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Diffstat (limited to 'appc-common/src/main/java/org/openecomp/appc/pool/CachedElement.java')
-rw-r--r-- | appc-common/src/main/java/org/openecomp/appc/pool/CachedElement.java | 208 |
1 files changed, 208 insertions, 0 deletions
diff --git a/appc-common/src/main/java/org/openecomp/appc/pool/CachedElement.java b/appc-common/src/main/java/org/openecomp/appc/pool/CachedElement.java new file mode 100644 index 000000000..558b2a33a --- /dev/null +++ b/appc-common/src/main/java/org/openecomp/appc/pool/CachedElement.java @@ -0,0 +1,208 @@ +/*- + * ============LICENSE_START======================================================= + * openECOMP : APP-C + * ================================================================================ + * Copyright (C) 2017 AT&T Intellectual Property. All rights + * reserved. + * ================================================================================ + * 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 + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + * ============LICENSE_END========================================================= + */ + + + +package org.openecomp.appc.pool; + +import java.io.Closeable; +import java.io.IOException; +import java.lang.reflect.InvocationHandler; +import java.lang.reflect.Method; +import java.lang.reflect.Proxy; +import java.util.concurrent.atomic.AtomicBoolean; + +/** + * This class is used as a "wrapper" for any closeable elements that are cached in a pool. It is implemented as a + * dynamic proxy, so that it appears to be the same class of object to the client as the interface being cached. The + * generic type being cached MUST be an interface. + * @param <T> + * The generic type that we create a cached element for. This type is used to wrap instances of this type and + * expose access to the {@link java.io.Closeable} interface by using a dynamic proxy. + */ + +public class CachedElement<T extends Closeable> implements Closeable, InvocationHandler, CacheManagement { + + /** + * The pool that is managing this cached element + */ + private Pool<T> pool; + + /** + * The element that we are caching in the pool + */ + private T element; + + /** + * A thread-safe atomic indicator that tells us that the wrapped element has been released to the pool already, and + * not to do it again. + */ + private AtomicBoolean released = new AtomicBoolean(false); + + /** + * Create a new instance of a cached element dynamic proxy for use in the pool. + * <p> + * This returns an instance of the proxy to the caller that appears to be the same interface(s) as the object being + * cached. The dynamic proxy then intercepts all open and close semantics and directs that element to the pool. + * </p> + * <p> + * If the object being proxied does not implement the {@link CacheManagement} interface, then that interface is + * added to the dynamic proxy being created. This interface is actually implemented by the invocation handler (this + * object) for the proxy and allows direct access to the wrapped object inside the proxy. + * </p> + * + * @param pool + * The pool that we are caching these elements within + * @param element + * The element actually being cached + * @param interfaces + * The interface list of interfaces the element must implement (usually one) + * @return The dynamic proxy + */ + @SuppressWarnings("unchecked") + public static <T extends Closeable> T newInstance(Pool<T> pool, T element, Class<?>[] interfaces) { + ClassLoader cl = element.getClass().getClassLoader(); + CachedElement<T> ce = new CachedElement<>(pool, element); + boolean found = false; + for (Class<?> intf : interfaces) { + if (intf.getName().equals(CacheManagement.class.getName())) { + found = true; + break; + } + } + + int length = found ? interfaces.length : interfaces.length + 1; + Class<?>[] proxyInterfaces = new Class[length]; + System.arraycopy(interfaces, 0, proxyInterfaces, 0, interfaces.length); + + if (!found) { + proxyInterfaces[interfaces.length] = CacheManagement.class; + } + + return (T) Proxy.newProxyInstance(cl, proxyInterfaces, ce); + } + + /** + * Construct a cached element and assign it to the pool as a free element + * + * @param pool + * The pool that the element will be managed within + * @param element + * The element we are caching + */ + @SuppressWarnings("unchecked") + public CachedElement(Pool<T> pool, T element) { + this.pool = pool; + this.element = element; + + try { + pool.release((T) this); + } catch (PoolDrainedException e) { + e.printStackTrace(); + } + } + + /** + * This method delegates the close call to the actual wrapped element. + * <p> + * NOTE: This is not the same method that is called by the dynamic proxy. This method is in place to satisfy the + * signature of the {@link java.io.Closeable} interface. If it were to be called directly, then we will delegate the + * close to the underlying context. However, when the cached element is called as a synamic proxy, entry is in the + * {@link #invoke(Object, Method, Object[])} method. + * </p> + * + * @see java.io.Closeable#close() + */ + @Override + public void close() throws IOException { + element.close(); + } + + /** + * This method is the magic part of dynamic proxies. When the caller makes a method call based on the interface + * being proxied, this method is given control. This informs us of the method and arguments of the call. The object + * reference is that of the dynamic proxy itself, which is us. + * <p> + * Here we will check to see if the user is trying to close the "element" (the dynamic proxy acts like the wrapped + * element). If he is, then we don't really close it, but instead release the element that we are wrapping back to + * the free pool. Once this has happened, we mark the element as "closed" (from the perspective of this dynamic + * proxy) so that we wont try to release it again. + * </p> + * <p> + * If the method is the <code>equals</code> method then we assume that we are comparing the cached element in one + * dynamic proxy to the cached element in another. We execute the comparison between the cached elements, and not + * the dynamic proxies themselves. This preserves the allusion to the caller that the dynamic proxy is the object + * being wrapped. + * </p> + * <p> + * For convenience, we also implement the <code>getWrappedObject</code> method so that the dynamic proxy can be + * called to obtain the actual wrapped object if desired. Note, to use this method, the caller would have to invoke + * it through reflection. + * </p> + * <p> + * If the method being invoked is not one that we intercept, then we simply delegate that method onto the wrapped + * object. + * </p> + * + * @see java.lang.reflect.InvocationHandler#invoke(java.lang.Object, java.lang.reflect.Method, java.lang.Object[]) + */ + @SuppressWarnings({ + "unchecked", "nls" + }) + @Override + public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { + Object result = null; + + if (method.getName().equals("close")) { + if (released.compareAndSet(false, true)) { + if (!pool.isDrained()) { + pool.release((T) proxy); + } + } + } else if (method.getName().equals("equals")) { + CacheManagement cm = (CacheManagement) proxy; + T other = (T) cm.getWrappedObject(); + result = element.equals(other); + } else if (method.getName().equals("getWrappedObject")) { + return element; + } else { + result = method.invoke(element, args); + } + + return result; + } + + /** + * This method is used to be able to access the wrapped object underneath the dynamic proxy + * + * @see org.openecomp.appc.pool.CacheManagement#getWrappedObject() + */ + @Override + public T getWrappedObject() { + return element; + } + + @SuppressWarnings("nls") + @Override + public String toString() { + return element == null ? "null" : element.toString(); + } +} |