What is the purpose of the synchronized block in Java?
Table of Contents
- Introduction
- Why Use Synchronized Block in Java?
- Practical Examples of Using Synchronized Block
- Conclusion
Introduction
In Java, a synchronized block is used to prevent multiple threads from accessing a shared resource simultaneously, ensuring thread safety and data consistency in concurrent applications. When multiple threads try to modify shared data at the same time, race conditions can occur, leading to inconsistent results. Synchronization in Java solves this issue by allowing only one thread to access a particular block of code at a time.
Why Use Synchronized Block in Java?
1. Ensuring Thread Safety
The primary purpose of the synchronized block in Java is to ensure thread safety. When multiple threads work on shared data, there's a risk of data inconsistency. The synchronized block prevents multiple threads from entering critical sections of code simultaneously, ensuring that only one thread can execute a given portion of the code.
Example:
In this example, the synchronized(this) block ensures that only one thread can modify the count variable at a time, preventing race conditions and ensuring that the final count is consistent.
2. Optimizing Performance with Fine-Grained Synchronization
While synchronizing entire methods is possible in Java, using a synchronized block allows for fine-grained synchronization, meaning that only the critical section of the code (the part where data is modified) is locked. This improves the performance by allowing other parts of the method to run concurrently without being blocked.
Example:
Here, only the section of code where the balance is modified is synchronized, allowing other non-critical operations (like reading the balance) to run concurrently without locking the entire method.
3. Locking on Custom Objects
In Java, you can synchronize on any object, not just the current instance (this). This allows you to synchronize multiple threads on a specific object that represents the shared resource.
Example:
In this example, synchronization occurs on a custom lock object lock, ensuring that the critical section is properly protected. This is useful when you want to synchronize access to a resource across multiple methods or objects.
Practical Examples of Using Synchronized Block
Example 1: Thread-Safe Counter
This ensures that the counter is incremented correctly in a multi-threaded environment.
Example 2: ATM Withdrawal System
This example demonstrates how multiple users can safely withdraw money from the same ATM without causing inconsistent states.
Conclusion
The synchronized block in Java is a powerful tool for managing concurrency, ensuring that critical sections of your code are accessed by only one thread at a time. By using synchronized blocks effectively, you can prevent race conditions, maintain data integrity, and improve the performance of your multi-threaded Java applications. It's crucial to apply synchronization carefully to avoid performance bottlenecks caused by excessive locking.