Java - Static Synchronization

Synchronization is a way that establishes cooperation between multiple threads trying to access shared resources. It is necessary for reliable thread interaction and is done using the 'synchronized' keyword. Here, threads are small sub processes of a big operation. In this article, we are going to learn static synchronization and how they manage threads so that they can work efficiently.

Multithreading

Multithreading is a feature of Java programming language that allows us to perform multiple operations simultaneously. In it, the operation gets divided into multiple smaller parts called a thread. Each thread performs one independent task without affecting the other thread’s performance. The main benefit of multithreading is the optimal use of resources like CPU and it boosts the execution time of allocated operations.

Synchronization

The threads are executed in an asynchronous manner therefore, it is impossible to predict how they are going to interact. Sometimes, several threads may try to access a single resource, then a problem arises because it might create a faulty result of the allocated task. At this time, Synchronization comes into the picture and ensures that a single thread can access the given resource at one time. This is possible because of the lock object that guards the synchronized region. When a thread enters that region, the lock gets assigned to it and it releases the lock after executing its task. Till the resources are busy other threads wait in a queue for their turn.

Static Synchronization in Java

When we use this type of synchronization then, if a thread is in the static synchronized region, all other threads trying to access this region will be blocked. Since static methods belong to the class therefore, static synchronization applies class level lock.

Syntax of Static Synchronization

static synchronized returnType nameOfMethod( Type parameters) {
	// code
} 

Here returnType may be void or any primitive data type. parameters contains name of the variable followed by datatype.

Multithreading Without Static Synchronization

Here is a simple example which may or may not print counter value in sequence and every time we run it, it produces a different result based on CPU availability to a thread.

Example of Multithreading Without Static Synchronization

package com.tutorialspoint;

class PrintDemo {
   public static void printCount() {
      try {
         for(int i = 5; i >  0; i--) {
            Thread.sleep(50);
            System.out.println("Counter   ---   "  + i );
         }
      } catch (Exception e) {
         System.out.println("Thread  interrupted.");
      }
   }
}

class ThreadDemo extends Thread {
   private Thread t;
   private String threadName;

   ThreadDemo( String name) {
      threadName = name;
   }
   
   public void run() {
      PrintDemo.printCount();
      System.out.println("Thread " +  threadName + " exiting.");
   }

   public void start () {
      System.out.println("Starting " +  threadName );
      if (t == null) {
         t = new Thread (this, threadName);
         t.start ();
      }
   }
}

public class TestThread {
   public static void main(String args[]) {
      ThreadDemo t1 = new ThreadDemo( "Thread - 1 " );
      ThreadDemo t2 = new ThreadDemo( "Thread - 2 " );

      t1.start();
      t2.start();

      // wait for threads to end
         try {
         t1.join();
         t2.join();
      } catch ( Exception e) {
         System.out.println("Interrupted");
      }
   }
}

This produces a different result every time you run this program −

Output

Starting Thread - 1 
Starting Thread - 2 
Counter   ---   5
Counter   ---   5
Counter   ---   4
Counter   ---   4
Counter   ---   3
Counter   ---   3
Counter   ---   2
Counter   ---   2
Counter   ---   1
Counter   ---   1
Thread Thread - 1  exiting.
Thread Thread - 2  exiting.

Multithreading With Static Synchronization

Here is the same example which prints counter value in sequence and every time we run it, it produces the same result. W've put synchronized keyword over a method this time so that complete method is locked as per the object during method execution.

Example of Multithreading With Static Synchronization

package com.tutorialspoint;

class PrintDemo {
   public static synchronized void printCount() {
      try {
         for(int i = 5; i >  0; i--) {
            Thread.sleep(50);
            System.out.println("Counter   ---   "  + i );
         }
      } catch (Exception e) {
         System.out.println("Thread  interrupted.");
      }
   }
}

class ThreadDemo extends Thread {
   private Thread t;
   private String threadName;

   ThreadDemo( String name) {
      threadName = name;
   }
   
   public void run() {
      PrintDemo.printCount();
      System.out.println("Thread " +  threadName + " exiting.");
   }

   public void start () {
      System.out.println("Starting " +  threadName );
      if (t == null) {
         t = new Thread (this, threadName);
         t.start ();
      }
   }
}

public class TestThread {
   public static void main(String args[]) {
      ThreadDemo t1 = new ThreadDemo( "Thread - 1 " );
      ThreadDemo t2 = new ThreadDemo( "Thread - 2 " );

      t1.start();
      t2.start();

      // wait for threads to end
         try {
         t1.join();
         t2.join();
      } catch ( Exception e) {
         System.out.println("Interrupted");
      }
   }
}

This produces following result every time you run this program −

Output

Starting Thread - 1 
Starting Thread - 2 
Counter   ---   5
Counter   ---   4
Counter   ---   3
Counter   ---   2
Counter   ---   1
Thread Thread - 1  exiting.
Counter   ---   5
Counter   ---   4
Counter   ---   3
Counter   ---   2
Counter   ---   1
Thread Thread - 2  exiting.