001// Copyright 2006, 2009, 2011, 2013 The Apache Software Foundation
002//
003// Licensed under the Apache License, Version 2.0 (the "License");
004// you may not use this file except in compliance with the License.
005// You may obtain a copy of the License at
006//
007//     http://www.apache.org/licenses/LICENSE-2.0
008//
009// Unless required by applicable law or agreed to in writing, software
010// distributed under the License is distributed on an "AS IS" BASIS,
011// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012// See the License for the specific language governing permissions and
013// limitations under the License.
014
015package org.apache.tapestry5.ioc;
016
017
018/**
019 * Similar to {@link Runnable} except that it returns a value. Used to represent any operation which can return a
020 * value. This is often used in situations where the code is to be executed in another threads.
021 *
022 * @param <T> the return value type
023 * @see org.apache.tapestry5.ioc.OperationTracker#invoke(String, Invokable)
024 * @see org.apache.tapestry5.ioc.services.ParallelExecutor#invoke(Invokable)
025 * @see IOOperation
026 */
027public interface Invokable<T>
028{
029    /**
030     * Called to produce a value.
031     */
032    T invoke();
033}