[Fix] Fixed race conditions in DefaultRuntimeRegistry, removed Regist…

…ry.exists(String, Class) method

the exists(String, Class) method could be misleading, as an IO with the given ID might exist, but has a different type. This would not make adding an IO with the given ID possible and would lead to exceptions later on.

pi4j-core/src/main/java/com/pi4j/registry/Registry.java

@@ -47,15 +47,6 @@
  * @version $Id: $Id
  */
 public interface Registry extends Describable {
-
-    /**
-     * <p>exists.</p>
-     *
-     * @param id a {@link java.lang.String} object.
-     * @param type a {@link java.lang.Class} object.
-     * @return a boolean.
-     */
-    boolean exists(String id, Class<? extends IO> type);
     /**
      * <p>exists.</p>
      *

pi4j-core/src/main/java/com/pi4j/registry/impl/DefaultRegistry.java

@@ -63,12 +63,6 @@ private DefaultRegistry(RuntimeRegistry registry) {
         this.registry = registry;
     }
 
-    /** {@inheritDoc} */
-    @Override
-    public boolean exists(String id, Class<? extends IO> type) {
-        return registry.exists(id, type);
-    }
-
     /** {@inheritDoc} */
     @Override
     public boolean exists(String id) {

pi4j-core/src/main/java/com/pi4j/registry/impl/DefaultRuntimeRegistry.java

@@ -10,7 +10,7 @@
  * This file is part of the Pi4J project. More information about
  * this project can be found here:  https://pi4j.com/
  * **********************************************************************
- * 
+ *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
@@ -45,9 +45,9 @@
  */
 public class DefaultRuntimeRegistry implements RuntimeRegistry {
 
-    private Logger logger = LoggerFactory.getLogger(this.getClass());
-    private Runtime runtime = null;
-    private Map<String, IO> instances = new ConcurrentHashMap<>();
+    private static final Logger logger = LoggerFactory.getLogger(DefaultRuntimeRegistry.class);
+    private final Runtime runtime;
+    private final Map<String, IO> instances;
 
     // static singleton instance
     /**
@@ -62,91 +62,76 @@ public static RuntimeRegistry newInstance(Runtime runtime){
 
     // private constructor
     private DefaultRuntimeRegistry(Runtime runtime) {
-        // forbid object construction
-
         // set local runtime reference
+        this.instances = new ConcurrentHashMap<>();
         this.runtime = runtime;
-    }
+	}
 
-    /** {@inheritDoc} */
     @Override
     public RuntimeRegistry add(IO instance) throws IOInvalidIDException, IOAlreadyExistsException {
-
         // validate target I/O instance id
         String _id = validateId(instance.id());
 
         // first test to make sure this id does not already exist in the registry
-        if(instances.containsKey(_id))
-            throw new IOAlreadyExistsException(_id);
+        synchronized (this.instances) {
+            if (instances.containsKey(_id))
+                throw new IOAlreadyExistsException(_id);
+
+            // add instance to collection
+            instances.put(_id, instance);
+        }
 
-        // add instance to collection
-        instances.put(_id, instance);
         return this;
     }
 
     /** {@inheritDoc} */
     @Override
     public <T extends IO> T get(String id, Class<T> type) throws IOInvalidIDException, IONotFoundException {
         String _id = validateId(id);
-
-        // first test to make sure this id is included in the registry
-        if(!instances.containsKey(_id))
+        T t = (T) instances.get(_id);
+        if(t == null)
             throw new IONotFoundException(_id);
-
-        return (T)instances.get(_id);
+        return t;
     }
 
     /** {@inheritDoc} */
     @Override
     public <T extends IO> T get(String id) throws IOInvalidIDException, IONotFoundException {
         String _id = validateId(id);
-
-        // first test to make sure this id is included in the registry
-        if(!instances.containsKey(_id))
+        T t = (T) instances.get(_id);
+        if(t == null)
             throw new IONotFoundException(_id);
-
-        return (T)instances.get(_id);
+        return t;
     }
 
     /** {@inheritDoc} */
     @Override
     public <T extends IO> T remove(String id) throws IONotFoundException, IOInvalidIDException, IOShutdownException {
-        String _id = validateId(id);
-        IO shutdownInstance = null;
-
-        // first test to make sure this id is included in the registry
-        if(!exists(_id))
-            throw new IONotFoundException(_id);
+        synchronized (this.instances) {
+            String _id = validateId(id);
 
-        // shutdown instance
-        try {
-            shutdownInstance = instances.get(_id);
-            shutdownInstance.shutdown(runtime.context());
-        }
-        catch (LifecycleException e){
-            logger.error(e.getMessage(), e);
-            throw new IOShutdownException(shutdownInstance, e);
-        }
+            // remove the instance from the registry
+            IO io = this.instances.remove(_id);
+            if (io == null)
+                throw new IONotFoundException(_id);
 
-        // remove the shutdown instance from the registry
-        this.instances.remove(_id);
+            // shutdown instance
+            try {
+                io.shutdown(runtime.context());
+            } catch (LifecycleException e) {
+                logger.error(e.getMessage(), e);
+                throw new IOShutdownException(io, e);
+            }
 
-        // return the shutdown I/O provider instances
-        return (T)shutdownInstance;
+            // return the shutdown I/O provider instances
+            return (T) io;
+        }
     }
 
     /** {@inheritDoc} */
     @Override
     public boolean exists(String id) {
-        String _id = null;
-        try {
-            _id = validateId(id);
-            // return 'false' if the requested ID is not found
-            // return 'true' if the requested ID is found
-            return instances.containsKey(_id);
-        } catch (IOInvalidIDException e) {
-            return false;
-        }
+        return instances.containsKey(validateId(id));
     }
 
     /** {@inheritDoc} */
@@ -155,28 +140,6 @@ public boolean exists(String id) {
         return Collections.unmodifiableMap(this.instances);
     }
 
-    /** {@inheritDoc} */
-    @Override
-    public boolean exists(String id, Class<? extends IO> type){
-        String _id = null;
-        try {
-            _id = validateId(id);
-
-            // return 'false' if the requested ID is not found
-            if(!instances.containsKey(_id))
-                return false;
-
-            // get the I/O instance
-            IO instance = instances.get(id);
-
-            // return true if the I/O instance matches the requested I/O type
-            return type.isAssignableFrom(instance.getClass());
-        } catch (IOInvalidIDException e) {
-            return false;
-        }
-    }
-
-
     private String validateId(String id) throws IOInvalidIDException {
         if(id == null)
              throw new IOInvalidIDException();
@@ -205,5 +168,4 @@ public RuntimeRegistry initialize() throws InitializeException {
         // NOTHING TO INITIALIZE
         return this;
     }
-
 }