1 /**
2 *
3 * Licensed to the Apache Software Foundation (ASF) under one
4 * or more contributor license agreements. See the NOTICE file
5 * distributed with this work for additional information
6 * regarding copyright ownership. The ASF licenses this file
7 * to you under the Apache License, Version 2.0 (the
8 * "License"); you may not use this file except in compliance
9 * with the License. You may obtain a copy of the License at
10 *
11 * http://www.apache.org/licenses/LICENSE-2.0
12 *
13 * Unless required by applicable law or agreed to in writing, software
14 * distributed under the License is distributed on an "AS IS" BASIS,
15 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16 * See the License for the specific language governing permissions and
17 * limitations under the License.
18 */
19 package org.apache.hadoop.hbase.executor;
20
21 import java.io.IOException;
22 import java.util.concurrent.atomic.AtomicLong;
23
24 import org.apache.commons.logging.Log;
25 import org.apache.commons.logging.LogFactory;
26 import org.apache.hadoop.classification.InterfaceAudience;
27 import org.apache.hadoop.hbase.Server;
28 import org.cloudera.htrace.Sampler;
29 import org.cloudera.htrace.Span;
30 import org.cloudera.htrace.Trace;
31 import org.cloudera.htrace.TraceScope;
32 import org.cloudera.htrace.impl.AlwaysSampler;
33
34
35 /**
36 * Abstract base class for all HBase event handlers. Subclasses should
37 * implement the {@link #process()} and {@link #prepare()} methods. Subclasses
38 * should also do all necessary checks up in their prepare() if possible -- check
39 * table exists, is disabled, etc. -- so they fail fast rather than later when process
40 * is running. Do it this way because process be invoked directly but event
41 * handlers are also
42 * run in an executor context -- i.e. asynchronously -- and in this case,
43 * exceptions thrown at process time will not be seen by the invoker, not till
44 * we implement a call-back mechanism so the client can pick them up later.
45 * <p>
46 * Event handlers have an {@link EventType}.
47 * {@link EventType} is a list of ALL handler event types. We need to keep
48 * a full list in one place -- and as enums is a good shorthand for an
49 * implemenations -- because event handlers can be passed to executors when
50 * they are to be run asynchronously. The
51 * hbase executor, see ExecutorService, has a switch for passing
52 * event type to executor.
53 * <p>
54 * Event listeners can be installed and will be called pre- and post- process if
55 * this EventHandler is run in a Thread (its a Runnable so if its {@link #run()}
56 * method gets called). Implement
57 * {@link EventHandlerListener}s, and registering using
58 * {@link #setListener(EventHandlerListener)}.
59 * @see ExecutorService
60 */
61 @InterfaceAudience.Private
62 public abstract class EventHandler implements Runnable, Comparable<Runnable> {
63 private static final Log LOG = LogFactory.getLog(EventHandler.class);
64
65 // type of event this object represents
66 protected EventType eventType;
67
68 protected Server server;
69
70 // sequence id generator for default FIFO ordering of events
71 protected static final AtomicLong seqids = new AtomicLong(0);
72
73 // sequence id for this event
74 private final long seqid;
75
76 // Listener to call pre- and post- processing. May be null.
77 private EventHandlerListener listener;
78
79 // Time to wait for events to happen, should be kept short
80 protected int waitingTimeForEvents;
81
82 private final Span parent;
83
84 /**
85 * This interface provides pre- and post-process hooks for events.
86 */
87 public interface EventHandlerListener {
88 /**
89 * Called before any event is processed
90 * @param event The event handler whose process method is about to be called.
91 */
92 void beforeProcess(EventHandler event);
93 /**
94 * Called after any event is processed
95 * @param event The event handler whose process method is about to be called.
96 */
97 void afterProcess(EventHandler event);
98 }
99
100 /**
101 * Default base class constructor.
102 */
103 public EventHandler(Server server, EventType eventType) {
104 this.parent = Trace.currentSpan();
105 this.server = server;
106 this.eventType = eventType;
107 seqid = seqids.incrementAndGet();
108 if (server != null) {
109 this.waitingTimeForEvents = server.getConfiguration().
110 getInt("hbase.master.event.waiting.time", 1000);
111 }
112 }
113
114 /**
115 * Event handlers should do all the necessary checks in this method (rather than
116 * in the constructor, or in process()) so that the caller, which is mostly executed
117 * in the ipc context can fail fast. Process is executed async from the client ipc,
118 * so this method gives a quick chance to do some basic checks.
119 * Should be called after constructing the EventHandler, and before process().
120 * @return the instance of this class
121 * @throws Exception when something goes wrong
122 */
123 public EventHandler prepare() throws Exception {
124 return this;
125 }
126
127 public void run() {
128 TraceScope chunk = Trace.startSpan(this.getClass().getSimpleName(), parent);
129 try {
130 if (getListener() != null) getListener().beforeProcess(this);
131 process();
132 if (getListener() != null) getListener().afterProcess(this);
133 } catch(Throwable t) {
134 LOG.error("Caught throwable while processing event " + eventType, t);
135 } finally {
136 chunk.close();
137 }
138 }
139
140 /**
141 * This method is the main processing loop to be implemented by the various
142 * subclasses.
143 * @throws IOException
144 */
145 public abstract void process() throws IOException;
146
147 /**
148 * Return the event type
149 * @return The event type.
150 */
151 public EventType getEventType() {
152 return this.eventType;
153 }
154
155 /**
156 * Get the priority level for this handler instance. This uses natural
157 * ordering so lower numbers are higher priority.
158 * <p>
159 * Lowest priority is Integer.MAX_VALUE. Highest priority is 0.
160 * <p>
161 * Subclasses should override this method to allow prioritizing handlers.
162 * <p>
163 * Handlers with the same priority are handled in FIFO order.
164 * <p>
165 * @return Integer.MAX_VALUE by default, override to set higher priorities
166 */
167 public int getPriority() {
168 return Integer.MAX_VALUE;
169 }
170
171 /**
172 * @return This events' sequence id.
173 */
174 public long getSeqid() {
175 return this.seqid;
176 }
177
178 /**
179 * Default prioritized runnable comparator which implements a FIFO ordering.
180 * <p>
181 * Subclasses should not override this. Instead, if they want to implement
182 * priority beyond FIFO, they should override {@link #getPriority()}.
183 */
184 @Override
185 public int compareTo(Runnable o) {
186 EventHandler eh = (EventHandler)o;
187 if(getPriority() != eh.getPriority()) {
188 return (getPriority() < eh.getPriority()) ? -1 : 1;
189 }
190 return (this.seqid < eh.seqid) ? -1 : 1;
191 }
192
193 /**
194 * @return Current listener or null if none set.
195 */
196 public synchronized EventHandlerListener getListener() {
197 return listener;
198 }
199
200 /**
201 * @param listener Listener to call pre- and post- {@link #process()}.
202 */
203 public synchronized void setListener(EventHandlerListener listener) {
204 this.listener = listener;
205 }
206
207 @Override
208 public String toString() {
209 return "Event #" + getSeqid() +
210 " of type " + eventType +
211 " (" + getInformativeName() + ")";
212 }
213
214 /**
215 * Event implementations should override thie class to provide an
216 * informative name about what event they are handling. For example,
217 * event-specific information such as which region or server is
218 * being processed should be included if possible.
219 */
220 public String getInformativeName() {
221 return this.getClass().toString();
222 }
223 }