Java 中的对象级锁定
java 中的每个对象都有一个唯一的锁。每当我们使用同步关键字时，只有锁的概念会出现在图片中。如果线程想在给定对象上执行同步方法。首先，它必须获得该对象的锁。一旦线程获得了锁，那么它就被允许对该对象执行任何同步的方法。一旦方法执行完成，线程会自动释放锁。内部获取和释放锁由 JVM 负责，程序员不对这些活动负责
当我们希望同步一个非静态方法或非静态代码块时，对象级锁是一种机制，这样只有一个线程能够在类的给定实例上执行代码块。
如果线程想在给定对象上执行同步方法。首先，它必须获得该对象的锁。一旦线程获得了锁，那么它就被允许对该对象执行任何同步的方法。一旦方法执行完成，线程会自动释放锁。内部获取和释放锁由 JVM 负责，程序员不对这些活动负责。
方法:我们可以通过不同的方式将对象锁定在线程中，如下所示:
方法 1:
public class GeekClass
{
public synchronized void GeekMethod(){}
}
方法二:
public class GeekClass
{
public void GeekMethod(){
synchronized (this)
{
// other thread safe code
}
}
}
方法 3:
public class DemoClass
{
private final Object lock = new Object();
public void demoMethod(){
synchronized (lock)
{
// other thread safe code
}
}
}
示例:
Java 语言(一种计算机语言，尤用于创建网站)
// Java program to illustrate
// Object lock concept
// Class
// Extending Runnable interface
class Geek implements Runnable {
// Method of this class
public void run() { Lock(); }
// Synchronization of non-static methods
// (object lock) as different synchronized
// non-static methods are called in both threads
// Then both threads need to acquire the object lock
// After one is acquired, the other thread must wait
// for one thread to finish the executing
// before the other thread starts to execute.
public void Lock()
{
System.out.println(
Thread.currentThread().getName());
synchronized (this)
{
System.out.println(
"in block "
+ Thread.currentThread().getName());
System.out.println(
"in block "
+ Thread.currentThread().getName()
+ " end");
}
}
// Main driver method
public static void main(String[] args)
{
// Creating an object of above class
// in the main() method
Geek g = new Geek();
// Sharing the same object across two Threads
// Here, t1 takes g
Thread t1 = new Thread(g);
// Here, t2 takes g
Thread t2 = new Thread(g);
// Creating another object of above class
Geek g1 = new Geek();
// Here, t3 takes g1
Thread t3 = new Thread(g1);
// setname() method is used to change
// name of the thread
t1.setName("t1");
t2.setName("t2");
t3.setName("t3");
// start() method beginning the execution of threads
// as JVM calls the run() method of thread
t1.start();
t2.start();
t3.start();
}
}
Output
t1
t3
t2
in block t1
in block t3
in block t1 end
in block t2
in block t2 end
in block t3 end
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