com.torchmind.observable.concurrent.AbstractBlockingObservable Maven / Gradle / Ivy
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Provides simple observable properties with binding capabilities.
/*
* Copyright 2017 Johannes Donath
* and other copyright owners as documented in the project's IP log.
*
* 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.
*/
package com.torchmind.observable.concurrent;
import com.torchmind.observable.Observable;
import com.torchmind.observable.ReadOnlyObservable;
import com.torchmind.observable.listener.ChangeListener;
import com.torchmind.observable.listener.ValidationListener;
import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import javax.annotation.Nonnull;
import javax.annotation.Nullable;
/**
* Provides a blocking abstract implementation of the observable specification.
*
* @author Johannes Donath
*/
public abstract class AbstractBlockingObservable extends
AbstractConcurrentReadOnlyObservable implements Observable {
private final ReadWriteLock lock;
private final ValidationListener validationListener;
private final Set> bidirectionalBinding = new HashSet<>();
private V value;
private final ChangeListener bindingListener = (ChangeListener) (property, oldValue, newValue) -> {
// in case our invalidation flag is set, we have already received this update and probably
// discovered a circular reference between this observable and the caller and thus do not need
// to actually perform this update
if (!this.isValid()) {
return;
}
// otherwise we'll simply set the invalidation flag, update the value and call our subscribers
// before turning off the invalidation flag once again to complete the cycle
this.setInternal(newValue);
};
private ReadOnlyObservable binding;
public AbstractBlockingObservable(@Nullable ValidationListener validationListener, V value,
boolean fair) {
this.value = value;
this.validationListener = validationListener;
this.lock = new ReentrantReadWriteLock(fair);
}
public AbstractBlockingObservable(@Nullable ValidationListener validationListener, V value) {
this(validationListener, value, false);
}
public AbstractBlockingObservable(V value) {
this(null, value);
}
public AbstractBlockingObservable() {
this(null);
}
/**
* {@inheritDoc}
*/
@Override
public V get() {
this.lock.readLock().lock();
try {
return this.value;
} finally {
this.lock.readLock().unlock();
}
}
/**
* {@inheritDoc}
*/
@Override
public void set(V value) {
if (this.binding != null) {
throw new IllegalStateException(
"Cannot change observable: Value is bound to another observable");
}
this.setInternal(value);
}
/**
* Provides an internal setter for the purposes of skipping state sanity checks when necessary.
*/
private void setInternal(V value) {
this.lock.writeLock().lock();
try {
// even when we receive updates from a binding, we'll validate whether this value is valid
// Note, however, that this may cause unexpected behavior as the initial caller may not properly
// handle the exception
if (this.validationListener != null) {
this.validationListener.validate(this, value);
}
V oldValue = this.value;
this.value = value;
this.publishChange(oldValue, value);
} finally {
this.lock.writeLock().unlock();
}
}
/**
* {@inheritDoc}
*/
@Override
public boolean isValid() {
// generally we will consider the observable invalid as long as its write lock is actively being
// used by another thread (or possibly the same thread) as it will be lifted after the changes
// have been published - Note that this step makes this operation slightly more expensive than
// its non thread safe counterparts
if (this.lock.writeLock().tryLock()) {
this.lock.writeLock().unlock();
return true;
}
return false;
}
/**
* {@inheritDoc}
*/
@Override
public void bindTo(@Nonnull ReadOnlyObservable observable) {
this.lock.writeLock().lock();
try {
// if we are already bound to the passed observable we will simply ignore this call to avoid
// double testing (nor is an update necessary)
if (this.binding == observable) {
return;
}
if (this.binding != null || !this.bidirectionalBinding.isEmpty()) {
throw new IllegalStateException(
"Cannot bind to observable: Already in another binding relationship");
}
// register the binding locally (to ensure it stays loaded with weak registrations) and register
// our local change listener
this.binding = observable;
observable.registerListener(this.bindingListener);
// assume the value of the passed observable as part of the registration process to emulate the
// effects of changed values
this.setInternal(observable.get());
} finally {
this.lock.writeLock().unlock();
}
}
/**
* {@inheritDoc}
*/
@Override
public void bindBidirectionallyTo(@Nonnull Observable observable) {
this.lock.writeLock().lock();
try {
if (this.binding != null) {
throw new IllegalStateException(
"Cannot bind to observable: Already in another binding relationship");
}
// if we already have a binding relationship with the passed observable we will simply ignore
// this call as we are probably dealing with the recursive call initiated by this implementation
if (this.bidirectionalBinding.contains(observable)) {
return;
}
// register the binding locally (to ensure it stays loaded with weak registrations) and register
// our local change listener
this.bidirectionalBinding.add(observable);
observable.registerListener(this.bindingListener);
// assume the value of the passed observable as part of the registration process to emulate the
// effects of changed values if the binding was initiated by this observable
if (!observable.isBoundBidirectionallyTo(this)) {
this.setInternal(observable.get());
}
// instruct the other side to create the respective mirror of this relationship on their side
observable.bindBidirectionallyTo(this);
} finally {
this.lock.writeLock().unlock();
}
}
/**
* {@inheritDoc}
*/
@Override
public boolean isBound() {
this.lock.readLock().lock();
try {
return this.binding != null || !this.bidirectionalBinding.isEmpty();
} finally {
this.lock.readLock().unlock();
}
}
/**
* {@inheritDoc}
*/
@Override
public boolean isBoundTo(@Nonnull ReadOnlyObservable observable) {
this.lock.readLock().lock();
try {
return this.binding == observable;
} finally {
this.lock.readLock().unlock();
}
}
/**
* {@inheritDoc}
*/
@Override
public boolean isBoundBidirectionallyTo(@Nonnull Observable observable) {
this.lock.readLock().lock();
try {
return this.binding == null && this.bidirectionalBinding.contains(observable);
} finally {
this.lock.readLock().unlock();
}
}
/**
* {@inheritDoc}
*/
@Override
public boolean isBoundBidirectionally() {
this.lock.readLock().lock();
try {
return this.binding == null && !this.bidirectionalBinding.isEmpty();
} finally {
this.lock.readLock().unlock();
}
}
/**
* {@inheritDoc}
*/
@Override
public void unbind() {
this.lock.readLock().lock();
try {
if (this.binding == null) {
throw new IllegalStateException(
"Cannot unbind: No unidirectional binding relationship present");
}
this.binding.removeListener(this.bindingListener);
this.binding = null;
} finally {
this.lock.readLock().unlock();
}
}
/**
* {@inheritDoc}
*/
@Override
public void unbindAll() {
this.lock.writeLock().lock();
try {
if (this.binding == null && this.bidirectionalBinding.isEmpty()) {
throw new IllegalStateException("Cannot unbind: No binding relationships present");
}
// remove unidirectional bindings (if any) as a present binding implies that we aren't dealing
// with any bidirectional bindings either
if (this.binding != null) {
this.binding.removeListener(this.bindingListener);
this.binding = null;
} else {
new HashSet<>(this.bidirectionalBinding).forEach(this::unbindBidirectional);
}
} finally {
this.lock.writeLock().unlock();
}
}
/**
* {@inheritDoc}
*/
@Override
public void unbindBidirectional(@Nonnull Observable observable) {
this.lock.writeLock().lock();
try {
observable.removeListener(this.bindingListener);
this.bidirectionalBinding.remove(observable);
// remove the other side of the relationship if this relationship still exists (this check is
// performed to prevent infinite recursions and unexpected exceptions)
if (observable.isBoundBidirectionallyTo(this)) {
observable.unbindBidirectional(this);
}
} finally {
this.lock.writeLock().unlock();
}
}
}