org.apache.nifi.components.ClassloaderIsolationKeyProvider Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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 org.apache.nifi.components;
import org.apache.nifi.context.PropertyContext;
/**
*
* There are times when a component must be created in such a way that each instance gets its own ClassLoader hierarchy,
* rather than sharing the ClassLoader with other components (see {@link org.apache.nifi.annotation.behavior.RequiresInstanceClassLoading @RequiresInstanceClassLoading}).
* This, however, can be extremely expensive, as all of the classes must be loaded again for each instance of the component. When thousands of these
* components are used in a single flow, the startup time can be great, and it can lead to massive amounts of RAM being required.
*
*
*
* For components that do require instance ClassLoading that clones ancestor resources, this interface can be optional implemented by the component.
* If the interface is implemented, the component is given the opportunity to return a distinct "key" that can be used to identify instances that may share
* the same ClassLoader.
*
*/
public interface ClassloaderIsolationKeyProvider {
/**
*
* Determines the key that identifies a shared ClassLoader that this component may use. Any two instances of the same component that return
* the same key may be assigned the same base ClassLoader (though it is not guaranteed that this will be the case).
*
*
*
* If a subsequent call to this method returns a different value, the component will be recreated with a different ClassLoader.
*
*
*
* Implementation Note: for components that implement this interface, this method will be called often. Therefore, performance characteristics
* of the implementation are critical. The method is expected to return the value of a configured property or derive a value to return based off
* of the values of a few properties. Accessing a remote resource, is too expensive. If the necessary computation is non-trivial, then it should be
* performed out of band and the pre-computed value simply returned by this method.
*
*
* @param context the PropertyContext that can be used for determining the key
* @return a distinct key that can be used to indicate which shared ClassLoader is allowed to be used
*/
String getClassloaderIsolationKey(PropertyContext context);
}