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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.shortcircuit;
import java.io.BufferedOutputStream;
import java.io.Closeable;
import java.io.DataOutputStream;
import java.io.EOFException;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map.Entry;
import java.util.TreeMap;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
import org.apache.commons.lang3.mutable.MutableBoolean;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.hdfs.ExtendedBlockId;
import org.apache.hadoop.hdfs.net.DomainPeer;
import org.apache.hadoop.hdfs.protocol.DatanodeInfo;
import org.apache.hadoop.hdfs.protocol.datatransfer.DataTransferProtocol;
import org.apache.hadoop.hdfs.protocol.datatransfer.Sender;
import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.ShortCircuitShmResponseProto;
import org.apache.hadoop.hdfs.protocolPB.PBHelperClient;
import org.apache.hadoop.hdfs.shortcircuit.ShortCircuitShm.ShmId;
import org.apache.hadoop.hdfs.shortcircuit.ShortCircuitShm.Slot;
import org.apache.hadoop.net.unix.DomainSocket;
import org.apache.hadoop.net.unix.DomainSocketWatcher;
import org.apache.hadoop.classification.VisibleForTesting;
import org.apache.hadoop.util.Preconditions;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Manages short-circuit memory segments for an HDFS client.
*
* Clients are responsible for requesting and releasing shared memory segments
* used for communicating with the DataNode. The client will try to allocate new
* slots in the set of existing segments, falling back to getting a new segment
* from the DataNode via {@link DataTransferProtocol#requestShortCircuitFds}.
*
* The counterpart to this class on the DataNode is ShortCircuitRegistry.
* See ShortCircuitRegistry for more information on the communication protocol.
*/
@InterfaceAudience.Private
public class DfsClientShmManager implements Closeable {
private static final Logger LOG = LoggerFactory.getLogger(
DfsClientShmManager.class);
/**
* Manages short-circuit memory segments that pertain to a given DataNode.
*/
class EndpointShmManager {
/**
* The datanode we're managing.
*/
private final DatanodeInfo datanode;
/**
* Shared memory segments which have no empty slots.
*
* Protected by the manager lock.
*/
private final TreeMap full = new TreeMap<>();
/**
* Shared memory segments which have at least one empty slot.
*
* Protected by the manager lock.
*/
private final TreeMap notFull = new TreeMap<>();
/**
* True if this datanode doesn't support short-circuit shared memory
* segments.
*
* Protected by the manager lock.
*/
private boolean disabled = false;
/**
* True if we're in the process of loading a shared memory segment from
* this DataNode.
*
* Protected by the manager lock.
*/
private boolean loading = false;
EndpointShmManager (DatanodeInfo datanode) {
this.datanode = datanode;
}
/**
* Pull a slot out of a preexisting shared memory segment.
*
* Must be called with the manager lock held.
*
* @param blockId The blockId to put inside the Slot object.
*
* @return null if none of our shared memory segments contain a
* free slot; the slot object otherwise.
*/
private Slot allocSlotFromExistingShm(ExtendedBlockId blockId) {
if (notFull.isEmpty()) {
return null;
}
Entry entry = notFull.firstEntry();
DfsClientShm shm = entry.getValue();
ShmId shmId = shm.getShmId();
Slot slot = shm.allocAndRegisterSlot(blockId);
if (shm.isFull()) {
LOG.trace("{}: pulled the last slot {} out of {}",
this, slot.getSlotIdx(), shm);
DfsClientShm removedShm = notFull.remove(shmId);
Preconditions.checkState(removedShm == shm);
full.put(shmId, shm);
} else {
LOG.trace("{}: pulled slot {} out of {}", this, slot.getSlotIdx(), shm);
}
return slot;
}
/**
* Ask the DataNode for a new shared memory segment. This function must be
* called with the manager lock held. We will release the lock while
* communicating with the DataNode.
*
* @param clientName The current client name.
* @param peer The peer to use to talk to the DataNode.
*
* @return Null if the DataNode does not support shared memory
* segments, or experienced an error creating the
* shm. The shared memory segment itself on success.
* @throws IOException If there was an error communicating over the socket.
* We will not throw an IOException unless the socket
* itself (or the network) is the problem.
*/
private DfsClientShm requestNewShm(String clientName, DomainPeer peer)
throws IOException {
final DataOutputStream out =
new DataOutputStream(
new BufferedOutputStream(peer.getOutputStream()));
new Sender(out).requestShortCircuitShm(clientName);
ShortCircuitShmResponseProto resp =
ShortCircuitShmResponseProto.parseFrom(
PBHelperClient.vintPrefixed(peer.getInputStream()));
String error = resp.hasError() ? resp.getError() : "(unknown)";
switch (resp.getStatus()) {
case SUCCESS:
DomainSocket sock = peer.getDomainSocket();
byte buf[] = new byte[1];
FileInputStream[] fis = new FileInputStream[1];
if (sock.recvFileInputStreams(fis, buf, 0, buf.length) < 0) {
throw new EOFException("got EOF while trying to transfer the " +
"file descriptor for the shared memory segment.");
}
if (fis[0] == null) {
throw new IOException("the datanode " + datanode + " failed to " +
"pass a file descriptor for the shared memory segment.");
}
try {
DfsClientShm shm =
new DfsClientShm(PBHelperClient.convert(resp.getId()),
fis[0], this, peer);
LOG.trace("{}: createNewShm: created {}", this, shm);
return shm;
} finally {
try {
fis[0].close();
} catch (Throwable e) {
LOG.debug("Exception in closing " + fis[0], e);
}
}
case ERROR_UNSUPPORTED:
// The DataNode just does not support short-circuit shared memory
// access, and we should stop asking.
LOG.info(this + ": datanode does not support short-circuit " +
"shared memory access: " + error);
disabled = true;
return null;
default:
// The datanode experienced some kind of unexpected error when trying to
// create the short-circuit shared memory segment.
LOG.warn(this + ": error requesting short-circuit shared memory " +
"access: " + error);
return null;
}
}
/**
* Allocate a new shared memory slot connected to this datanode.
*
* Must be called with the EndpointShmManager lock held.
*
* @param peer The peer to use to talk to the DataNode.
* @param usedPeer (out param) Will be set to true if we used the peer.
* When a peer is used
*
* @param clientName The client name.
* @param blockId The block ID to use.
* @return null if the DataNode does not support shared memory
* segments, or experienced an error creating the
* shm. The shared memory segment itself on success.
* @throws IOException If there was an error communicating over the socket.
*/
Slot allocSlot(DomainPeer peer, MutableBoolean usedPeer,
String clientName, ExtendedBlockId blockId) throws IOException {
while (true) {
if (closed) {
LOG.trace("{}: the DfsClientShmManager has been closed.", this);
return null;
}
if (disabled) {
LOG.trace("{}: shared memory segment access is disabled.", this);
return null;
}
// Try to use an existing slot.
Slot slot = allocSlotFromExistingShm(blockId);
if (slot != null) {
return slot;
}
// There are no free slots. If someone is loading more slots, wait
// for that to finish.
if (loading) {
LOG.trace("{}: waiting for loading to finish...", this);
finishedLoading.awaitUninterruptibly();
} else {
// Otherwise, load the slot ourselves.
loading = true;
lock.unlock();
DfsClientShm shm;
try {
shm = requestNewShm(clientName, peer);
if (shm == null) continue;
// See #{DfsClientShmManager#domainSocketWatcher} for details
// about why we do this before retaking the manager lock.
domainSocketWatcher.add(peer.getDomainSocket(), shm);
// The DomainPeer is now our responsibility, and should not be
// closed by the caller.
usedPeer.setValue(true);
} finally {
lock.lock();
loading = false;
finishedLoading.signalAll();
}
if (shm.isDisconnected()) {
// If the peer closed immediately after the shared memory segment
// was created, the DomainSocketWatcher callback might already have
// fired and marked the shm as disconnected. In this case, we
// obviously don't want to add the SharedMemorySegment to our list
// of valid not-full segments.
LOG.debug("{}: the UNIX domain socket associated with this "
+ "short-circuit memory closed before we could make use of "
+ "the shm.", this);
} else {
notFull.put(shm.getShmId(), shm);
}
}
}
}
/**
* Stop tracking a slot.
*
* Must be called with the EndpointShmManager lock held.
*
* @param slot The slot to release.
*/
void freeSlot(Slot slot) {
DfsClientShm shm = (DfsClientShm)slot.getShm();
shm.unregisterSlot(slot.getSlotIdx());
if (shm.isDisconnected()) {
// Stale shared memory segments should not be tracked here.
Preconditions.checkState(!full.containsKey(shm.getShmId()));
Preconditions.checkState(!notFull.containsKey(shm.getShmId()));
if (shm.isEmpty()) {
LOG.trace("{}: freeing empty stale {}", this, shm);
shm.free();
}
} else {
ShmId shmId = shm.getShmId();
full.remove(shmId); // The shm can't be full if we just freed a slot.
if (shm.isEmpty()) {
notFull.remove(shmId);
// If the shared memory segment is now empty, we call shutdown(2) on
// the UNIX domain socket associated with it. The DomainSocketWatcher,
// which is watching this socket, will call DfsClientShm#handle,
// cleaning up this shared memory segment.
//
// See #{DfsClientShmManager#domainSocketWatcher} for details about why
// we don't want to call DomainSocketWatcher#remove directly here.
//
// Note that we could experience 'fragmentation' here, where the
// DFSClient allocates a bunch of slots in different shared memory
// segments, and then frees most of them, but never fully empties out
// any segment. We make some attempt to avoid this fragmentation by
// always allocating new slots out of the shared memory segment with the
// lowest ID, but it could still occur. In most workloads,
// fragmentation should not be a major concern, since it doesn't impact
// peak file descriptor usage or the speed of allocation.
LOG.trace("{}: shutting down UNIX domain socket for empty {}",
this, shm);
shutdown(shm);
} else {
notFull.put(shmId, shm);
}
}
}
/**
* Unregister a shared memory segment.
*
* Once a segment is unregistered, we will not allocate any more slots
* inside that segment.
*
* The DomainSocketWatcher calls this while holding the DomainSocketWatcher
* lock.
*
* @param shmId The ID of the shared memory segment to unregister.
*/
void unregisterShm(ShmId shmId) {
lock.lock();
try {
full.remove(shmId);
notFull.remove(shmId);
} finally {
lock.unlock();
}
}
@Override
public String toString() {
return String.format("EndpointShmManager(%s, parent=%s)",
datanode, DfsClientShmManager.this);
}
PerDatanodeVisitorInfo getVisitorInfo() {
return new PerDatanodeVisitorInfo(full, notFull, disabled);
}
final void shutdown(DfsClientShm shm) {
try {
shm.getPeer().getDomainSocket().shutdown();
} catch (IOException e) {
LOG.warn(this + ": error shutting down shm: got IOException calling " +
"shutdown(SHUT_RDWR)", e);
}
}
}
private boolean closed = false;
private final ReentrantLock lock = new ReentrantLock();
/**
* A condition variable which is signalled when we finish loading a segment
* from the Datanode.
*/
private final Condition finishedLoading = lock.newCondition();
/**
* Information about each Datanode.
*/
private final HashMap datanodes =
new HashMap<>(1);
/**
* The DomainSocketWatcher which keeps track of the UNIX domain socket
* associated with each shared memory segment.
*
* Note: because the DomainSocketWatcher makes callbacks into this
* DfsClientShmManager object, you must MUST NOT attempt to take the
* DomainSocketWatcher lock while holding the DfsClientShmManager lock,
* or else deadlock might result. This means that most DomainSocketWatcher
* methods are off-limits unless you release the manager lock first.
*/
private final DomainSocketWatcher domainSocketWatcher;
DfsClientShmManager(int interruptCheckPeriodMs) throws IOException {
this.domainSocketWatcher = new DomainSocketWatcher(interruptCheckPeriodMs,
"client");
}
public Slot allocSlot(DatanodeInfo datanode, DomainPeer peer,
MutableBoolean usedPeer, ExtendedBlockId blockId,
String clientName) throws IOException {
lock.lock();
try {
if (closed) {
LOG.trace(this + ": the DfsClientShmManager isclosed.");
return null;
}
EndpointShmManager shmManager = datanodes.get(datanode);
if (shmManager == null) {
shmManager = new EndpointShmManager(datanode);
datanodes.put(datanode, shmManager);
}
return shmManager.allocSlot(peer, usedPeer, clientName, blockId);
} finally {
lock.unlock();
}
}
public void freeSlot(Slot slot) {
lock.lock();
try {
DfsClientShm shm = (DfsClientShm)slot.getShm();
shm.getEndpointShmManager().freeSlot(slot);
} finally {
lock.unlock();
}
}
@VisibleForTesting
public static class PerDatanodeVisitorInfo {
public final TreeMap full;
public final TreeMap notFull;
public final boolean disabled;
PerDatanodeVisitorInfo(TreeMap full,
TreeMap notFull, boolean disabled) {
this.full = full;
this.notFull = notFull;
this.disabled = disabled;
}
}
@VisibleForTesting
public interface Visitor {
void visit(HashMap info)
throws IOException;
}
@VisibleForTesting
public void visit(Visitor visitor) throws IOException {
lock.lock();
try {
HashMap info = new HashMap<>();
for (Entry entry :
datanodes.entrySet()) {
info.put(entry.getKey(), entry.getValue().getVisitorInfo());
}
visitor.visit(info);
} finally {
lock.unlock();
}
}
/**
* Close the DfsClientShmManager.
*/
@Override
public void close() throws IOException {
lock.lock();
try {
if (closed) return;
closed = true;
} finally {
lock.unlock();
}
// When closed, the domainSocketWatcher will issue callbacks that mark
// all the outstanding DfsClientShm segments as stale.
try {
domainSocketWatcher.close();
} catch (Throwable e) {
LOG.debug("Exception in closing " + domainSocketWatcher, e);
}
}
@Override
public String toString() {
return String.format("ShortCircuitShmManager(%08x)",
System.identityHashCode(this));
}
@VisibleForTesting
public DomainSocketWatcher getDomainSocketWatcher() {
return domainSocketWatcher;
}
@VisibleForTesting
public int getShmNum() {
int segments = 0;
for (EndpointShmManager endpointShmManager : datanodes.values()) {
segments +=
endpointShmManager.notFull.size() + endpointShmManager.full.size();
}
return segments;
}
}
