| /** |
| * |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you under the Apache License, Version 2.0 (the |
| * "License"); you may not use this file except in compliance |
| * with the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| package org.apache.hadoop.hbase.executor; |
| |
| import java.io.IOException; |
| import java.util.concurrent.atomic.AtomicLong; |
| |
| import org.apache.commons.logging.Log; |
| import org.apache.commons.logging.LogFactory; |
| import org.apache.hadoop.hbase.classification.InterfaceAudience; |
| import org.apache.hadoop.hbase.Server; |
| import org.apache.htrace.Span; |
| import org.apache.htrace.Trace; |
| import org.apache.htrace.TraceScope; |
| |
| /** |
| * Abstract base class for all HBase event handlers. Subclasses should |
| * implement the {@link #process()} and {@link #prepare()} methods. Subclasses |
| * should also do all necessary checks up in their prepare() if possible -- check |
| * table exists, is disabled, etc. -- so they fail fast rather than later when process |
| * is running. Do it this way because process be invoked directly but event |
| * handlers are also |
| * run in an executor context -- i.e. asynchronously -- and in this case, |
| * exceptions thrown at process time will not be seen by the invoker, not till |
| * we implement a call-back mechanism so the client can pick them up later. |
| * <p> |
| * Event handlers have an {@link EventType}. |
| * {@link EventType} is a list of ALL handler event types. We need to keep |
| * a full list in one place -- and as enums is a good shorthand for an |
| * implemenations -- because event handlers can be passed to executors when |
| * they are to be run asynchronously. The |
| * hbase executor, see ExecutorService, has a switch for passing |
| * event type to executor. |
| * <p> |
| * @see ExecutorService |
| */ |
| @InterfaceAudience.Private |
| public abstract class EventHandler implements Runnable, Comparable<Runnable> { |
| private static final Log LOG = LogFactory.getLog(EventHandler.class); |
| |
| // type of event this object represents |
| protected EventType eventType; |
| |
| protected Server server; |
| |
| // sequence id generator for default FIFO ordering of events |
| protected static final AtomicLong seqids = new AtomicLong(0); |
| |
| // sequence id for this event |
| private final long seqid; |
| |
| // Time to wait for events to happen, should be kept short |
| protected int waitingTimeForEvents; |
| |
| private final Span parent; |
| |
| /** |
| * Default base class constructor. |
| */ |
| public EventHandler(Server server, EventType eventType) { |
| this.parent = Trace.currentSpan(); |
| this.server = server; |
| this.eventType = eventType; |
| seqid = seqids.incrementAndGet(); |
| if (server != null) { |
| this.waitingTimeForEvents = server.getConfiguration(). |
| getInt("hbase.master.event.waiting.time", 1000); |
| } |
| } |
| |
| /** |
| * Event handlers should do all the necessary checks in this method (rather than |
| * in the constructor, or in process()) so that the caller, which is mostly executed |
| * in the ipc context can fail fast. Process is executed async from the client ipc, |
| * so this method gives a quick chance to do some basic checks. |
| * Should be called after constructing the EventHandler, and before process(). |
| * @return the instance of this class |
| * @throws Exception when something goes wrong |
| */ |
| public EventHandler prepare() throws Exception { |
| return this; |
| } |
| |
| @Override |
| public void run() { |
| TraceScope chunk = Trace.startSpan(this.getClass().getSimpleName(), parent); |
| try { |
| process(); |
| } catch(Throwable t) { |
| handleException(t); |
| } finally { |
| chunk.close(); |
| } |
| } |
| |
| /** |
| * This method is the main processing loop to be implemented by the various |
| * subclasses. |
| * @throws IOException |
| */ |
| public abstract void process() throws IOException; |
| |
| /** |
| * Return the event type |
| * @return The event type. |
| */ |
| public EventType getEventType() { |
| return this.eventType; |
| } |
| |
| /** |
| * Get the priority level for this handler instance. This uses natural |
| * ordering so lower numbers are higher priority. |
| * <p> |
| * Lowest priority is Integer.MAX_VALUE. Highest priority is 0. |
| * <p> |
| * Subclasses should override this method to allow prioritizing handlers. |
| * <p> |
| * Handlers with the same priority are handled in FIFO order. |
| * <p> |
| * @return Integer.MAX_VALUE by default, override to set higher priorities |
| */ |
| public int getPriority() { |
| return Integer.MAX_VALUE; |
| } |
| |
| /** |
| * @return This events' sequence id. |
| */ |
| public long getSeqid() { |
| return this.seqid; |
| } |
| |
| /** |
| * Default prioritized runnable comparator which implements a FIFO ordering. |
| * <p> |
| * Subclasses should not override this. Instead, if they want to implement |
| * priority beyond FIFO, they should override {@link #getPriority()}. |
| */ |
| @Override |
| public int compareTo(Runnable o) { |
| EventHandler eh = (EventHandler)o; |
| if(getPriority() != eh.getPriority()) { |
| return (getPriority() < eh.getPriority()) ? -1 : 1; |
| } |
| return (this.seqid < eh.seqid) ? -1 : 1; |
| } |
| |
| @Override |
| public String toString() { |
| return "Event #" + getSeqid() + |
| " of type " + eventType + |
| " (" + getInformativeName() + ")"; |
| } |
| |
| /** |
| * Event implementations should override thie class to provide an |
| * informative name about what event they are handling. For example, |
| * event-specific information such as which region or server is |
| * being processed should be included if possible. |
| */ |
| public String getInformativeName() { |
| return this.getClass().toString(); |
| } |
| |
| /** |
| * Event exception handler, may be overridden |
| * @param t Throwable object |
| */ |
| protected void handleException(Throwable t) { |
| String msg = "Caught throwable while processing event " + eventType; |
| LOG.error(msg, t); |
| if (server != null) { |
| server.abort(msg, t); |
| } |
| } |
| } |