Java Synchronized

Understanding Java Synchronized

The synchronized keyword in Java is a fundamental tool used to ensure thread safety by controlling access to critical sections of code. It is essential when multiple threads might access shared resources concurrently, potentially leading to inconsistent data states or corrupt data.

When a method or block of code is declared as synchronized, a lock is obtained on the object, allowing only one thread to execute that code block at a time. This prevents race conditions and ensures that data integrity is maintained.

Synchronized Methods

A synchronized method is one way to apply the synchronized keyword. In this case, the lock is associated with the object instance for non-static methods or the class object for static methods. Here is an example of a synchronized method:

In this example, both increment and getCount methods are synchronized, meaning that when a thread calls one of these methods, other threads must wait for the lock to be released before accessing the same object instance's synchronized methods.

Synchronized Blocks

Synchronized blocks offer more granular control over synchronization by allowing the developer to define a specific object as the lock. This is useful for synchronizing only the critical sections of code instead of entire methods. Here's how a synchronized block looks:

In this example, the lock object is used to synchronize access to the increment and getCount operations, ensuring that only one thread can execute these sections at a time.

Best Practices with Synchronized

While synchronized is a powerful keyword, it must be used judiciously to avoid common pitfalls such as deadlocks and performance bottlenecks. Here are some best practices:

• Only synchronize the smallest possible block of code necessary.
• Minimize the number of synchronized blocks to reduce contention.
• Avoid nested synchronized blocks to prevent deadlocks.
• Consider using higher-level concurrency utilities from java.util.concurrent package for more complex scenarios.