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* Licensed to the Apache Software Foundation (ASF) under one
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* 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.regionserver;
import java.io.IOException;
import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.Map;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.Stoppable;
import org.apache.hadoop.hbase.log.HBaseMarkers;
import org.apache.hadoop.hbase.util.ShutdownHookManager;
import org.apache.hadoop.hbase.util.Threads;
import org.apache.yetus.audience.InterfaceAudience;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Manage regionserver shutdown hooks.
* @see #install(Configuration, FileSystem, Stoppable, Thread)
*/
@InterfaceAudience.Private
public class ShutdownHook {
private static final Logger LOG = LoggerFactory.getLogger(ShutdownHook.class);
private static final String CLIENT_FINALIZER_DATA_METHOD = "clientFinalizer";
/**
* Key for boolean configuration whose default is true.
*/
public static final String RUN_SHUTDOWN_HOOK = "hbase.shutdown.hook";
/**
* Key for a long configuration on how much time to wait on the fs shutdown hook. Default is 30
* seconds.
*/
public static final String FS_SHUTDOWN_HOOK_WAIT = "hbase.fs.shutdown.hook.wait";
/**
* A place for keeping track of all the filesystem shutdown hooks that need to be executed after
* the last regionserver referring to a given filesystem stops. We keep track of the # of
* regionserver references in values of the map.
*/
private final static Map fsShutdownHooks = new HashMap<>();
/**
* Install a shutdown hook that calls stop on the passed Stoppable and then thread joins against
* the passed threadToJoin. When this thread completes, it then runs the hdfs thread
* (This install removes the hdfs shutdown hook keeping a handle on it to run it after
* threadToJoin has stopped).
*
* To suppress all shutdown hook handling -- both the running of the regionserver hook and of the
* hdfs hook code -- set {@link ShutdownHook#RUN_SHUTDOWN_HOOK} in {@link Configuration} to
* false. This configuration value is checked when the hook code runs.
* @param fs Instance of Filesystem used by the RegionServer
* @param stop Installed shutdown hook will call stop against this passed
* Stoppable instance.
* @param threadToJoin After calling stop on stop will then join this thread.
*/
public static void install(final Configuration conf, final FileSystem fs, final Stoppable stop,
final Thread threadToJoin) {
Runnable fsShutdownHook = suppressHdfsShutdownHook(fs);
Thread t = new ShutdownHookThread(conf, stop, threadToJoin, fsShutdownHook);
ShutdownHookManager.affixShutdownHook(t, 0);
LOG.debug("Installed shutdown hook thread: " + t.getName());
}
/*
* Thread run by shutdown hook.
*/
private static class ShutdownHookThread extends Thread {
private final Stoppable stop;
private final Thread threadToJoin;
private final Runnable fsShutdownHook;
private final Configuration conf;
ShutdownHookThread(final Configuration conf, final Stoppable stop, final Thread threadToJoin,
final Runnable fsShutdownHook) {
super("Shutdownhook:" + threadToJoin.getName());
this.stop = stop;
this.threadToJoin = threadToJoin;
this.conf = conf;
this.fsShutdownHook = fsShutdownHook;
}
@Override
public void run() {
boolean b = this.conf.getBoolean(RUN_SHUTDOWN_HOOK, true);
LOG.info("Shutdown hook starting; " + RUN_SHUTDOWN_HOOK + "=" + b + "; fsShutdownHook="
+ this.fsShutdownHook);
if (b) {
this.stop.stop("Shutdown hook");
Threads.shutdown(this.threadToJoin);
if (this.fsShutdownHook != null) {
synchronized (fsShutdownHooks) {
int refs = fsShutdownHooks.get(fsShutdownHook);
if (refs == 1) {
LOG.info("Starting fs shutdown hook thread.");
Thread fsShutdownHookThread = (fsShutdownHook instanceof Thread)
? (Thread) fsShutdownHook
: new Thread(fsShutdownHook,
fsShutdownHook.getClass().getSimpleName() + "-shutdown-hook");
fsShutdownHookThread.start();
Threads.shutdown(fsShutdownHookThread,
this.conf.getLong(FS_SHUTDOWN_HOOK_WAIT, 30000));
}
if (refs > 0) {
fsShutdownHooks.put(fsShutdownHook, refs - 1);
}
}
}
}
LOG.info("Shutdown hook finished.");
}
}
/*
* So, HDFS keeps a static map of all FS instances. In order to make sure things are cleaned up on
* our way out, it also creates a shutdown hook so that all filesystems can be closed when the
* process is terminated; it calls FileSystem.closeAll. This inconveniently runs concurrently with
* our own shutdown handler, and therefore causes all the filesystems to be closed before the
* server can do all its necessary cleanup.
The dirty reflection in this method sneaks into the
* FileSystem class and grabs the shutdown hook, removes it from the list of active shutdown
* hooks, and returns the hook for the caller to run at its convenience.
This seems quite
* fragile and susceptible to breaking if Hadoop changes anything about the way this cleanup is
* managed. Keep an eye on things.
* @return The fs shutdown hook
* @throws RuntimeException if we fail to find or grap the shutdown hook.
*/
private static Runnable suppressHdfsShutdownHook(final FileSystem fs) {
try {
// This introspection has been updated to work for hadoop 0.20, 0.21 and for
// cloudera 0.20. 0.21 and cloudera 0.20 both have hadoop-4829. With the
// latter in place, things are a little messy in that there are now two
// instances of the data member clientFinalizer; an uninstalled one in
// FileSystem and one in the innner class named Cache that actually gets
// registered as a shutdown hook. If the latter is present, then we are
// on 0.21 or cloudera patched 0.20.
Runnable hdfsClientFinalizer = null;
// Look into the FileSystem#Cache class for clientFinalizer
Class[] classes = FileSystem.class.getDeclaredClasses();
Class cache = null;
for (Class c : classes) {
if (c.getSimpleName().equals("Cache")) {
cache = c;
break;
}
}
if (cache == null) {
throw new RuntimeException(
"This should not happen. Could not find the cache class in FileSystem.");
}
Field field = null;
try {
field = cache.getDeclaredField(CLIENT_FINALIZER_DATA_METHOD);
} catch (NoSuchFieldException e) {
// We can get here if the Cache class does not have a clientFinalizer
// instance: i.e. we're running on straight 0.20 w/o hadoop-4829.
}
if (field != null) {
field.setAccessible(true);
Field cacheField = FileSystem.class.getDeclaredField("CACHE");
cacheField.setAccessible(true);
Object cacheInstance = cacheField.get(fs);
hdfsClientFinalizer = (Runnable) field.get(cacheInstance);
} else {
// Then we didnt' find clientFinalizer in Cache. Presume clean 0.20 hadoop.
field = FileSystem.class.getDeclaredField(CLIENT_FINALIZER_DATA_METHOD);
field.setAccessible(true);
hdfsClientFinalizer = (Runnable) field.get(null);
}
if (hdfsClientFinalizer == null) {
throw new RuntimeException("Client finalizer is null, can't suppress!");
}
synchronized (fsShutdownHooks) {
boolean isFSCacheDisabled = fs.getConf().getBoolean("fs.hdfs.impl.disable.cache", false);
if (
!isFSCacheDisabled && !fsShutdownHooks.containsKey(hdfsClientFinalizer)
&& !ShutdownHookManager.deleteShutdownHook(hdfsClientFinalizer)
) {
throw new RuntimeException(
"Failed suppression of fs shutdown hook: " + hdfsClientFinalizer);
}
Integer refs = fsShutdownHooks.get(hdfsClientFinalizer);
fsShutdownHooks.put(hdfsClientFinalizer, refs == null ? 1 : refs + 1);
}
return hdfsClientFinalizer;
} catch (NoSuchFieldException nsfe) {
LOG.error(HBaseMarkers.FATAL, "Couldn't find field 'clientFinalizer' in FileSystem!", nsfe);
throw new RuntimeException("Failed to suppress HDFS shutdown hook");
} catch (IllegalAccessException iae) {
LOG.error(HBaseMarkers.FATAL, "Couldn't access field 'clientFinalizer' in FileSystem!", iae);
throw new RuntimeException("Failed to suppress HDFS shutdown hook");
}
}
// Thread that does nothing. Used in below main testing.
static class DoNothingThread extends Thread {
DoNothingThread() {
super("donothing");
}
@Override
public void run() {
super.run();
}
}
// Stoppable with nothing to stop. Used below in main testing.
static class DoNothingStoppable implements Stoppable {
@Override
public boolean isStopped() {
// TODO Auto-generated method stub
return false;
}
@Override
public void stop(String why) {
// TODO Auto-generated method stub
}
}
/**
* Main to test basic functionality. Run with clean hadoop 0.20 and hadoop 0.21 and cloudera
* patched hadoop to make sure our shutdown hook handling works for all compbinations. Pass
* '-Dhbase.shutdown.hook=false' to test turning off the running of shutdown hooks.
*/
public static void main(final String[] args) throws IOException {
Configuration conf = HBaseConfiguration.create();
String prop = System.getProperty(RUN_SHUTDOWN_HOOK);
if (prop != null) {
conf.setBoolean(RUN_SHUTDOWN_HOOK, Boolean.parseBoolean(prop));
}
// Instantiate a FileSystem. This will register the fs shutdown hook.
FileSystem fs = FileSystem.get(conf);
Thread donothing = new DoNothingThread();
donothing.start();
ShutdownHook.install(conf, fs, new DoNothingStoppable(), donothing);
}
}