Synchronization Methods in Multithreading – Java
Table of Contents
- Introduction
- Understanding Multithreading and Synchronization
- Synchronization Methods in Java
- The Synchronized Keyword in Java
- Practical Example: Synchronizing Threads with Brackets
- Conclusion
1. Introduction
In modern programming, multithreading is a key concept to achieve efficient processing, especially when tasks can be run concurrently. However, handling concurrent threads can lead to issues like data inconsistency. This is where synchronization comes into play. This chapter delves into synchronization methods in Java, a crucial technique used to ensure that threads do not interfere with each other when accessing shared resources.
Key Topics Covered:
- Basics of multithreading
- The importance of synchronization
- Different methods for synchronizing threads
2. Understanding Multithreading and Synchronization
What is Multithreading?
Multithreading refers to executing multiple threads concurrently within a program. In Java, this is accomplished by implementing the Runnable interface or extending the Thread class. However, managing these threads can be tricky as they may access shared resources, leading to unpredictable outcomes.
Why Synchronization?
Synchronization ensures that only one thread accesses a critical section of code at a time, preventing data inconsistency. The Java language provides several ways to achieve this, such as synchronized methods, blocks, and other concurrency control mechanisms like Locks.
Tabular Comparison:
| Threading Concept | Definition | When to Use |
|---|---|---|
| Multithreading | Running multiple threads simultaneously | For concurrent tasks such as file processing |
| Synchronization | Managing the access of shared resources among threads | When multiple threads access shared resources |
| Synchronized Methods | Locks the entire method for a single thread at a time | To protect a method that accesses shared resources |
3. Synchronization Methods in Java
In Java, synchronization is primarily achieved via the synchronized keyword. It can be applied to methods or code blocks to ensure mutual exclusion, preventing multiple threads from executing that block simultaneously. There are two key forms of synchronization in Java:
- Synchronized Methods: Locks the entire method.
- Synchronized Blocks: Locks a specific block of code.
Syntax for Synchronized Method:
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synchronized returnType methodName(parameters) { // Method body } |
Syntax for Synchronized Block:
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synchronized (lockObject) { // Block of code } |
4. The Synchronized Keyword in Java
The synchronized keyword ensures that only one thread executes a critical section of code at a time. This is crucial when multiple threads try to access shared data, potentially causing race conditions.
In the example provided, we use the synchronized method to ensure that two threads printing a series of brackets [ ] do not interfere with each other. This will help avoid messy outputs, such as mixing up the sequences from both threads.
5. Practical Example: Synchronizing Threads with Brackets
Let’s take a detailed look at the project file provided. The Java program synchronizes two threads using the synchronized keyword to print brackets [ ]. Without synchronization, the threads could interleave, producing incorrect output.
Code Explanation:
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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(); } } public class Main { public static void main(String[] args) { Brackets brackets = new Brackets(); new Thread(new Runnable() { @Override public void run() { for (int i = 0; i < 5; i++) { brackets.generate(); } } }).start(); new Thread(new Runnable() { @Override public void run() { for (int i = 0; i < 5; i++) { brackets.generate(); } } }).start(); } } |
Step-by-Step Explanation:
- Synchronized Method: The generate() method in the Brackets class is declared as synchronized. This ensures that only one thread can execute it at a time.
- Thread Creation: Two anonymous threads are created using the Runnable interface. Each thread calls the generate() method multiple times to print brackets.
- Thread Execution: Due to the synchronization, even though both threads run concurrently, the output will remain consistent, with one thread completing its task before the other starts.
Output:
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[ [ [ [ [ ] ] ] ] ] [ [ [ [ [ ] ] ] ] ] [ [ [ [ [ ] ] ] ] ] [ [ [ [ [ ] ] ] ] ] [ [ [ [ [ ] ] ] ] ] |
6. Conclusion
In this article, we explored synchronization methods in Java and how to use the synchronized keyword to manage multithreaded environments. Synchronization is a vital tool for ensuring data integrity when threads share resources. By understanding how synchronization works and implementing it effectively, Java developers can prevent concurrency-related issues in their applications.