    001    /*
    002     * Licensed to the Apache Software Foundation (ASF) under one or more
    003     * contributor license agreements.  See the NOTICE file distributed with
    004     * this work for additional information regarding copyright ownership.
    005     * The ASF licenses this file to You under the Apache License, Version 2.0
    006     * (the "License"); you may not use this file except in compliance with
    007     * the License.  You may obtain a copy of the License at
    008     *
    009     *     http://www.apache.org/licenses/LICENSE-2.0
    010     *
    011     * Unless required by applicable law or agreed to in writing, software
    012     * distributed under the License is distributed on an "AS IS" BASIS,
    013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014     * See the License for the specific language governing permissions and
    015     * limitations under the License.
    016     */
    017    package org.apache.commons.scxml.invoke;
    018
    019    import java.util.Map;
    020
    021    import org.apache.commons.scxml.SCInstance;
    022    import org.apache.commons.scxml.TriggerEvent;
    023
    024    /**
    025     * <p>The Invoker interface is used to define the possible interactions
    026     * between the parent state machine (executor) and the types of invocable
    027     * activities.</p>
    028     *
    029     * <p>Invocable activities must first register an Invoker implementation class
    030     * for the appropriate "targettype" (attribute of <invoke>) with the
    031     * parent <code>SCXMLExecutor</code>.</p>
    032     *
    033     * <p>The communication link between the parent state machine executor and
    034     * the invoked activity is a bi-directional events pipe.</p>
    035     *
    036     * <p>All events triggered on the parent state machine get forwarded to the
    037     * invoked activity. The processing semantics for these events depend
    038     * upon the "targettype", and thereby vary per concrete implementation of
    039     * this interface.</p>
    040     *
    041     * <p>The invoked activity in turn must fire a special "done" event
    042     * when it concludes. It may fire additional events before the "done"
    043     * event. The semantics of any additional events depend upon the
    044     * "targettype". The invoked activity must not fire any events after the
    045     * "done" event. The name of the special "done" event must be
    046     * the ID of the parent state wherein the corresponding <invoke>
    047     * resides, with the String ".invoke.done" appended.</p>
    048     *
    049     * <p>The Invoker "lifecycle" is outlined below:
    050     *  <ol>
    051     *   <li>Instantiation via {@link Class#newInstance()}
    052     *       (Invoker implementation requires accessible constructor).</li>
    053     *   <li>Configuration (setters for parent state ID and
    054     *       {@link SCInstance}).</li>
    055     *   <li>Initiation of invoked activity via invoke() method, passing
    056     *       the source URI and the map of params.</li>
    057     *   <li>Zero or more bi-directional event triggering.</li>
    058     *   <li>Either completion or cancellation.</li>
    059     *  </ol>
    060     * </p>
    061     *
    062     * <p><b>Note:</b> The semantics of <invoke> are necessarily
    063     * asynchronous, tending towards long(er) running interactions with external
    064     * processes. Implementations must not communicate with the parent state
    065     * machine executor in a synchronous manner. For synchronous
    066     * communication semantics, use <event> or custom actions instead.</p>
    067     */
    068    public interface Invoker {
    069
    070        /**
    071         * Set the state ID of the owning state for the <invoke>.
    072         * Implementations must use this ID for constructing the event name for
    073         * the special "done" event (and optionally, for other event names
    074         * as well).
    075         *
    076         * @param parentStateId The ID of the parent state.
    077         */
    078        void setParentStateId(String parentStateId);
    079
    080        /**
    081         * Set the "context" of the parent state machine, which provides the
    082         * channel.
    083         *
    084         * @param scInstance The "context" of the parent state machine.
    085         */
    086        void setSCInstance(SCInstance scInstance);
    087
    088        /**
    089         * Begin this invocation.
    090         *
    091         * @param source The source URI of the activity being invoked.
    092         * @param params The <param> values
    093         * @throws InvokerException In case there is a fatal problem with
    094         *                          invoking the source.
    095         */
    096        void invoke(String source, Map params)
    097        throws InvokerException;
    098
    099        /**
    100         * Forwards the events triggered on the parent state machine
    101         * on to the invoked activity.
    102         *
    103         * @param evts
    104         *            an array of external events which triggered during the last
    105         *            time quantum
    106         *
    107         * @throws InvokerException In case there is a fatal problem with
    108         *                          processing the events forwarded by the
    109         *                          parent state machine.
    110         */
    111        void parentEvents(TriggerEvent[] evts)
    112        throws InvokerException;
    113
    114        /**
    115         * Cancel this invocation.
    116         *
    117         * @throws InvokerException In case there is a fatal problem with
    118         *                          canceling this invoke.
    119         */
    120        void cancel()
    121        throws InvokerException;
    122
    123    }
    124