Static synchronization is a form of synchronization in computer programming where synchronization is achieved through the use of static variables and methods. Static variables and methods are those that belong to a class rather than to a specific instance of that class.
In static synchronization, the synchronization is achieved by applying the synchronized keyword to a static method or a block of code that accesses static variables. When a thread attempts to execute a synchronized static method or block of code, it must first acquire the lock associated with the class object. This lock is held by the first thread that acquires it, and any subsequent threads that attempt to acquire the lock must wait until the lock is released.
Static synchronization can be useful in situations where multiple threads are accessing shared resources that are static variables or methods. By using static synchronization, the threads can be coordinated to avoid conflicts and ensure that the shared resources are accessed in a mutually exclusive manner.
However, it is important to note that static synchronization can have a negative impact on performance, as it can lead to contention for the lock associated with the class object. It is also important to use static synchronization with caution, as it can lead to deadlocks if not used properly.
Problem without static synchronization:
Without static synchronization, multiple threads accessing shared resources, such as shared variables or methods, can lead to race conditions and other synchronization issues. Race conditions occur when the output of a program depends on the sequence or timing of events, such as the order in which threads access shared resources.
For example, consider a scenario where multiple threads access a shared variable without any synchronization mechanism in place. If one thread reads the variable while another thread is in the process of updating it, the first thread may get an inconsistent value that does not accurately reflect the current state of the variable. This can lead to incorrect program behavior, data corruption, or even crashes.
Another problem that can occur without static synchronization is when multiple threads try to access or modify the same shared resource simultaneously. This can result in thread interference, data races, and other synchronization issues that can cause incorrect program behavior, unexpected output, or even program crashes.
In summary, without static synchronization, concurrent access to shared resources can lead to race conditions, thread interference, data races, and other synchronization issues that can cause incorrect program behavior and potential system failures.
Example of Static Synchronization:
Here is an example of static synchronization in Java:
public class Counter {
private static int count = 0;
public static synchronized void increment() {
count++;
}
public static synchronized int getCount() {
return count;
}
}
In this example, the Counter class has a static variable count that represents a shared resource. The class also has two static methods, increment() and getCount(), that access and modify the count variable.
The increment() and getCount() methods are both declared as synchronized, which means that only one thread can execute these methods at a time. This ensures that the shared count variable is accessed and modified in a mutually exclusive manner, preventing race conditions and other synchronization issues.
By using static synchronization in this example, multiple threads can safely increment and retrieve the shared count variable without causing synchronization issues.
Example of static synchronization by Using the anonymous class:
Here’s an example of using static synchronization with an anonymous class in Java:
public class Counter {
private static int count = 0;
public static void increment() {
synchronized (Counter.class) {
count++;
}
}
public static int getCount() {
synchronized (Counter.class) {
return count;
}
}
public static void main(String[] args) {
// Create multiple threads to increment the counter
for (int i = 0; i < 10; i++) {
new Thread(new Runnable() {
public void run() {
for (int j = 0; j < 100; j++) {
Counter.increment();
}
}
}).start();
}
// Wait for all threads to finish
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
// Print the final value of the counter
System.out.println("Final count: " + Counter.getCount());
}
}
In this example, the Counter class has a static variable count that represents a shared resource. The increment() and getCount() methods use a synchronized block with the Counter.class object as the lock object.
To demonstrate the usage, the main() method creates 10 threads that increment the counter 100 times each. The final value of the counter is then printed.
By using static synchronization with an anonymous class in this example, multiple threads can safely access and modify the shared count variable without causing synchronization issues. The use of an anonymous class is just a way to create the threads, and it does not affect the static synchronization mechanism used to access the shared resource.
Synchronized block on a class lock:
In Java, a synchronized block can be used with a class lock to provide static synchronization. A class lock is associated with the class object and is acquired by a thread when it enters a synchronized block on the class object.
Here is an example of using a synchronized block with a class lock:
public class MyClass {
private static int count = 0;
public static void increment() {
synchronized(MyClass.class) {
count++;
}
}
public static int getCount() {
synchronized(MyClass.class) {
return count;
}
}
}
In this example, the increment() and getCount() methods use a synchronized block with the MyClass.class object as the lock object. This ensures that only one thread can execute the block at a time, preventing race conditions and other synchronization issues.
When a thread enters a synchronized block on the MyClass.class object, it acquires the class lock associated with the MyClass class. The lock is released when the thread exits the block. Other threads that attempt to enter a synchronized block on the same object will have to wait until the lock is released before they can execute the block.
Using a synchronized block on a class lock provides a way to synchronize access to static variables and methods in a thread-safe manner. By using a class lock, multiple threads can safely access and modify the shared variables and methods without causing synchronization issues.