In Java, synchronization is the process of coordinating the execution of multiple threads to ensure that they don’t interfere with each other. When two or more threads access shared data or resources concurrently, they can produce unexpected results due to race conditions and other concurrency issues. Synchronization allows us to avoid these problems by ensuring that only one thread can access a shared resource at a time.
In Java, we can synchronize code blocks or methods using the synchronized keyword. When a method or block is synchronized, only one thread can execute it at a time, and all other threads are blocked until the lock is released. Here’s an example of synchronizing a method:
public class Counter {
private int count;
public synchronized void increment() {
count++;
}
public synchronized void decrement() {
count--;
}
public synchronized int getCount() {
return count;
}
}In this example, we have a Counter class that has three methods: increment, decrement, and getCount. Each of these methods is synchronized using the synchronized keyword, which ensures that only one thread can execute them at a time. This prevents race conditions and other concurrency issues that could arise if multiple threads tried to modify or access the count variable concurrently.
Another way to synchronize code in Java is to use the Lock and Condition interfaces. These interfaces provide a more fine-grained way to control access to shared resources and allow for more flexibility in the way that threads are synchronized. Here’s an example of using Lock and Condition:
import java.util.concurrent.locks.*;
public class Buffer {
private Lock lock;
private Condition condition;
private int[] buffer;
private int count;
public Buffer(int size) {
lock = new ReentrantLock();
condition = lock.newCondition();
buffer = new int[size];
count = 0;
}
public void put(int value) throws InterruptedException {
lock.lock();
try {
while (count == buffer.length) {
condition.await();
}
buffer[count] = value;
count++;
condition.signalAll();
} finally {
lock.unlock();
}
}
public int take() throws InterruptedException {
lock.lock();
try {
while (count == 0) {
condition.await();
}
int value = buffer[count - 1];
count--;
condition.signalAll();
return value;
} finally {
lock.unlock();
}
}
}In this example, we have a Buffer class that represents a shared buffer that can be used to exchange data between threads. The put and take methods are used to add and remove values from the buffer, respectively. These methods are synchronized using the Lock and Condition interfaces, which allow for more fine-grained control over the synchronization process.
Synchronization is an important concept in Java and is essential for developing concurrent applications that work correctly and efficiently. By understanding the principles of synchronization and how to use the synchronization mechanisms provided by Java, you can write more robust and reliable code that can take advantage of the benefits of concurrency.