com.google.gerrit.extensions.registration.DynamicItem Maven / Gradle / Ivy
// 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.gerrit.common.Nullable;
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.
*
* 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 {
/**
* Declare a singleton {@code DynamicItem} with a binder.
*
* Items must be defined in a Guice module before they can be bound:
*
*
* DynamicItem.itemOf(binder(), Interface.class);
* DynamicItem.bind(binder(), Interface.class).to(Impl.class);
*
*
* @param binder a new binder created in the module.
* @param member type of entry to store.
*/
public static void itemOf(Binder binder, Class member) {
itemOf(binder, TypeLiteral.get(member));
}
/**
* Declare a singleton {@code DynamicItem} with a binder.
*
* Items must be defined in a Guice module before they can be bound:
*
*
* DynamicSet.itemOf(binder(), new TypeLiteral<Thing<Foo>>() {});
*
*
* @param binder a new binder created in the module.
* @param member type of entry to store.
*/
public static void itemOf(Binder binder, TypeLiteral member) {
Key> key = keyFor(member);
binder.bind(key).toProvider(new DynamicItemProvider<>(member, key)).in(Scopes.SINGLETON);
}
/**
* Construct a single {@code DynamicItem} with a fixed value.
*
* Primarily useful for passing {@code DynamicItem}s to constructors in tests.
*
* @param member type of item.
* @param item item to store.
*/
public static DynamicItem itemOf(Class member, T item) {
return new DynamicItem<>(
keyFor(TypeLiteral.get(member)), Providers.of(item), PluginName.GERRIT);
}
@SuppressWarnings("unchecked")
private static Key> keyFor(TypeLiteral member) {
return (Key>)
Key.get(Types.newParameterizedType(DynamicItem.class, member.getType()));
}
/**
* 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 LinkedBindingBuilder bind(Binder binder, Class 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 LinkedBindingBuilder bind(Binder binder, TypeLiteral type) {
return binder.bind(type);
}
private final Key> key;
private final AtomicReference> ref;
DynamicItem(Key> key, Provider provider, String pluginName) {
Extension in = null;
if (provider != null) {
in = new Extension<>(pluginName, provider);
}
this.key = key;
this.ref = new AtomicReference<>(in);
}
@Nullable
public Extension getEntry() {
return ref.get();
}
/**
* 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.
*/
@Nullable
public T get() {
Extension item = ref.get();
return item != null ? item.get() : null;
}
/**
* Get the name of the plugin that has bound the configured item, or null.
*
* @return the name of the plugin that has bound the configured item; null if no implementation
* has been bound to the item. This is common if no plugin registered an implementation for
* the type.
*/
@Nullable
public String getPluginName() {
Extension item = ref.get();
return item != null ? item.getPluginName() : 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 impl, String pluginName) {
final Extension item = new Extension<>(pluginName, impl);
Extension old = null;
while (!ref.compareAndSet(old, item)) {
old = ref.get();
if (old != null && !PluginName.GERRIT.equals(old.getPluginName())) {
throw new ProvisionException(
String.format(
"%s already provided by %s, ignoring plugin %s",
key.getTypeLiteral(), old.getPluginName(), pluginName));
}
}
final Extension 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 set(Key key, Provider impl, String pluginName) {
final Extension item = new Extension<>(pluginName, impl);
Extension old = null;
while (!ref.compareAndSet(old, item)) {
old = ref.get();
if (old != null
&& !PluginName.GERRIT.equals(old.getPluginName())
&& !pluginName.equals(old.getPluginName())) {
// We allow to replace:
// 1. Gerrit core items, e.g. websession cache
// can be replaced by plugin implementation
// 2. Reload of current plugin
throw new ProvisionException(
String.format(
"%s already provided by %s, ignoring plugin %s",
this.key.getTypeLiteral(), old.getPluginName(), pluginName));
}
}
return new ReloadableHandle(key, item, old);
}
private class ReloadableHandle implements ReloadableRegistrationHandle {
private final Key handleKey;
private final Extension item;
private final Extension defaultItem;
ReloadableHandle(Key handleKey, Extension item, Extension defaultItem) {
this.handleKey = handleKey;
this.item = item;
this.defaultItem = defaultItem;
}
@Override
public Key getKey() {
return handleKey;
}
@Override
public void remove() {
ref.compareAndSet(item, defaultItem);
}
@Override
@Nullable
public ReloadableHandle replace(Key newKey, Provider newItem) {
Extension n = new Extension<>(item.getPluginName(), newItem);
if (ref.compareAndSet(item, n)) {
return new ReloadableHandle(newKey, n, defaultItem);
}
return null;
}
}
}