001    // Copyright 2006, 2009, 2011 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    
015    package org.apache.tapestry5.ioc;
016    
017    
018    /**
019     * Similiar to {@link Runnable} execept 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     */
026    public interface Invokable<T>
027    {
028        /**
029         * Called to produce a value.
030         */
031        T invoke();
032    }