The volatile keyword is used to indicate that the value of a variable can be changed simultaneously with multiple formulas. It simultaneously plays an important role by promising shared change to ensure visibility. Here are the main parts and their implications in using volatile.

 

Visibility Guarantee

If a variable is declared volatile, any read and write operations on that variable are atomic. This means that changes made by one thread to a volatile variable are immediately recognized by another thread. Without flexibility, threads can cache changes or optimize their reads and writes so that changes introduced by one thread are not immediately visible to others

 

No Atomicity or Compound Actions

It is important to note that the volatile does not cause atomization for compound reactions. For example, incrementing a volatile variable (count++) is not atomic because it involves a read-modify-write operation, which can be canceled by other threads

 

Memory Ordering

Using volatile also ensures that read and write operations on a variable are not reconfigured by the compiler or CPU. This is especially important in multiprocessor systems where threads can operate on different CPUs with their own cache. If it is not confusing, a formula can read an outdated value from its cache, resulting in incorrect behavior.

 

Use Cases for volatile

 

Flag Variables- volatile is often used for Boolean flags that control the operation between threads.

public class SharedResource {
   private volatile boolean flag = false;
   public void setFlag() {
       flag = true;
   }
   public boolean isFlagSet() {
       return flag;
   }
}

 

In this example, the flag is marked as volatile to ensure that a change made by one thread (setting the flag to true) is immediately recognized by other threads.

 

Status Flags in Thread Coordination 

This is useful to identify between threads where one thread sets the flag and another checks it.

public class Worker extends Thread {
   private volatile boolean running = true;
   @Override
   public void run() {
       while (running) {
           // do work
       }
   }
   public void stopWorker() {
       running = false;
   }
}

 

Here the running flag is used to control the loop in the Worker thread. Setting running to false in stopWorker() will stop the thread immediately due to the visibility promised by volatile.

 

When Not to Use volatile

Mutual Exclusion- volatile does not provide mutual exclusion, so it is not suitable for cases where variables shared by multiple threads need to be updated atomically.

Performance Considerations- Although volatile ensures visibility and configurability guarantees, overuse of volatility can affect performance due to frequent cache invalidations between threads

 

The volatile keyword in Java ensures that changes to a variable made by one thread are immediately recognized by another thread. To ensure proper thread safety and synchronization in concurrent programming, especially for flag variables and simple status pointers in threads it is important to understand its uses and limitations and it is important to create proper and efficient concurrent Java applications.

 

Also, Read: Differentiate between checked and unchecked exceptions in Java with examples.