gerrit-extension-api/src/main/java/com/google/gerrit/extensions/registration/DynamicItem.java - gerrit - Git at Google

 // 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&lt;Thing&lt;Foo&gt;&gt;() {});
    * </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) {
     Key<DynamicItem<T>> key = keyFor(member);
     binder.bind(key).toProvider(new DynamicItemProvider<>(member, key)).in(Scopes.SINGLETON);
   }

   /**
    * Construct a single {@code DynamicItem<T>} with a fixed value.
    *
    * <p>Primarily useful for passing {@code DynamicItem}s to constructors in tests.
    *
    * @param member type of item.
    * @param item item to store.
    */
   public static <T> DynamicItem<T> itemOf(Class<T> member, T item) {
     return new DynamicItem<>(keyFor(TypeLiteral.get(member)), Providers.of(item), "gerrit");
   }

   @SuppressWarnings("unchecked")
   private static <T> Key<DynamicItem<T>> keyFor(TypeLiteral<T> member) {
     return (Key<DynamicItem<T>>)
         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 <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) && !pluginName.equals(old.pluginName)) {
         // 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.pluginName, pluginName));
       }
     }
     return new ReloadableHandle(key, item, old);
   }

   private class ReloadableHandle implements ReloadableRegistrationHandle<T> {
     private final Key<T> handleKey;
     private final NamedProvider<T> item;
     private final NamedProvider<T> defaultItem;

     ReloadableHandle(Key<T> handleKey, NamedProvider<T> item, NamedProvider<T> defaultItem) {
       this.handleKey = handleKey;
       this.item = item;
       this.defaultItem = defaultItem;
     }

     @Override
     public Key<T> getKey() {
       return handleKey;
     }

     @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;
     }
   }
 }
	// 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) {
	Key<DynamicItem<T>> key = keyFor(member);
	binder.bind(key).toProvider(new DynamicItemProvider<>(member, key)).in(Scopes.SINGLETON);
	}

	/**
	* Construct a single {@code DynamicItem<T>} with a fixed value.
	*
	* <p>Primarily useful for passing {@code DynamicItem}s to constructors in tests.
	*
	* @param member type of item.
	* @param item item to store.
	*/
	public static <T> DynamicItem<T> itemOf(Class<T> member, T item) {
	return new DynamicItem<>(keyFor(TypeLiteral.get(member)), Providers.of(item), "gerrit");
	}

	@SuppressWarnings("unchecked")
	private static <T> Key<DynamicItem<T>> keyFor(TypeLiteral<T> member) {
	return (Key<DynamicItem<T>>)
	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 <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) && !pluginName.equals(old.pluginName)) {
	// 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.pluginName, pluginName));
	}
	}
	return new ReloadableHandle(key, item, old);
	}

	private class ReloadableHandle implements ReloadableRegistrationHandle<T> {
	private final Key<T> handleKey;
	private final NamedProvider<T> item;
	private final NamedProvider<T> defaultItem;

	ReloadableHandle(Key<T> handleKey, NamedProvider<T> item, NamedProvider<T> defaultItem) {
	this.handleKey = handleKey;
	this.item = item;
	this.defaultItem = defaultItem;
	}

	@Override
	public Key<T> getKey() {
	return handleKey;
	}

	@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;
	}
	}
	}