"Synchronization in Java ensures that only one thread can access a resource at a time, preventing data inconsistency in multithreaded environments."
Code Example:
class Counter {
int count = 0;
public synchronized void increment() {
count++;
}
}
public class TestSynchronization {
public static void main(String[] args) throws InterruptedException {
Counter counter = new Counter();
Thread t1 = new Thread(() -> {
for (int i = 0; i < 1000; i++) {
counter.increment();
}
});
Thread t2 = new Thread(() -> {
for (int i = 0; i < 1000; i++) {
counter.increment();
}
});
t1.start();
t2.start();
t1.join();
t2.join();
System.out.println("Count: " + counter.count);
}
}
"Synchronization ensures thread-safe access to shared resources!"
"Synchronization ensures thread-safe access to shared resources. Keep things smooth! #java #synchronization"
What is Java Synchronization?
In Java, synchronization is a way to control access to shared resources in a multi-threaded environment. It ensures that only one thread can access a shared resource (like a variable, object, or file) at a time, preventing race conditions and inconsistent data.
Why is Synchronization Needed?
In a multi-threaded application, multiple threads may try to access and modify the same resource simultaneously. This can lead to:
Data Inconsistency:
Example: Two threads updating a shared counter simultaneously may result in incorrect values.Unpredictable Behaviour:
Without synchronization, the execution order of threads can vary, leading to unpredictable results.
Synchronization ensures thread-safe access by locking the resource for one thread at a time.
How Does Synchronization Work?
Locks and Monitors:
Every object in Java has an intrinsic lock or monitor.
When a thread enters a synchronized block or method, it acquires the lock on the object.
Other threads must wait until the lock is released.
Thread Ownership:
Only the thread holding the lock can execute synchronized code.
The lock is released when the thread exits the synchronized block or method.
Ways to Achieve Synchronization in Java
1. Synchronized Methods
Declares an entire method as synchronized.
Only one thread can execute this method on the object at a time.
Example:
java
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public synchronized void increment() {
counter++;
}
Here, only one thread can increment the counter at any given time.
2. Synchronized Blocks
Synchronizes only a specific part of a method.
Provides more fine-grained control compared to synchronized methods.
Example:
java
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public void increment() {
synchronized (this) { // Locking the current object
counter++;
}
}
This allows other non-synchronized parts of the method to run while protecting the critical section.
3. Static Synchronization
Synchronizes static methods or blocks, locking the class object.
Example:
java
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public static synchronized void log() {
// Critical section for static data
}
Practical Example of Synchronization
Imagine a banking system where two threads are trying to withdraw money from the same account:
Without Synchronization:
class Account {
private int balance = 1000;
public void withdraw(int amount) {
if (balance >= amount) {
System.out.println(Thread.currentThread().getName() + " is withdrawing " + amount);
balance -= amount;
System.out.println("Remaining balance: " + balance);
} else {
System.out.println("Insufficient funds!");
}
}
}
public class Main {
public static void main(String[] args) {
Account account = new Account();
Thread t1 = new Thread(() -> account.withdraw(800), "Thread-1");
Thread t2 = new Thread(() -> account.withdraw(800), "Thread-2");
t1.start();
t2.start();
}
}
Problem: Both threads might check the balance at the same time, leading to incorrect deductions.
With Synchronization:
class Account {
private int balance = 1000;
public synchronized void withdraw(int amount) { // Adding synchronization
if (balance >= amount) {
System.out.println(Thread.currentThread().getName() + " is withdrawing " + amount);
balance -= amount;
System.out.println("Remaining balance: " + balance);
} else {
System.out.println("Insufficient funds!");
}
}
}
public class Main {
public static void main(String[] args) {
Account account = new Account();
Thread t1 = new Thread(() -> account.withdraw(800), "Thread-1");
Thread t2 = new Thread(() -> account.withdraw(800), "Thread-2");
t1.start();
t2.start();
}
}
Solution: Synchronization ensures only one thread can execute the withdraw method at a time, preventing data inconsistencies.
Key Points to Remember
Cost of Synchronization:
Synchronization adds overhead and can slow down performance if overused. Use it only for critical sections.Deadlocks:
Poorly managed synchronization can lead to deadlocks, where threads are stuck waiting for each other indefinitely.Atomic Variables & Locks:
For more advanced synchronization, Java provides tools like ReentrantLock, ReadWriteLock, and atomic variables in the java.util.concurrent package.
Summary
Java synchronization ensures thread-safe access to shared resources by using locks. It can be implemented using synchronized methods, synchronized blocks, or static synchronization. Use it judiciously to avoid performance bottlenecks or deadlocks.
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