<Back
A synchronized method is a shorthand for a synchronized block that spans an entire method body, and whose lock is the object on which the method is being invoked. Every java object can implicitly act as a lock for purpose of synchronization. When thread A attempts to acquire a lock held by thread B, A must wait, or block, until B releases it.
A synchronized method is a shorthand for a synchronized block that spans an entire method body, and whose lock is the object on which the method is being invoked. Every java object can implicitly act as a lock for purpose of synchronization. When thread A attempts to acquire a lock held by thread B, A must wait, or block, until B releases it.
How to fix it?
public class BasicSynchronizer implements Runnable{
private static SynchDemo demo = new SynchDemo();
/*
private SynchDemo demo = new SynchDemo();
*/
public static void main(String ... args) {
for(int i = 0; i < 5; i++) {
Thread th = new Thread(new BasicSynchronizer());
th.start();
}
}
public void run() {
demo.sayHello();
}
}
class SynchDemo {
public synchronized void sayHello() {
System.out.println(Thread.currentThread().getName() + " start");
System.out.println(Thread.currentThread().getName() + " Hello");
System.out.println(Thread.currentThread().getName() + " end");
}
}
concurrency>javac BasicSynchronizer.java
concurrency>java BasicSynchronizer
Thread-1 start
Thread-4 start
Thread-4 Hello
Thread-3 start
Thread-0 start
Thread-0 Hello
Thread-0 end
Thread-2 start
Thread-2 Hello
Thread-2 end
Thread-3 Hello
Thread-3 end
Thread-4 end
Thread-1 Hello
Thread-1 end
concurrency>
Hint:
"A synchronized method is a shorthand for a synchronized block that spans an entire method body, and whose lock is the object on which the method is being invoked. "
What Objects act as the lock for synchronized method sayHello()?
Second Hint:
The SynchDemo objects act as the lock for synchronized method sayHello().
How many SynchDemo objects are created in the program?
Every time new BasicSynchronizer() is called, a new SynchDemo object is created, each thread hold a different lock, they didn't share the same lock.
