// Copyright (C) 2012 The Android Open Source Project
//
// 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.google.gerrit.extensions.registration;
import com.google.inject.Binder;
import com.google.inject.Key;
import com.google.inject.Provider;
import com.google.inject.ProvisionException;
import com.google.inject.Scopes;
import com.google.inject.TypeLiteral;
import com.google.inject.binder.LinkedBindingBuilder;
import com.google.inject.util.Providers;
import com.google.inject.util.Types;
import java.util.concurrent.atomic.AtomicReference;
/**
* A single item that can be modified as plugins reload.
* <p>
* DynamicItems are always mapped as singletons in Guice. Items store a Provider
* internally, and resolve the provider to an instance on demand. This enables
* registrations to decide between singleton and non-singleton members. If
* multiple plugins try to provide the same Provider, an exception is thrown.
*/
public class DynamicItem<T> {
/** Pair of provider implementation and plugin providing it. */
static class NamedProvider<T> {
final Provider<T> impl;
final String pluginName;
NamedProvider(Provider<T> provider, String pluginName) {
this.impl = provider;
this.pluginName = pluginName;
}
}
/**
* Declare a singleton {@code DynamicItem<T>} with a binder.
* <p>
* Items must be defined in a Guice module before they can be bound:
* <pre>
* DynamicItem.itemOf(binder(), Interface.class);
* DynamicItem.bind(binder(), Interface.class).to(Impl.class);
* </pre>
*
* @param binder a new binder created in the module.
* @param member type of entry to store.
*/
public static <T> void itemOf(Binder binder, Class<T> member) {
itemOf(binder, TypeLiteral.get(member));
}
/**
* Declare a singleton {@code DynamicItem<T>} with a binder.
* <p>
* Items must be defined in a Guice module before they can be bound:
* <pre>
* DynamicSet.itemOf(binder(), new TypeLiteral<Thing<Foo>>() {});
* </pre>
*
* @param binder a new binder created in the module.
* @param member type of entry to store.
*/
public static <T> void itemOf(Binder binder, TypeLiteral<T> member) {
@SuppressWarnings("unchecked")
Key<DynamicItem<T>> key = (Key<DynamicItem<T>>) Key.get(
Types.newParameterizedType(DynamicItem.class, member.getType()));
binder.bind(key)
.toProvider(new DynamicItemProvider<>(member, key))
.in(Scopes.SINGLETON);
}
/**
* Bind one implementation as the item using a unique annotation.
*
* @param binder a new binder created in the module.
* @param type type of entry to store.
* @return a binder to continue configuring the new item.
*/
public static <T> LinkedBindingBuilder<T> bind(Binder binder, Class<T> type) {
return bind(binder, TypeLiteral.get(type));
}
/**
* Bind one implementation as the item.
*
* @param binder a new binder created in the module.
* @param type type of entry to store.
* @return a binder to continue configuring the new item.
*/
public static <T> LinkedBindingBuilder<T> bind(Binder binder,
TypeLiteral<T> type) {
return binder.bind(type);
}
private final Key<DynamicItem<T>> key;
private final AtomicReference<NamedProvider<T>> ref;
DynamicItem(Key<DynamicItem<T>> key, Provider<T> provider, String pluginName) {
NamedProvider<T> in = null;
if (provider != null) {
in = new NamedProvider<>(provider, pluginName);
}
this.key = key;
this.ref = new AtomicReference<>(in);
}
/**
* Get the configured item, or null.
*
* @return the configured item instance; null if no implementation has been
* bound to the item. This is common if no plugin registered an
* implementation for the type.
*/
public T get() {
NamedProvider<T> item = ref.get();
return item != null ? item.impl.get() : null;
}
/**
* Set the element to provide.
*
* @param item the item to use. Must not be null.
* @param pluginName the name of the plugin providing the item.
* @return handle to remove the item at a later point in time.
*/
public RegistrationHandle set(T item, String pluginName) {
return set(Providers.of(item), pluginName);
}
/**
* Set the element to provide.
*
* @param impl the item to add to the collection. Must not be null.
* @param pluginName name of the source providing the implementation.
* @return handle to remove the item at a later point in time.
*/
public RegistrationHandle set(Provider<T> impl, String pluginName) {
final NamedProvider<T> item = new NamedProvider<>(impl, pluginName);
NamedProvider<T> old = null;
while (!ref.compareAndSet(old, item)) {
old = ref.get();
if (old != null && !"gerrit".equals(old.pluginName)) {
throw new ProvisionException(String.format(
"%s already provided by %s, ignoring plugin %s",
key.getTypeLiteral(), old.pluginName, pluginName));
}
}
final NamedProvider<T> defaultItem = old;
return new RegistrationHandle() {
@Override
public void remove() {
ref.compareAndSet(item, defaultItem);
}
};
}
/**
* Set the element that may be hot-replaceable in the future.
*
* @param key unique description from the item's Guice binding. This can be
* later obtained from the registration handle to facilitate matching
* with the new equivalent instance during a hot reload.
* @param impl the item to set as our value right now. Must not be null.
* @param pluginName the name of the plugin providing the item.
* @return a handle that can remove this item later, or hot-swap the item.
*/
public ReloadableRegistrationHandle<T> set(Key<T> key, Provider<T> impl,
String pluginName) {
final NamedProvider<T> item = new NamedProvider<>(impl, pluginName);
NamedProvider<T> old = null;
while (!ref.compareAndSet(old, item)) {
old = ref.get();
if (old != null && !"gerrit".equals(old.pluginName)) {
throw new ProvisionException(String.format(
"%s already provided by %s, ignoring plugin %s",
this.key.getTypeLiteral(), old.pluginName, pluginName));
}
}
return new ReloadableHandle(key, item, old);
}
private class ReloadableHandle implements ReloadableRegistrationHandle<T> {
private final Key<T> key;
private final NamedProvider<T> item;
private final NamedProvider<T> defaultItem;
ReloadableHandle(Key<T> key, NamedProvider<T> item, NamedProvider<T> defaultItem) {
this.key = key;
this.item = item;
this.defaultItem = defaultItem;
}
@Override
public Key<T> getKey() {
return key;
}
@Override
public void remove() {
ref.compareAndSet(item, defaultItem);
}
@Override
public ReloadableHandle replace(Key<T> newKey, Provider<T> newItem) {
NamedProvider<T> n = new NamedProvider<>(newItem, item.pluginName);
if (ref.compareAndSet(item, n)) {
return new ReloadableHandle(newKey, n, defaultItem);
}
return null;
}
}
}