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#yyds干货盘点# 关键字: synchronized详解

关键字: synchronized详解

Synchronized的使用

在应用Sychronized关键字时需要把握如下注意点:

一把锁只能同时被一个线程获取,没有获得锁的线程只能等待;

每个实例都对应有自己的一把锁(this),不同实例之间互不影响;例外:锁对象是*.class以及synchronized修饰的是static方法的时候,所有对象公用同一把锁

synchronized修饰的方法,无论方法正常执行完毕还是抛出异常,都会释放锁

对象锁

包括方法锁(默认锁对象为this,当前实例对象)和同步代码块锁(自己指定锁对象)

代码块形式:手动指定锁定对象,也可是是this,也可以是自定义的锁

public class SynchronizedObjectLock implements Runnable {
static SynchronizedObjectLock instence = new SynchronizedObjectLock();

@Override
public void run() {
// 同步代码块形式——锁为this,两个线程使用的锁是一样的,线程1必须要等到线程0释放了该锁后,才能执行
synchronized (this) {
System.out.println("我是线程" + Thread.currentThread().getName());
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + "结束");
}
}

public static void main(String[] args) {
Thread t1 = new Thread(instence);
Thread t2 = new Thread(instence);
t1.start();
t2.start();
}
}

public class SynchronizedObjectLock implements Runnable {
static SynchronizedObjectLock instence = new SynchronizedObjectLock();
// 创建2把锁
Object block1 = new Object();
Object block2 = new Object();

@Override
public void run() {
// 这个代码块使用的是第一把锁,当他释放后,后面的代码块由于使用的是第二把锁,因此可以马上执行
synchronized (block1) {
System.out.println("block1锁,我是线程" + Thread.currentThread().getName());
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("block1锁,"+Thread.currentThread().getName() + "结束");
}

synchronized (block2) {
System.out.println("block2锁,我是线程" + Thread.currentThread().getName());
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("block2锁,"+Thread.currentThread().getName() + "结束");
}
}

public static void main(String[] args) {
Thread t1 = new Thread(instence);
Thread t2 = new Thread(instence);
t1.start();
t2.start();
}
}

方法锁形式:synchronized修饰普通方法,锁对象默认为this

public class SynchronizedObjectLock implements Runnable {
static SynchronizedObjectLock instence = new SynchronizedObjectLock();

@Override
public void run() {
method();
}

public synchronized void method() {
System.out.println("我是线程" + Thread.currentThread().getName());
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + "结束");
}

public static void main(String[] args) {
Thread t1 = new Thread(instence);
Thread t2 = new Thread(instence);
t1.start();
t2.start();
}
}

类锁

指synchronize修饰静态的方法或指定锁对象为Class对象

​synchronize修饰静态方法

public class SynchronizedObjectLock implements Runnable {
static SynchronizedObjectLock instence1 = new SynchronizedObjectLock();
static SynchronizedObjectLock instence2 = new SynchronizedObjectLock();

@Override
public void run() {
method();
}

// synchronized用在普通方法上,默认的锁就是this,当前实例
public synchronized void method() {
System.out.println("我是线程" + Thread.currentThread().getName());
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + "结束");
}

public static void main(String[] args) {
// t1和t2对应的this是两个不同的实例,所以代码不会串行
Thread t1 = new Thread(instence1);
Thread t2 = new Thread(instence2);
t1.start();
t2.start();
}
}

synchronized指定锁对象为Class对象

public class SynchronizedObjectLock implements Runnable {
static SynchronizedObjectLock instence1 = new SynchronizedObjectLock();
static SynchronizedObjectLock instence2 = new SynchronizedObjectLock();

@Override
public void run() {
// 所有线程需要的锁都是同一把
synchronized(SynchronizedObjectLock.class){
System.out.println("我是线程" + Thread.currentThread().getName());
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + "结束");
}
}

public static void main(String[] args) {
Thread t1 = new Thread(instence1);
Thread t2 = new Thread(instence2);
t1.start();
t2.start();
}
}
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