| /******************************************************************************* |
| * Copyright (c) 2015, 2016 Google, Inc and others. |
| * All rights reserved. This program and the accompanying materials |
| * are made available under the terms of the Eclipse Public License v1.0 |
| * which accompanies this distribution, and is available at |
| * http://www.eclipse.org/legal/epl-v10.html |
| * |
| * Contributors: |
| * Stefan Xenos (Google) - Initial implementation |
| *******************************************************************************/ |
| package org.eclipse.jdt.internal.core.nd; |
| |
| import java.util.function.Supplier; |
| |
| /** |
| * Holds a reference to a database entity that may be retained across read locks. In normal circumstances, it |
| * is unsafe to retain a database address after a read lock is released since the object pointed to at that |
| * address may have been deleted in the meantime. This class addresses this problem by remembering both the |
| * address itself and enough information to determine whether that address is invalid and search for an |
| * equivalent object if the original is lost. |
| */ |
| public class DatabaseRef<T extends NdNode> implements Supplier<T> { |
| private final Nd nd; |
| private T lastResult; |
| private long writeCounter; |
| private final Supplier<T> searchFunction; |
| |
| /** |
| * Constructs a new {@link DatabaseRef} that will search for its target using the given search function. |
| */ |
| public DatabaseRef(Nd nd, Supplier<T> searchFunction) { |
| this.nd = nd; |
| this.searchFunction = searchFunction; |
| this.writeCounter = -1; |
| } |
| |
| /** |
| * Constructs a new {@link DatabaseRef} that will search for its target using the given search function. |
| */ |
| public DatabaseRef(Nd nd, Supplier<T> searchFunction, T initialResult) { |
| this.nd = nd; |
| this.searchFunction = searchFunction; |
| this.lastResult = initialResult; |
| this.writeCounter = this.nd.getWriteNumber(); |
| } |
| |
| /** |
| * Returns the referenced object or null if the object is no longer present in the database. |
| */ |
| public T get() { |
| long ndWriteNumber = this.nd.getWriteNumber(); |
| if (this.writeCounter == ndWriteNumber) { |
| return this.lastResult; |
| } |
| |
| T result = this.searchFunction.get(); |
| this.writeCounter = ndWriteNumber; |
| this.lastResult = result; |
| return result; |
| } |
| |
| public Nd getNd() { |
| return this.nd; |
| } |
| |
| /** |
| * Acquires a read lock. Callers must invoke close() on the result when done. |
| */ |
| public IReader lock() { |
| return this.nd.acquireReadLock(); |
| } |
| } |