How do you use happens-before relationships with a simple code example?

The happens-before relationship is a key concept in the Java Memory Model that defines the visibility of memory operations across different threads. If one action happens-before another, the results of the first action are visible to the second action. This concept is crucial for writing thread-safe code without using excessive synchronization.

Example of Happens-Before Relationship

In the example below, we have two threads: one that writes a value to a shared variable, and another that reads that value. The volatile keyword creates a happens-before relationship between the write and the read, ensuring visibility.


        import java.util.concurrent.atomic.AtomicInteger;

        public class HappensBeforeExample {
            private static AtomicInteger sharedValue = new AtomicInteger(0);
            private static volatile boolean flag = false;

            public static void main(String[] args) {
                Thread writer = new Thread(() -> {
                    sharedValue.set(42);  // Write to shared variable
                    flag = true;          // Set flag to true
                });

                Thread reader = new Thread(() -> {
                    if (flag) {          // Check flag
                        System.out.println(sharedValue.get());  // Read from shared variable
                    }
                });

                writer.start();
                reader.start();
            }
        }

How do you use happens-before relationships with a simple code example?

Example of Happens-Before Relationship

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How do you use happens-before relationships with a simple code example?

Example of Happens-Before Relationship

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