield();testJoin();}static void testSleep() {new Thread(()->{for(int i=0; i<100; i++) {System.out.println("A" + i);try {Thread.sleep(500);//TimeUnit.Milliseconds.sleep(500)} catch (InterruptedException e) {e.printStackTrace();}}}).start();}static void testYield() {new Thread(()->{for(int i=0; i<100; i++) {System.out.println("A" + i);if(i%10 == 0) Thread.yield();}}).start();new Thread(()->{for(int i=0; i<100; i++) {System.out.println("------------B" + i);if(i%10 == 0) Thread.yield();}}).start();}static void testJoin() {Thread t1 = new Thread(()->{for(int i=0; i<100; i++) {System.out.println("A" + i);try {Thread.sleep(500);//TimeUnit.Milliseconds.sleep(500)} catch (InterruptedException e) {e.printStackTrace();}}});Thread t2 = new Thread(()->{try {t1.join();} catch (InterruptedException e) {e.printStackTrace();}for(int i=0; i<100; i++) {System.out.println("A" + i);try {Thread.sleep(500);//TimeUnit.Milliseconds.sleep(500)} catch (InterruptedException e) {e.printStackTrace();}}});t1.start();t2.start();} }

線程狀態(tài)

如何關(guān)閉線程？
不要使用stop()關(guān)閉線程，要讓線程自己去結(jié)束。

package com.mashibing.juc.c_000;public class T04_ThreadState {static class MyThread extends Thread {@Overridepublic void run() {System.out.println(this.getState());for(int i=0; i<10; i++) {try {Thread.sleep(500);} catch (InterruptedException e) {e.printStackTrace();}System.out.println(i);}}}public static void main(String[] args) {Thread t = new MyThread();System.out.println(t.getState());t.start();try {t.join();} catch (InterruptedException e) {e.printStackTrace();}System.out.println(t.getState());} }

Interrupt 的含義

當(dāng) catch 到 InterruptedException 時(shí)，應(yīng)該在邏輯中寫(xiě)好處理方式：讓線程停止或者繼續(xù)運(yùn)行

Syncronized 復(fù)習(xí)

給一個(gè)變量/一段代碼加鎖的含義是：線程拿到鎖之后，才能修改一個(gè)變量/執(zhí)行一段代碼

/*** synchronized關(guān)鍵字* 對(duì)某個(gè)對(duì)象加鎖*/package com.mashibing.juc.c_001;public class T {private int count = 10;private Object o = new Object();public void m() {synchronized(o) { //任何線程要執(zhí)行下面的代碼，必須先拿到o的鎖count--;System.out.println(Thread.currentThread().getName() + " count = " + count);}} } /*** synchronized關(guān)鍵字* 對(duì)某個(gè)對(duì)象加鎖* @author mashibing*/package com.mashibing.juc.c_002;public class T {private int count = 10;public void m() {synchronized(this) { //任何線程要執(zhí)行下面的代碼，必須先拿到this的鎖count--;System.out.println(Thread.currentThread().getName() + " count = " + count);}} } /*** synchronized關(guān)鍵字* 對(duì)某個(gè)對(duì)象加鎖* @author mashibing*/package com.mashibing.juc.c_003;public class T {private int count = 10;public synchronized void m() { //等同于在方法的代碼執(zhí)行時(shí)要synchronized(this)count--;System.out.println(Thread.currentThread().getName() + " count = " + count);} } /*** synchronized關(guān)鍵字* 對(duì)某個(gè)對(duì)象加鎖* @author mashibing*/package com.mashibing.juc.c_004;public class T {private static int count = 10;public synchronized static void m() { //這里等同于synchronized(FineCoarseLock.class)count--;System.out.println(Thread.currentThread().getName() + " count = " + count);}public static void mm() {synchronized(T.class) { //考慮一下這里寫(xiě)synchronized(this)是否可以？count --;}} }

測(cè)試將syncronized方法和非syncronized方法一起調(diào)用：非syncronized方法并沒(méi)有被阻塞

/*** 同步和非同步方法是否可以同時(shí)調(diào)用？* @author mashibing*/package com.mashibing.juc.c_007;public class T {public synchronized void m1() { System.out.println(Thread.currentThread().getName() + " m1 start...");try {Thread.sleep(10000);} catch (InterruptedException e) {e.printStackTrace();}System.out.println(Thread.currentThread().getName() + " m1 end");}public void m2() {try {Thread.sleep(5000);} catch (InterruptedException e) {e.printStackTrace();}System.out.println(Thread.currentThread().getName() + " m2 ");}public static void main(String[] args) {T t = new T();/*new Thread(()->t.m1(), "t1").start();new Thread(()->t.m2(), "t2").start();*/new Thread(t::m1, "t1").start();new Thread(t::m2, "t2").start();/*//1.8之前的寫(xiě)法new Thread(new Runnable() {@Overridepublic void run() {t.m1();}});*/ } }

示例：臟讀

/*** 面試題：模擬銀行賬戶* 對(duì)業(yè)務(wù)寫(xiě)方法加鎖* 對(duì)業(yè)務(wù)讀方法不加鎖* 這樣行不行？** 容易產(chǎn)生臟讀問(wèn)題（dirtyRead）*/package com.mashibing.juc.c_008;import java.util.concurrent.TimeUnit;public class Account {String name;double balance;public synchronized void set(String name, double balance) {this.name = name;try {Thread.sleep(2000);} catch (InterruptedException e) {e.printStackTrace();}this.balance = balance;}public /*synchronized*/ double getBalance(String name) {return this.balance;}public static void main(String[] args) {Account a = new Account();new Thread(()->a.set("zhangsan", 100.0)).start();try {TimeUnit.SECONDS.sleep(1);} catch (InterruptedException e) {e.printStackTrace();}System.out.println(a.getBalance("zhangsan"));try {TimeUnit.SECONDS.sleep(2);} catch (InterruptedException e) {e.printStackTrace();}System.out.println(a.getBalance("zhangsan"));} }

總結(jié)

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