Acquiring Locks in Mule Flows to avoid Racing Condition

Today, we're going to dive into some Java, using some code to acquire locks in your flow.

This can be useful when multiple threads of a single mule flow is trying to access a common shared resource (Lets say write to a file). We can aquire lock before accessing the shared resource and release the lock once the operation is done.

1. Create a LockSynchronizer.java file under src/main/java. This will initialize a semaphore    and its three functions lock() , unlock(), and getLock().

2. Below is the .java file under org.mule.util.locksynchronizer package.

package org.mule.util.locksynchronizer;

import java.util.concurrent.Semaphore;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

public class LockSynchronizer {
      private static final int MAX_PERMITS_NUMBER = 1;
      private static final Logger log = LogManager.getLogger(LockSynchronizer.class);

      private Semaphore semaphore;

      public void lock() {
            try {
                  getLock().acquire();
            } catch (InterruptedException e) {
                  log.error(e.getCause(), e);
            }
      }

      public void unlock() {
            getLock().release();
      }

      public Semaphore getLock() {
            if (semaphore == null) {
                  this.semaphore = new Semaphore(MAX_PERMITS_NUMBER);
            }
            return this.semaphore;
      }

}




3. Create a Spring Bean in the Mule XML file:

<spring:beans>
    <spring:bean id="LockSynchronizer" name="LockSynchronizer" class="org.mule.util.locksynchronizer" scope="singleton" />
</spring:beans>




4. Use the below expressions to acquire and release lock respectively:

• Acquire Lock:

<expression-component doc:name="Acquire lock"><![CDATA[app.registry['LockSynchronizer'].lock();]]>      </expression-component>




• Remove Lock:

<expression-component doc:name="Release lock"><![CDATA[app.registry['LockSynchronizer'].unlock();]]></expression-component>




• Get Lock Status:

<expression-component doc:name="Get lock status"><![CDATA[app.registry['LockSynchronizer'].getLock();]]></expression-component>

Thanks for reading!