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