Time for action – allocating an object with JNI

Let's define a background Watcher that will use an object shared between Java and C/C++ as a lock:

1. In Store.java, add two new methods to start and stop a watcher thread. These methods respectively return and take a long as parameter. This value helps us hold a native pointer on the Java side:

   public class Store implements StoreListener {
       ...
       public native long startWatcher();
       public native void stopWatcher(long pPointer);
   }

2. Create a new file, StoreThreadSafe.java. The StoreThreadSafe class inherits from the Store class and aims at making the Store instances thread-safe using synchronized Java blocks. Declare a static member field LOCK of type Object and define a default constructor:

   package com.packtpub.store;
   
   import com.packtpub.exception.InvalidTypeException;
   import com.packtpub.exception.NotExistingKeyException;
   
   public class StoreThreadSafe extends Store {
       protected static Object LOCK;
       
       public StoreThreadSafe(StoreListener...