| /******************************************************************************* |
| * Copyright (c) 2008, 2017 Matthew Hall and others. |
| * |
| * This program and the accompanying materials |
| * are made available under the terms of the Eclipse Public License 2.0 |
| * which accompanies this distribution, and is available at |
| * https://www.eclipse.org/legal/epl-2.0/ |
| * |
| * SPDX-License-Identifier: EPL-2.0 |
| * |
| * Contributors: |
| * Matthew Hall - initial API and implementation (bug 237703) |
| * Matthew Hall - bug 274081 |
| * Abel Hegedus - bug 414297 |
| * Stefan Xenos <sxenos@gmail.com> - Bug 335792 |
| *******************************************************************************/ |
| package org.eclipse.core.databinding.observable.set; |
| |
| import java.util.Collections; |
| import java.util.HashSet; |
| import java.util.Objects; |
| import java.util.Set; |
| import java.util.function.Supplier; |
| |
| import org.eclipse.core.databinding.observable.ChangeEvent; |
| import org.eclipse.core.databinding.observable.Diffs; |
| import org.eclipse.core.databinding.observable.IChangeListener; |
| import org.eclipse.core.databinding.observable.IObservable; |
| import org.eclipse.core.databinding.observable.IStaleListener; |
| import org.eclipse.core.databinding.observable.ObservableTracker; |
| import org.eclipse.core.databinding.observable.Realm; |
| import org.eclipse.core.databinding.observable.StaleEvent; |
| import org.eclipse.core.databinding.observable.value.IObservableValue; |
| |
| /** |
| * A lazily calculated set that automatically computes and registers listeners |
| * on its dependencies as long as all of its dependencies are |
| * {@link IObservable} objects. Any change to one of the observable dependencies |
| * causes the set to be recomputed. |
| * <p> |
| * This class is thread safe. All state accessing methods must be invoked from |
| * the {@link Realm#isCurrent() current realm}. Methods for adding and removing |
| * listeners may be invoked from any thread. |
| * </p> |
| * <p> |
| * Example: compute the set of all primes greater than 1 and less than the value |
| * of an {@link IObservableValue} < {@link Integer} >. |
| * </p> |
| * |
| * <pre> |
| * final IObservableValue max = WritableValue.withValueType(Integer.TYPE); |
| * max.setValue(Integer.valueOf(0)); |
| * IObservableSet primes = new ComputedSet() { |
| * protected Set calculate() { |
| * int maxVal = ((Integer) max.getValue()).intValue(); |
| * |
| * Set result = new HashSet(); |
| * outer: for (int i = 2; i < maxVal; i++) { |
| * for (Iterator it = result.iterator(); it.hasNext();) { |
| * Integer knownPrime = (Integer) it.next(); |
| * if (i % knownPrime.intValue() == 0) |
| * continue outer; |
| * } |
| * result.add(Integer.valueOf(i)); |
| * } |
| * return result; |
| * } |
| * }; |
| * |
| * System.out.println(primes); // => "[]" |
| * |
| * max.setValue(Integer.valueOf(20)); |
| * System.out.println(primes); // => "[2, 3, 5, 7, 11, 13, 17, 19]" |
| * </pre> |
| * |
| * @param <E> |
| * the type of the elements in this set |
| * |
| * @since 1.2 |
| */ |
| public abstract class ComputedSet<E> extends AbstractObservableSet<E> { |
| private Set<E> cachedSet = new HashSet<>(); |
| |
| private boolean dirty = true; |
| private boolean stale = false; |
| |
| private IObservable[] dependencies = new IObservable[0]; |
| |
| /** |
| * Factory method to create {@link ComputedSet} objects in an easy manner. |
| * <p> |
| * The created list has a null {@link IObservableSet#getElementType}. |
| * |
| * @param supplier {@link Supplier}, which is tracked using |
| * {@link ObservableTracker} to find out observables it uses, in |
| * the same manner as {@link #calculate}. |
| * @return {@link ComputedSet} whose elements are computed using the given |
| * {@link Supplier}. |
| * @since 1.12 |
| */ |
| public static <E> IObservableSet<E> create(Supplier<Set<E>> supplier) { |
| Objects.requireNonNull(supplier); |
| return new ComputedSet<E>() { |
| @Override |
| protected Set<E> calculate() { |
| return supplier.get(); |
| } |
| }; |
| } |
| |
| /** |
| * Creates a computed set in the default realm and with an unknown (null) |
| * element type. |
| */ |
| public ComputedSet() { |
| this(Realm.getDefault(), null); |
| } |
| |
| /** |
| * Creates a computed set in the default realm and with the given element |
| * type. |
| * |
| * @param elementType |
| * the element type, may be <code>null</code> to indicate unknown |
| * element type |
| */ |
| public ComputedSet(Object elementType) { |
| this(Realm.getDefault(), elementType); |
| } |
| |
| /** |
| * Creates a computed set in given realm and with an unknown (null) element |
| * type. |
| * |
| * @param realm |
| * the realm |
| * |
| */ |
| public ComputedSet(Realm realm) { |
| this(realm, null); |
| } |
| |
| /** |
| * Creates a computed set in the given realm and with the given element |
| * type. |
| * |
| * @param realm |
| * the realm |
| * @param elementType |
| * the element type, may be <code>null</code> to indicate unknown |
| * element type |
| */ |
| public ComputedSet(Realm realm, Object elementType) { |
| super(realm); |
| this.elementType = elementType; |
| } |
| |
| /** |
| * Inner class that implements interfaces that we don't want to expose as |
| * public API. Each interface could have been implemented using a separate |
| * anonymous class, but we combine them here to reduce the memory overhead |
| * and number of classes. |
| * |
| * <p> |
| * The Runnable calls calculate and stores the result in cachedSet. |
| * </p> |
| * |
| * <p> |
| * The IChangeListener stores each observable in the dependencies list. This |
| * is registered as the listener when calling ObservableTracker, to detect |
| * every observable that is used by computeValue. |
| * </p> |
| * |
| * <p> |
| * The IChangeListener is attached to every dependency. |
| * </p> |
| * |
| */ |
| private class PrivateInterface implements Runnable, IChangeListener, |
| IStaleListener { |
| @Override |
| public void run() { |
| cachedSet = calculate(); |
| if (cachedSet == null) |
| cachedSet = Collections.EMPTY_SET; |
| } |
| |
| @Override |
| public void handleStale(StaleEvent event) { |
| if (!dirty) |
| makeStale(); |
| } |
| |
| @Override |
| public void handleChange(ChangeEvent event) { |
| makeDirty(); |
| } |
| } |
| |
| private PrivateInterface privateInterface = new PrivateInterface(); |
| |
| private Object elementType; |
| |
| protected int doGetSize() { |
| return doGetSet().size(); |
| } |
| |
| private final Set<E> getSet() { |
| getterCalled(); |
| return doGetSet(); |
| } |
| |
| @Override |
| protected Set<E> getWrappedSet() { |
| return doGetSet(); |
| } |
| |
| final Set<E> doGetSet() { |
| if (dirty) { |
| // This line will do the following: |
| // - Run the calculate method |
| // - While doing so, add any observable that is touched to the |
| // dependencies list |
| IObservable[] newDependencies = ObservableTracker.runAndMonitor( |
| privateInterface, privateInterface, null); |
| |
| // If any dependencies are stale, a stale event will be fired here |
| // even if we were already stale before recomputing. This is in case |
| // clients assume that a set change is indicative of non-staleness. |
| stale = false; |
| for (IObservable newDependency : newDependencies) { |
| if (newDependency.isStale()) { |
| makeStale(); |
| break; |
| } |
| } |
| |
| if (!stale) { |
| for (IObservable newDependency : newDependencies) { |
| newDependency.addStaleListener(privateInterface); |
| } |
| } |
| |
| dependencies = newDependencies; |
| |
| dirty = false; |
| } |
| |
| return cachedSet; |
| } |
| |
| /** |
| * Subclasses must override this method to calculate the set contents. Any |
| * dependencies used to calculate the set must be {@link IObservable}, and |
| * implementers must use one of the interface methods tagged TrackedGetter |
| * for ComputedSet to recognize it as a dependency. |
| * |
| * @return the object's set. |
| */ |
| protected abstract Set<E> calculate(); |
| |
| private void makeDirty() { |
| if (!dirty) { |
| dirty = true; |
| |
| // copy the old set |
| // bug 414297: moved before makeStale(), as cachedSet may be |
| // overwritten |
| // in makeStale() if a listener calls isStale() |
| final Set<E> oldSet = new HashSet<>(cachedSet); |
| makeStale(); |
| |
| stopListening(); |
| |
| // Fire the "dirty" event. This implementation recomputes the new |
| // set lazily. |
| fireSetChange(new SetDiff<E>() { |
| SetDiff<E> delegate; |
| |
| private SetDiff<E> getDelegate() { |
| if (delegate == null) |
| delegate = Diffs.computeSetDiff(oldSet, getSet()); |
| return delegate; |
| } |
| |
| @Override |
| public Set<E> getAdditions() { |
| return getDelegate().getAdditions(); |
| } |
| |
| @Override |
| public Set<E> getRemovals() { |
| return getDelegate().getRemovals(); |
| } |
| }); |
| } |
| } |
| |
| private void stopListening() { |
| if (dependencies != null) { |
| for (IObservable observable : dependencies) { |
| observable.removeChangeListener(privateInterface); |
| observable.removeStaleListener(privateInterface); |
| } |
| dependencies = null; |
| } |
| } |
| |
| private void makeStale() { |
| if (!stale) { |
| stale = true; |
| fireStale(); |
| } |
| } |
| |
| @Override |
| public boolean isStale() { |
| // recalculate set if dirty, to ensure staleness is correct. |
| getSet(); |
| return stale; |
| } |
| |
| @Override |
| public Object getElementType() { |
| return elementType; |
| } |
| |
| @Override |
| public synchronized void addChangeListener(IChangeListener listener) { |
| super.addChangeListener(listener); |
| // If somebody is listening, we need to make sure we attach our own |
| // listeners |
| computeSetForListeners(); |
| } |
| |
| @Override |
| public synchronized void addSetChangeListener( |
| ISetChangeListener<? super E> listener) { |
| super.addSetChangeListener(listener); |
| // If somebody is listening, we need to make sure we attach our own |
| // listeners |
| computeSetForListeners(); |
| } |
| |
| private void computeSetForListeners() { |
| // Some clients just add a listener and expect to get notified even if |
| // they never called getValue(), so we have to call getValue() ourselves |
| // here to be sure. Need to be careful about realms though, this method |
| // can be called outside of our realm. |
| // See also bug 198211. If a client calls this outside of our realm, |
| // they may receive change notifications before the runnable below has |
| // been executed. It is their job to figure out what to do with those |
| // notifications. |
| getRealm().exec(() -> { |
| if (dependencies == null) { |
| // We are not currently listening. |
| // But someone is listening for changes. Call getValue() |
| // to make sure we start listening to the observables we |
| // depend on. |
| getSet(); |
| } |
| }); |
| } |
| |
| @Override |
| public synchronized void dispose() { |
| stopListening(); |
| super.dispose(); |
| } |
| } |