Are primitive datatypes thread-safe in Java

Are the primitive data types like int & short thread-safe in Java? I have executed the following code and couldn't see expected result 500 some times.

public class SampleThree extends Thread
{
    static long wakeUpTime = System.currentTimeMillis() + (1000*20);
    static int inT;
    public static void main(String args[])
    {
        System.out.println("initial:" + inT);
        for(int i=0; i<500; i++)
            new SampleThree().start();
        try {
            Thread.sleep(wakeUpTime - System.currentTimeMillis() + (1000*30));
            System.out.println("o/p:" + inT);
        }
        catch(Exception e){
            e.printStackTrace();
        }
    }

    public void run()
    {
        try {
            long s = wakeUpTime - System.currentTimeMillis();
            System.out.println("will sleep ms: " + s);
            Thread.sleep(s);
            inT++; // System.out.println(inT);
        }
        catch(Exception e) {
            e.printStackTrace();
        }
    }
}

Here concurrently 500 thread will update the int variable inT. Main thread after waiting for concurrent update to be completed, prints inT value.

Find similar example here

There are three ways in which they're not safe:

long and double aren't even guaranteed to be updated atomically (you could see half of a write from a different thread)
The memory model doesn't guarantee that you'll see the latest updates from one thread in another thread, without extra memory barriers of some kind
The act of incrementing a variable isn't atomic anyway

Use AtomicInteger etc for thread-safe operations.

Parvin Gasimzade

Primitive types are not thread safe. Check this tutorial.

I would suggest using classes in java.util.concurrent.atomic. They are designed for thread-safety and in some cases the JVM can take advantage of hardware features to optimize.

来源：https://stackoverflow.com/questions/9278764/are-primitive-datatypes-thread-safe-in-java

标签

java

thread-safety

primitive