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/**
* 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.hdfs.server.namenode;
import java.io.IOException;
import java.net.URI;
import java.util.ArrayDeque;
import java.util.Deque;
import java.util.List;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.Semaphore;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.ipc.Server;
import org.apache.hadoop.util.ExitUtil;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Preconditions;
class FSEditLogAsync extends FSEditLog implements Runnable {
static final Logger LOG = LoggerFactory.getLogger(FSEditLog.class);
// use separate mutex to avoid possible deadlock when stopping the thread.
private final Object syncThreadLock = new Object();
private Thread syncThread;
private static final ThreadLocal THREAD_EDIT = new ThreadLocal();
// requires concurrent access from caller threads and syncing thread.
private final BlockingQueue editPendingQ =
new ArrayBlockingQueue(4096);
// only accessed by syncing thread so no synchronization required.
// queue is unbounded because it's effectively limited by the size
// of the edit log buffer - ie. a sync will eventually be forced.
private final Deque syncWaitQ = new ArrayDeque();
FSEditLogAsync(Configuration conf, NNStorage storage, List editsDirs) {
super(conf, storage, editsDirs);
// op instances cannot be shared due to queuing for background thread.
cache.disableCache();
}
private boolean isSyncThreadAlive() {
synchronized(syncThreadLock) {
return syncThread != null && syncThread.isAlive();
}
}
private void startSyncThread() {
synchronized(syncThreadLock) {
if (!isSyncThreadAlive()) {
syncThread = new Thread(this, this.getClass().getSimpleName());
syncThread.start();
}
}
}
private void stopSyncThread() {
synchronized(syncThreadLock) {
if (syncThread != null) {
try {
syncThread.interrupt();
syncThread.join();
} catch (InterruptedException e) {
// we're quitting anyway.
} finally {
syncThread = null;
}
}
}
}
@VisibleForTesting
@Override
public void restart() {
stopSyncThread();
startSyncThread();
}
@Override
void openForWrite(int layoutVersion) throws IOException {
try {
startSyncThread();
super.openForWrite(layoutVersion);
} catch (IOException ioe) {
stopSyncThread();
throw ioe;
}
}
@Override
public void close() {
super.close();
stopSyncThread();
}
@Override
void logEdit(final FSEditLogOp op) {
Edit edit = getEditInstance(op);
THREAD_EDIT.set(edit);
enqueueEdit(edit);
}
@Override
public void logSync() {
Edit edit = THREAD_EDIT.get();
if (edit != null) {
// do NOT remove to avoid expunge & rehash penalties.
THREAD_EDIT.set(null);
if (LOG.isDebugEnabled()) {
LOG.debug("logSync " + edit);
}
edit.logSyncWait();
}
}
@Override
public void logSyncAll() {
// doesn't actually log anything, just ensures that the queues are
// drained when it returns.
Edit edit = new SyncEdit(this, null){
@Override
public boolean logEdit() {
return true;
}
};
enqueueEdit(edit);
edit.logSyncWait();
}
// draining permits is intended to provide a high priority reservation.
// however, release of outstanding permits must be postponed until
// drained permits are restored to avoid starvation. logic has some races
// but is good enough to serve its purpose.
private Semaphore overflowMutex = new Semaphore(8){
private AtomicBoolean draining = new AtomicBoolean();
private AtomicInteger pendingReleases = new AtomicInteger();
@Override
public int drainPermits() {
draining.set(true);
return super.drainPermits();
}
// while draining, count the releases until release(int)
private void tryRelease(int permits) {
pendingReleases.getAndAdd(permits);
if (!draining.get()) {
super.release(pendingReleases.getAndSet(0));
}
}
@Override
public void release() {
tryRelease(1);
}
@Override
public void release(int permits) {
draining.set(false);
tryRelease(permits);
}
};
private void enqueueEdit(Edit edit) {
if (LOG.isDebugEnabled()) {
LOG.debug("logEdit " + edit);
}
try {
// not checking for overflow yet to avoid penalizing performance of
// the common case. if there is persistent overflow, a mutex will be
// use to throttle contention on the queue.
if (!editPendingQ.offer(edit)) {
Preconditions.checkState(
isSyncThreadAlive(), "sync thread is not alive");
if (Thread.holdsLock(this)) {
// if queue is full, synchronized caller must immediately relinquish
// the monitor before re-offering to avoid deadlock with sync thread
// which needs the monitor to write transactions.
int permits = overflowMutex.drainPermits();
try {
do {
this.wait(1000); // will be notified by next logSync.
} while (!editPendingQ.offer(edit));
} finally {
overflowMutex.release(permits);
}
} else {
// mutex will throttle contention during persistent overflow.
overflowMutex.acquire();
try {
editPendingQ.put(edit);
} finally {
overflowMutex.release();
}
}
}
} catch (Throwable t) {
// should never happen! failure to enqueue an edit is fatal
terminate(t);
}
}
private Edit dequeueEdit() throws InterruptedException {
// only block for next edit if no pending syncs.
return syncWaitQ.isEmpty() ? editPendingQ.take() : editPendingQ.poll();
}
@Override
public void run() {
try {
while (true) {
boolean doSync;
Edit edit = dequeueEdit();
if (edit != null) {
// sync if requested by edit log.
doSync = edit.logEdit();
syncWaitQ.add(edit);
} else {
// sync when editq runs dry, but have edits pending a sync.
doSync = !syncWaitQ.isEmpty();
}
if (doSync) {
// normally edit log exceptions cause the NN to terminate, but tests
// relying on ExitUtil.terminate need to see the exception.
RuntimeException syncEx = null;
try {
logSync(getLastWrittenTxId());
} catch (RuntimeException ex) {
syncEx = ex;
}
while ((edit = syncWaitQ.poll()) != null) {
edit.logSyncNotify(syncEx);
}
}
}
} catch (InterruptedException ie) {
LOG.info(Thread.currentThread().getName() + " was interrupted, exiting");
} catch (Throwable t) {
terminate(t);
}
}
private void terminate(Throwable t) {
String message = "Exception while edit logging: "+t.getMessage();
LOG.error(message, t);
ExitUtil.terminate(1, message);
}
private Edit getEditInstance(FSEditLogOp op) {
final Edit edit;
final Server.Call rpcCall = Server.getCurCall().get();
// only rpc calls not explicitly sync'ed on the log will be async.
if (rpcCall != null && !Thread.holdsLock(this)) {
edit = new RpcEdit(this, op, rpcCall);
} else {
edit = new SyncEdit(this, op);
}
return edit;
}
private abstract static class Edit {
final FSEditLog log;
final FSEditLogOp op;
Edit(FSEditLog log, FSEditLogOp op) {
this.log = log;
this.op = op;
}
// return whether edit log wants to sync.
boolean logEdit() {
return log.doEditTransaction(op);
}
// wait for background thread to finish syncing.
abstract void logSyncWait();
// wake up the thread in logSyncWait.
abstract void logSyncNotify(RuntimeException ex);
}
// the calling thread is synchronously waiting for the edit to complete.
private static class SyncEdit extends Edit {
private final Object lock;
private boolean done = false;
private RuntimeException syncEx;
SyncEdit(FSEditLog log, FSEditLogOp op) {
super(log, op);
// if the log is already sync'ed (ex. log rolling), must wait on it to
// avoid deadlock with sync thread. the fsn lock protects against
// logging during a roll. else lock on this object to avoid sync
// contention on edit log.
lock = Thread.holdsLock(log) ? log : this;
}
@Override
public void logSyncWait() {
synchronized(lock) {
while (!done) {
try {
lock.wait(10);
} catch (InterruptedException e) {}
}
// only needed by tests that rely on ExitUtil.terminate() since
// normally exceptions terminate the NN.
if (syncEx != null) {
syncEx.fillInStackTrace();
throw syncEx;
}
}
}
@Override
public void logSyncNotify(RuntimeException ex) {
synchronized(lock) {
done = true;
syncEx = ex;
lock.notifyAll();
}
}
@Override
public String toString() {
return "["+getClass().getSimpleName()+" op:"+op+"]";
}
}
// the calling rpc thread will return immediately from logSync but the
// rpc response will not be sent until the edit is durable.
private static class RpcEdit extends Edit {
private final Server.Call call;
RpcEdit(FSEditLog log, FSEditLogOp op, Server.Call call) {
super(log, op);
this.call = call;
call.postponeResponse();
}
@Override
public void logSyncWait() {
// logSync is a no-op to immediately free up rpc handlers. the
// response is sent when the sync thread calls syncNotify.
}
@Override
public void logSyncNotify(RuntimeException syncEx) {
try {
if (syncEx == null) {
call.sendResponse();
} else {
call.abortResponse(syncEx);
}
} catch (Exception e) {} // don't care if not sent.
}
@Override
public String toString() {
return "["+getClass().getSimpleName()+" op:"+op+" call:"+call+"]";
}
}
}
