Java 同步代码块 - Synchronized Blocks - Java

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java锁实现原理：

http://blog.csdn.net/endlu/article/details/51249156

The synchronized keyword can be used to mark four different types of blocks:

Instance methods
Static methods
Code blocks inside instance methods
Code blocks inside static methods

Instance methods & Code blocks inside instance methods

Java实例方法同步是同步在拥有该方法的对象上

同步构造器中用括号括起来的对象叫做监视器对象

public class SyncBlockTest { public static void main(String[] args) {
ExecutorService es = Executors.newFixedThreadPool(2);
final MySyncBlockClass syncBlockClass = new MySyncBlockClass();
es.submit(new Runnable() {
@Override
public void run() {
try {
syncBlockClass.mehtod1();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
});
es.submit(new Runnable() {
@Override
public void run() {
try {
syncBlockClass.mehtod2();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
});
es.shutdown();
}}class MySyncBlockClass { public synchronized void mehtod1() throws InterruptedException {
TimeUnit.SECONDS.sleep(1);
System.out.println(System.currentTimeMillis() + ":method1 run.");
} public synchronized void mehtod2() throws InterruptedException {
TimeUnit.SECONDS.sleep(4);
System.out.println(System.currentTimeMillis() + ":method2 run.");
}
}// method1较method2延迟了2000ms
// 1479350064132:method2 run.
// 1479350066132:method1 run.

实例方法同步

/**
* method1 与method2等效
* 同步构造器中用括号括起来的对象叫做监视器对象
*
* @throws InterruptedException
*/
public synchronized void mehtod1() throws InterruptedException {
TimeUnit.SECONDS.sleep(1);
System.out.println(System.currentTimeMillis() + ":method1 run.");
} public synchronized void mehtod2() throws InterruptedException {
synchronized (this) {
TimeUnit.SECONDS.sleep(4);
System.out.println(System.currentTimeMillis() + ":method2 run.");
}
}

实例方法中的同步块

Static methods & Code blocks inside static methods

静态方法的同步是指同步在该方法所在的类对象上。因为在Java虚拟机中一个类只能对应一个类对象，所以同时只允许一个线程执行同一个类中的静态同步方法。

public class SyncBlockTest { public static void main(String[] args) {
ExecutorService es = Executors.newFixedThreadPool(2);
final MySyncBlockClass syncBlockClass1 = new MySyncBlockClass();
final MySyncBlockClass syncBlockClass2 = new MySyncBlockClass();
es.submit(new Runnable() {
@Override
public void run() {
try {
syncBlockClass1.mehtod1();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
});
es.submit(new Runnable() {
@Override
public void run() {
try {
syncBlockClass2.mehtod2();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
});
es.shutdown();
}}class MySyncBlockClass { public static synchronized void mehtod1() throws InterruptedException {
TimeUnit.SECONDS.sleep(1);
System.out.println(System.currentTimeMillis() + ":method1 run.");
} public static synchronized void mehtod2() throws InterruptedException {
TimeUnit.SECONDS.sleep(4);
System.out.println(System.currentTimeMillis() + ":method2 run.");
}
}// method1较method2延迟了3000ms
// 1479358310630:method1 run.
// 1479358314631:method2 run.

静态方法同步

/**
* method1 与method2等效
* 静态方法中的同步块
*
* @throws InterruptedException
*/
public static synchronized void mehtod1() throws InterruptedException {
TimeUnit.SECONDS.sleep(1);
System.out.println(System.currentTimeMillis() + ":method1 run.");
} public static synchronized void mehtod2() throws InterruptedException {
synchronized (MySyncBlockClass.class) {
TimeUnit.SECONDS.sleep(4);
System.out.println(System.currentTimeMillis() + ":method2 run.");
}
}

静态方法中的同步块

示例：

以下代码对应的Block关系如下：

synchronized(class)与 static synchronized 等效

public class SyncMethod2 {
private int value = 0;
private final Object mutex = new Object(); public synchronized int incAndGet0() {
try {
TimeUnit.SECONDS.sleep(4);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("static synchronized void incAndGet0");
return ++value;
} public int incAndGet1() {
synchronized(this){
try {
TimeUnit.SECONDS.sleep(4);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("static synchronized void incAndGet1");
return ++value;
}
} public int incAndGet2() {
synchronized(SyncMethod.class){
++value;
try {
TimeUnit.SECONDS.sleep(4);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("static synchronized void incAndGet4");
}
return 0;
} public int incAndGet3() {
synchronized(mutex){
return ++value;
}
} public static synchronized void incAndGet4() {
try {
TimeUnit.SECONDS.sleep(4);
System.out.println("static synchronized void incAndGet4");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}