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Synchronization in Java

Introduction

Java, a powerful and versatile programming language, provides built-in support for multithreaded programming. A multithreaded program contains two or more parts that can run concurrently. Each part of such a program is called a thread, and each thread defines a separate path of execution. But what happens when these threads need to interact or share resources? That's where synchronization comes into play.

What is Synchronization?

Synchronization in Java is the capability to control the access of multiple threads to a shared resource. Without synchronization, it's possible for one thread to modify a shared variable while another thread is in the process of using or updating that same variable. This usually leads to significant errors.

Why Use Synchronization?

Imagine a situation where multiple threads are working on the same object. In such a case, there's a possibility that more than one thread has changed the property of the object. This leads to data inconsistency. To overcome these issues, we use synchronization in Java.

How Does Synchronization Work?

Java uses a concept known as monitors to handle synchronization. A monitor is basically a guardian in a sense. Its job is to watch over a sequence of code, allowing only one thread to execute the code at a time.

Synchronized Methods

In Java, you can declare methods as synchronized. Only one thread at a time can access a synchronized method of an object. If a thread is executing a synchronized method, all other threads that invoke synchronized methods for the same object will be blocked until the first thread is done with the object.

Here is an example of a synchronized method:

public synchronized void showNumbers() {
    // Code here
}

In the above example, showNumbers() is a synchronized method. This means that if one thread is executing this method, no other thread can call this method—or any other synchronized method—for the same object.

Synchronized Statements

Synchronized statements (also known as synchronized blocks) are similar to synchronized methods, but offer two advantages:

  • They reduce the level of granularity, allowing you to protect just the portion of a method that manipulates the sensitive data, rather than the entire method.
  • They can specify the object that provides the intrinsic lock.

Here is an example of a synchronized statement:

public void add(String str) {
    synchronized(this) {
        arrayList.add(str);
    }
}

In the above example, the synchronized statement is only locking the code that is manipulating arrayList.

Conclusion

Synchronization is a vital concept in multithreaded programming. It helps us to avoid data inconsistency and thread interference issues by allowing only one thread to access the shared resource at a time. It's important to remember, however, that improper use of synchronization can lead to issues like deadlock, starvation, and thread-thrashing. Therefore, it's crucial to use synchronization judiciously to ensure the smooth execution of our multithreaded programs.