Synchronization Blocks in Java
Table of Contents
- Introduction
- What are Synchronization Blocks in Java?
- Synchronization Blocks Based on Objects
- Pros and Cons of Synchronization Blocks
- Conclusion
Introduction
In Java, when multiple threads access shared resources, synchronization is essential to prevent data inconsistency and potential race conditions. One such mechanism to ensure thread safety is using synchronization blocks. This article explores synchronization blocks, particularly those based on objects, by leveraging real-world examples.
Java provides multiple ways to synchronize blocks of code, such as using methods or blocks inside code that need protection. This article will use a practical example from a Java project where brackets are generated using synchronization.
What are Synchronization Blocks in Java?
Synchronization in Java is a technique used to control the access of multiple threads to shared resources. When a shared resource is accessed by multiple threads simultaneously, issues such as race conditions and data inconsistency may arise. Synchronization blocks allow you to specify portions of code that need exclusive access to a particular thread.
Use Case of Synchronization
Consider a scenario where multiple threads are printing opening and closing brackets ( [ ]). If two threads try to access the printing mechanism simultaneously, the output could be incorrect. Synchronization ensures that only one thread executes the bracket generation at a time.
Benefits of Synchronization Blocks
| Benefit | Description |
|---|---|
| Thread safety | Ensures that only one thread can execute the block of code. |
| Avoidance of race conditions | Prevents conflicts and ensures data integrity. |
| Precision control | You can synchronize only the code that needs protection. |
Synchronization Blocks Based on Objects
Synchronization blocks allow you to lock a specific object for exclusive access by one thread at a time. In our example, we synchronize the printing of brackets, ensuring that one thread completes its task before the next begins.
Code Example: Brackets Class and Thread Execution
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class Brackets { synchronized public void generate() { for (int i = 1; i <= 20; i++) { if (i <= 10) { System.out.print('['); } else { System.out.print(']'); } } System.out.println(); } } |
In the above code:
- We have a class Brackets with a synchronized method generate(). This method prints 10 opening brackets followed by 10 closing brackets.
- The synchronized keyword ensures that only one thread can execute the method at a time, preventing other threads from accessing it simultaneously.
Code Walkthrough
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public class Main { public static void main(String[] args){ Brackets brackets = new Brackets(); // Thread 1 new Thread(new Runnable() { @Override public void run() { for (int i = 0; i < 5; i++) { brackets.generate(); } } }).start(); // Thread 2 new Thread(new Runnable() { @Override public void run() { for (int i = 0; i < 5; i++) { brackets.generate(); } } }).start(); } } |
This Main class creates two threads. Both threads attempt to invoke the generate() method of the Brackets class. Because generate() is synchronized, one thread must wait for the other to finish before proceeding.
Key Terminology
- Synchronized block: A portion of code locked so only one thread can execute it.
- Race condition: A scenario where multiple threads access shared resources, leading to unpredictable results.
Pros and Cons of Synchronization Blocks
| Pros | Cons |
|---|---|
| Thread Safety | Can lead to performance issues due to thread blocking. |
| Simplifies Thread Synchronization | May cause deadlocks if not used carefully. |
| Granular Control | Can make debugging more difficult. |
Conclusion
In this article, we explored how synchronization blocks based on objects can be used to ensure thread safety in Java. By understanding synchronization blocks, developers can prevent race conditions and ensure that critical sections of code are executed by one thread at a time. This technique is invaluable when working with concurrent threads and shared resources.