CODEWITHSUNDEEP
javamultithreadingsynchronized-block
Curious
Curious

Reputation: 921

synchronized(this) block within the synchronized method

The following is the code snippet from java concurrency in practice book while discussing open calls. The point I'm not getting is that the way setLocation method is declared, it is already synchronized and again calling the synchronized(this) block within the same method, why this ? Is it type mistake ? The synchronized method already holds the lock on this method then why again for the same object ?

   @ThreadSafe 
    class Taxi { 
        @GuardedBy("this") private Point location, destination; 
        private final Dispatcher dispatcher; 
        ... 
        public synchronized Point getLocation() { 
            return location; 
        } 
        public synchronized void setLocation(Point location) { 
            boolean reachedDestination; 
            synchronized  (this) { 
                this.location = location; 
                reachedDestination = location.equals(destination); 
            } 
            if (reachedDestination) 
                dispatcher.notifyAvailable(this); 
        } 
    }

Upvotes: 0

Views: 76

Answers (1)

JB Nizet
JB Nizet

Reputation: 691685

It's an error in the book. See the errata

In Listing 10.6, Taxi.setLocation should not be a synchronized method. (The synchronized block in its body is correct, however.)

Upvotes: 5

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