Clash Royale CLAN TAG#URR8PPP

thread synchronization problem (with updating a variable sum)

When I want to update with either synchronized keyword or lock, it works when the sum variable is int but not when it is an Integer object.

code looks like this -

public class TestSynchronized
private Integer sum = new Integer(0);

public static void main(String args)
TestSynchronized test = new TestSynchronized();
System.out.println("The sum is :" + test.sum);


public TestSynchronized()
ExecutorService executor = Executors.newFixedThreadPool(1000);

for (int i = 0; i <=2000; i++)
executor.execute(new SumTask());


executor.shutdown();

while(!executor.isTerminated())



class SumTask implements Runnable
Lock lock = new ReentrantLock();

public void run()
lock.lock();

int value = sum.intValue() + 1;
sum = new Integer(value);

lock.unlock(); // Release the lock






Lock lock = new ReentrantLock();

1 Answer
1

The problem is that you've separate locks for each of the SumTask objects. These objects should share the locks instead.

locks

SumTask

locks

Create a lock object once in TestSynchronized() method. This should be shared by all the new SumTask(lock) objects.

lock

TestSynchronized()

new SumTask(lock)

So your SumTask class would look like:

SumTask

class SumTask implements Runnable
Lock lock;

public SumTask(Lock commonLock)
this.lock = commonLock;


public void run()
lock.lock();

int value = sum.intValue() + 1;
sum = new Integer(value);

lock.unlock(); // Release the lock





And don't forget to create a commonLock object in TestSynchronized() method:

commonLock

TestSynchronized()

Lock lock = new ReentrantLock();

executor.execute(new SumTask(commonLock));


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