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Check if following code is threadsafe for retrieving an integer value from a Queue?

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Pragya Keshap answered on February 4, 2023 Popularity 1/10 Helpfulness 1/10

answer Check if following code is threadsafe for retrieving an integer value from a Queue?

Check if following code is threadsafe for retrieving an integer value from a Queue?

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public class QueueCheck {

Queue queue;

public Integer getNextInt() {

Integer retVal = null;

synchronized (queue) {

try {

while (queue.isEmpty()) {

queue.wait();

}

} catch (InterruptedException e) {

e.printStackTrace();

}

synchronized (queue) {

retVal = queue.poll();

if (retVal == null) {

System.err.println("retVal is null");

throw new IllegalStateException(); }

}

return retVal;

}

In the above code Queue is used as object monitor to handle

concurrency issues. But it may not behave correctly in a multithreading scenario.

There are two separate synchronized blocks in above code. In case

two threads are woken up simultaneously by another thread, both

threads will enter one after in the second synchronized block.

Only one of the two threads will get new value from the queue and

make it empty. The second thread will poll on an empty queue and it

will not get any non-null return value.

class Counter {
 
    // Creating a variable of
    // class type AtomicInteger
    AtomicInteger count
        = new AtomicInteger();
 
    // Defining increment() method
    // to change value of
    // AtomicInteger variable
    public void increment()
    {
        count.incrementAndGet();
    }
}
 
public class TestCounter {
    public static void main(
        String[] args) throws Exception
    {
 
        // Creating an instance of
        // Counter class
        Counter c = new Counter();
 
        // Creating an instance t1 of
        // Thread class
        Thread t1 = new Thread(
            new Runnable() {
                public void run()
                {
                    for (int i = 1; i <= 2000; i++) {
                        c.increment();
                    }
                }
            });
 
        // Creating an instance t2
        // of Thread class
        Thread t2 = new Thread(
            new Runnable() {
                public void run()
                {
                    for (int i = 1; i <= 2000; i++) {
                        c.increment();
                    }
                }
            });
 
        // Calling start() method with t1 and t2
        t1.start();
        t2.start();
 
        // Calling join method with t1 and t2
        t1.join();
        t2.join();
 
        System.out.println(c.count);
    }
}

https://www.geeksforgeeks.org/thread-safety-and-how-to-achieve-it-in-java/

Popularity 1/10 Helpfulness 1/10 Language java

Source: Grepper

Tags: integer java

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Contributed on Feb 04 2023

Pragya Keshap

0 Answers Avg Quality 2/10

Check if following code is threadsafe for retrieving an integer value from a Queue?

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