1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17
18 package org.apache.commons.pipeline.driver;
19
20 import java.util.ArrayList;
21 import java.util.List;
22 import org.apache.commons.pipeline.*;
23
24 /**
25 * This interface is used to define how processing for a stage is started,
26 * stopped, and run. AbstractStageDriver implementations may run stages in one or
27 * more threads, and use the {@link StageMonitor} interface to provide communication
28 * between the stage, the driver, and the enclosing pipeline.
29 */
30 public abstract class AbstractStageDriver implements StageDriver {
31
32 /**
33 * The stage to run.
34 */
35 protected Stage stage;
36
37 /**
38 * The context for the stage being run
39 */
40 protected StageContext context;
41
42 /**
43 * The current state of processing. In most drivers, this is used for
44 * thread control.
45 */
46 protected volatile State currentState = State.STOPPED;
47
48 /**
49 * Enumerated value indicating the fault tolerance level of the StageDriver.
50 */
51 protected FaultTolerance faultTolerance = FaultTolerance.NONE;
52
53 /**
54 * List of processing failures that have occurred.
55 */
56 protected List<ProcessingException> processingExceptions = new ArrayList<ProcessingException>();
57
58 /**
59 * List of errors that have occurred.
60 */
61 protected List<Throwable> errors = new ArrayList<Throwable>();
62
63 /**
64 * Creates a StageDriver for the specified stage.
65 *
66 * @param stage The stage for which the driver will be created
67 * @param context The context in which to run the stage
68 */
69 public AbstractStageDriver(Stage stage, StageContext context) {
70 this(stage, context, FaultTolerance.NONE);
71 }
72
73 /**
74 * Creates a StageDriver for the specified stage.
75 *
76 * @param stage The stage for which the driver will be created
77 * @param context The context in which to run the stage
78 */
79 public AbstractStageDriver(Stage stage, StageContext context, FaultTolerance faultTolerance) {
80 if (stage == null) throw new IllegalArgumentException("Stage may not be null.");
81 if (context == null) throw new IllegalArgumentException("Context may not be null.");
82 this.stage = stage;
83 this.context = context;
84 this.faultTolerance = faultTolerance;
85 }
86
87 /**
88 * Returns the Stage being run by this StageDriver.
89 *
90 * @return The stage being run by this StageDriver instance
91 */
92 public Stage getStage() {
93 return this.stage;
94 }
95
96 /**
97 * This method is used to provide a communication channel between the context
98 * in which the driver is being run and the managed stage.
99 * @return the Feeder used to feed objects to the managed stage for processing.
100 */
101 public abstract Feeder getFeeder();
102
103 /**
104 * Return the current state of stage processing.
105 * @return the current state of processing
106 */
107 public State getState() {
108 return this.currentState;
109 }
110
111 /**
112 * Atomically tests to determine whether or not the driver is in the one of
113 * the specified states.
114 */
115 protected synchronized boolean isInState(State... states) {
116 for (State state : states) if (state == currentState) return true;
117 return false;
118 }
119
120 /**
121 * Set the current state of stage processing and notify any listeners
122 * that may be waiting on a state change.
123 */
124 protected synchronized void setState(State nextState) {
125 this.currentState = nextState;
126 this.notifyAll();
127 }
128
129 /**
130 * This method performs an atomic conditional state transition change
131 * to the value specified by the nextState parameter if and only if the
132 * current state is equal to the test state.
133 */
134 protected synchronized boolean testAndSetState(State testState, State nextState) {
135 if (currentState == testState) {
136 setState(nextState);
137 return true;
138 } else {
139 return false;
140 }
141 }
142
143 /**
144 * This method is used to start the driver, run the
145 * {@link Stage#preprocess() preprocess()} method of the attached stage
146 * and to then begin processing any objects fed to this driver's Feeder.
147 *
148 * @throws org.apache.commons.pipeline.StageException Thrown if there is an error during stage startup. In most cases, such errors
149 * will be handled internally by the driver.
150 */
151 public abstract void start() throws StageException;
152
153 /**
154 * This method waits for the stage(s) queue(s) to empty and any processor thread(s) to exit
155 * cleanly and then calls release() to release any resources acquired during processing, if possible.
156 * @throws org.apache.commons.pipeline.StageException Thrown if there is an error during driver shutdown. Ordinarily such
157 * exceptions will be handled internally.
158 */
159 public abstract void finish() throws StageException;
160
161 /**
162 * Sets the failure tolerance flag for the worker thread. If faultTolerance
163 * is set to CHECKED, {@link StageException StageException}s thrown by
164 * the {@link Stage#process(Object)} method will not interrupt queue
165 * processing, but will simply be logged with a severity of ERROR.
166 * If faultTolerance is set to ALL, runtime exceptions will also be
167 * logged and otherwise ignored.
168 * @param faultTolerance the flag value
169 */
170 public final void setFaultTolerance(FaultTolerance faultTolerance) {
171 this.faultTolerance = faultTolerance;
172 }
173
174 /**
175 * Getter for property faultTolerant.
176 * @return Value of property faultTolerant.
177 */
178 public final FaultTolerance getFaultTolerance() {
179 return this.faultTolerance;
180 }
181
182 /**
183 * Store a fatal error.
184 * @param error The error to be stored for later analysis
185 */
186 protected void recordFatalError(Throwable error) {
187 this.errors.add(error);
188 }
189
190 /**
191 * Returns a list of unrecoverable errors that occurred during stage
192 * processing.
193 * @return A list of unrecoverable errors that occurred during stage processing.
194 */
195 public List<Throwable> getFatalErrors() {
196 return this.errors;
197 }
198
199 /**
200 * Store processing failure information for the specified data object.
201 * @param data The data being processed at the time of the error
202 * @param error The error encountered
203 */
204 protected void recordProcessingException(Object data, Throwable error) {
205 ProcessingException ex = new ProcessingException(this.stage, error, data, this.getState());
206 this.processingExceptions.add(ex);
207 }
208
209 /**
210 * Returns a list of errors that occurred while processing data objects,
211 * along with the objects that were being processed when the errors
212 * were generated.
213 * @return The list of non-fatal processing errors.
214 */
215 public List<ProcessingException> getProcessingExceptions() {
216 return this.processingExceptions;
217 }
218 }