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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 libthrift091.server;
import java.io.IOException;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.spi.SelectorProvider;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.TimeUnit;
import libthrift091.transport.TNonblockingServerTransport;
import libthrift091.transport.TNonblockingTransport;
import libthrift091.transport.TTransportException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* A Half-Sync/Half-Async server with a separate pool of threads to handle
* non-blocking I/O. Accepts are handled on a single thread, and a configurable
* number of nonblocking selector threads manage reading and writing of client
* connections. A synchronous worker thread pool handles processing of requests.
*
* Performs better than TNonblockingServer/THsHaServer in multi-core
* environments when the the bottleneck is CPU on the single selector thread
* handling I/O. In addition, because the accept handling is decoupled from
* reads/writes and invocation, the server has better ability to handle back-
* pressure from new connections (e.g. stop accepting when busy).
*
* Like TNonblockingServer, it relies on the use of TFramedTransport.
*/
public class TThreadedSelectorServer extends AbstractNonblockingServer {
private static final Logger LOGGER = LoggerFactory.getLogger(TThreadedSelectorServer.class.getName());
public static class Args extends AbstractNonblockingServerArgs {
/** The number of threads for selecting on already-accepted connections */
public int selectorThreads = 2;
/**
* The size of the executor service (if none is specified) that will handle
* invocations. This may be set to 0, in which case invocations will be
* handled directly on the selector threads (as is in TNonblockingServer)
*/
private int workerThreads = 5;
/** Time to wait for server to stop gracefully */
private int stopTimeoutVal = 60;
private TimeUnit stopTimeoutUnit = TimeUnit.SECONDS;
/** The ExecutorService for handling dispatched requests */
private ExecutorService executorService = null;
/**
* The size of the blocking queue per selector thread for passing accepted
* connections to the selector thread
*/
private int acceptQueueSizePerThread = 4;
/**
* Determines the strategy for handling new accepted connections.
*/
public static enum AcceptPolicy {
/**
* Require accepted connection registration to be handled by the executor.
* If the worker pool is saturated, further accepts will be closed
* immediately. Slightly increases latency due to an extra scheduling.
*/
FAIR_ACCEPT,
/**
* Handle the accepts as fast as possible, disregarding the status of the
* executor service.
*/
FAST_ACCEPT
}
private AcceptPolicy acceptPolicy = AcceptPolicy.FAST_ACCEPT;
public Args(TNonblockingServerTransport transport) {
super(transport);
}
public Args selectorThreads(int i) {
selectorThreads = i;
return this;
}
public int getSelectorThreads() {
return selectorThreads;
}
public Args workerThreads(int i) {
workerThreads = i;
return this;
}
public int getWorkerThreads() {
return workerThreads;
}
public int getStopTimeoutVal() {
return stopTimeoutVal;
}
public Args stopTimeoutVal(int stopTimeoutVal) {
this.stopTimeoutVal = stopTimeoutVal;
return this;
}
public TimeUnit getStopTimeoutUnit() {
return stopTimeoutUnit;
}
public Args stopTimeoutUnit(TimeUnit stopTimeoutUnit) {
this.stopTimeoutUnit = stopTimeoutUnit;
return this;
}
public ExecutorService getExecutorService() {
return executorService;
}
public Args executorService(ExecutorService executorService) {
this.executorService = executorService;
return this;
}
public int getAcceptQueueSizePerThread() {
return acceptQueueSizePerThread;
}
public Args acceptQueueSizePerThread(int acceptQueueSizePerThread) {
this.acceptQueueSizePerThread = acceptQueueSizePerThread;
return this;
}
public AcceptPolicy getAcceptPolicy() {
return acceptPolicy;
}
public Args acceptPolicy(AcceptPolicy acceptPolicy) {
this.acceptPolicy = acceptPolicy;
return this;
}
public void validate() {
if (selectorThreads <= 0) {
throw new IllegalArgumentException("selectorThreads must be positive.");
}
if (workerThreads < 0) {
throw new IllegalArgumentException("workerThreads must be non-negative.");
}
if (acceptQueueSizePerThread <= 0) {
throw new IllegalArgumentException("acceptQueueSizePerThread must be positive.");
}
}
}
// Flag for stopping the server
// Please see THRIFT-1795 for the usage of this flag
private volatile boolean stopped_ = false;
// The thread handling all accepts
private AcceptThread acceptThread;
// Threads handling events on client transports
private final Set selectorThreads = new HashSet();
// This wraps all the functionality of queueing and thread pool management
// for the passing of Invocations from the selector thread(s) to the workers
// (if any).
private final ExecutorService invoker;
private final Args args;
/**
* Create the server with the specified Args configuration
*/
public TThreadedSelectorServer(Args args) {
super(args);
args.validate();
invoker = args.executorService == null ? createDefaultExecutor(args) : args.executorService;
this.args = args;
}
/**
* Start the accept and selector threads running to deal with clients.
*
* @return true if everything went ok, false if we couldn't start for some
* reason.
*/
@Override
protected boolean startThreads() {
try {
for (int i = 0; i < args.selectorThreads; ++i) {
selectorThreads.add(new SelectorThread(args.acceptQueueSizePerThread));
}
acceptThread = new AcceptThread((TNonblockingServerTransport) serverTransport_,
createSelectorThreadLoadBalancer(selectorThreads));
for (SelectorThread thread : selectorThreads) {
thread.start();
}
acceptThread.start();
return true;
} catch (IOException e) {
LOGGER.error("Failed to start threads!", e);
return false;
}
}
/**
* Joins the accept and selector threads and shuts down the executor service.
*/
@Override
protected void waitForShutdown() {
try {
joinThreads();
} catch (InterruptedException e) {
// Non-graceful shutdown occurred
LOGGER.error("Interrupted while joining threads!", e);
}
gracefullyShutdownInvokerPool();
}
protected void joinThreads() throws InterruptedException {
// wait until the io threads exit
acceptThread.join();
for (SelectorThread thread : selectorThreads) {
thread.join();
}
}
/**
* Stop serving and shut everything down.
*/
@Override
public void stop() {
stopped_ = true;
// Stop queuing connect attempts asap
stopListening();
if (acceptThread != null) {
acceptThread.wakeupSelector();
}
if (selectorThreads != null) {
for (SelectorThread thread : selectorThreads) {
if (thread != null)
thread.wakeupSelector();
}
}
}
protected void gracefullyShutdownInvokerPool() {
// try to gracefully shut down the executor service
invoker.shutdown();
// Loop until awaitTermination finally does return without a interrupted
// exception. If we don't do this, then we'll shut down prematurely. We want
// to let the executorService clear it's task queue, closing client sockets
// appropriately.
long timeoutMS = args.stopTimeoutUnit.toMillis(args.stopTimeoutVal);
long now = System.currentTimeMillis();
while (timeoutMS >= 0) {
try {
invoker.awaitTermination(timeoutMS, TimeUnit.MILLISECONDS);
break;
} catch (InterruptedException ix) {
long newnow = System.currentTimeMillis();
timeoutMS -= (newnow - now);
now = newnow;
}
}
}
/**
* We override the standard invoke method here to queue the invocation for
* invoker service instead of immediately invoking. If there is no thread
* pool, handle the invocation inline on this thread
*/
@Override
protected boolean requestInvoke(FrameBuffer frameBuffer) {
Runnable invocation = getRunnable(frameBuffer);
if (invoker != null) {
try {
invoker.execute(invocation);
return true;
} catch (RejectedExecutionException rx) {
LOGGER.warn("ExecutorService rejected execution!", rx);
return false;
}
} else {
// Invoke on the caller's thread
invocation.run();
return true;
}
}
protected Runnable getRunnable(FrameBuffer frameBuffer) {
return new Invocation(frameBuffer);
}
/**
* Helper to create the invoker if one is not specified
*/
protected static ExecutorService createDefaultExecutor(Args options) {
return (options.workerThreads > 0) ? Executors.newFixedThreadPool(options.workerThreads) : null;
}
private static BlockingQueue createDefaultAcceptQueue(int queueSize) {
if (queueSize == 0) {
// Unbounded queue
return new LinkedBlockingQueue();
}
return new ArrayBlockingQueue(queueSize);
}
/**
* The thread that selects on the server transport (listen socket) and accepts
* new connections to hand off to the IO selector threads
*/
protected class AcceptThread extends Thread {
// The listen socket to accept on
private final TNonblockingServerTransport serverTransport;
private final Selector acceptSelector;
private final SelectorThreadLoadBalancer threadChooser;
/**
* Set up the AcceptThead
*
* @throws IOException
*/
public AcceptThread(TNonblockingServerTransport serverTransport,
SelectorThreadLoadBalancer threadChooser) throws IOException {
this.serverTransport = serverTransport;
this.threadChooser = threadChooser;
this.acceptSelector = SelectorProvider.provider().openSelector();
this.serverTransport.registerSelector(acceptSelector);
}
/**
* The work loop. Selects on the server transport and accepts. If there was
* a server transport that had blocking accepts, and returned on blocking
* client transports, that should be used instead
*/
public void run() {
try {
if (eventHandler_ != null) {
eventHandler_.preServe();
}
while (!stopped_) {
select();
}
} catch (Throwable t) {
LOGGER.error("run() exiting due to uncaught error", t);
} finally {
// This will wake up the selector threads
TThreadedSelectorServer.this.stop();
}
}
/**
* If the selector is blocked, wake it up.
*/
public void wakeupSelector() {
acceptSelector.wakeup();
}
/**
* Select and process IO events appropriately: If there are connections to
* be accepted, accept them.
*/
private void select() {
try {
// wait for connect events.
acceptSelector.select();
// process the io events we received
Iterator selectedKeys = acceptSelector.selectedKeys().iterator();
while (!stopped_ && selectedKeys.hasNext()) {
SelectionKey key = selectedKeys.next();
selectedKeys.remove();
// skip if not valid
if (!key.isValid()) {
continue;
}
if (key.isAcceptable()) {
handleAccept();
} else {
LOGGER.warn("Unexpected state in select! " + key.interestOps());
}
}
} catch (IOException e) {
LOGGER.warn("Got an IOException while selecting!", e);
}
}
/**
* Accept a new connection.
*/
private void handleAccept() {
final TNonblockingTransport client = doAccept();
if (client != null) {
// Pass this connection to a selector thread
final SelectorThread targetThread = threadChooser.nextThread();
if (args.acceptPolicy == Args.AcceptPolicy.FAST_ACCEPT || invoker == null) {
doAddAccept(targetThread, client);
} else {
// FAIR_ACCEPT
try {
invoker.submit(new Runnable() {
public void run() {
doAddAccept(targetThread, client);
}
});
} catch (RejectedExecutionException rx) {
LOGGER.warn("ExecutorService rejected accept registration!", rx);
// close immediately
client.close();
}
}
}
}
private TNonblockingTransport doAccept() {
try {
return (TNonblockingTransport) serverTransport.accept();
} catch (TTransportException tte) {
// something went wrong accepting.
LOGGER.warn("Exception trying to accept!", tte);
return null;
}
}
private void doAddAccept(SelectorThread thread, TNonblockingTransport client) {
if (!thread.addAcceptedConnection(client)) {
client.close();
}
}
} // AcceptThread
/**
* The SelectorThread(s) will be doing all the selecting on accepted active
* connections.
*/
protected class SelectorThread extends AbstractSelectThread {
// Accepted connections added by the accept thread.
private final BlockingQueue acceptedQueue;
/**
* Set up the SelectorThread with an unbounded queue for incoming accepts.
*
* @throws IOException
* if a selector cannot be created
*/
public SelectorThread() throws IOException {
this(new LinkedBlockingQueue());
}
/**
* Set up the SelectorThread with an bounded queue for incoming accepts.
*
* @throws IOException
* if a selector cannot be created
*/
public SelectorThread(int maxPendingAccepts) throws IOException {
this(createDefaultAcceptQueue(maxPendingAccepts));
}
/**
* Set up the SelectorThread with a specified queue for connections.
*
* @param acceptedQueue
* The BlockingQueue implementation for holding incoming accepted
* connections.
* @throws IOException
* if a selector cannot be created.
*/
public SelectorThread(BlockingQueue acceptedQueue) throws IOException {
this.acceptedQueue = acceptedQueue;
}
/**
* Hands off an accepted connection to be handled by this thread. This
* method will block if the queue for new connections is at capacity.
*
* @param accepted
* The connection that has been accepted.
* @return true if the connection has been successfully added.
*/
public boolean addAcceptedConnection(TNonblockingTransport accepted) {
try {
acceptedQueue.put(accepted);
} catch (InterruptedException e) {
LOGGER.warn("Interrupted while adding accepted connection!", e);
return false;
}
selector.wakeup();
return true;
}
/**
* The work loop. Handles selecting (read/write IO), dispatching, and
* managing the selection preferences of all existing connections.
*/
public void run() {
try {
while (!stopped_) {
select();
processAcceptedConnections();
processInterestChanges();
}
for (SelectionKey selectionKey : selector.keys()) {
cleanupSelectionKey(selectionKey);
}
} catch (Throwable t) {
LOGGER.error("run() exiting due to uncaught error", t);
} finally {
// This will wake up the accept thread and the other selector threads
TThreadedSelectorServer.this.stop();
}
}
/**
* Select and process IO events appropriately: If there are existing
* connections with data waiting to be read, read it, buffering until a
* whole frame has been read. If there are any pending responses, buffer
* them until their target client is available, and then send the data.
*/
private void select() {
try {
// wait for io events.
selector.select();
// process the io events we received
Iterator selectedKeys = selector.selectedKeys().iterator();
while (!stopped_ && selectedKeys.hasNext()) {
SelectionKey key = selectedKeys.next();
selectedKeys.remove();
// skip if not valid
if (!key.isValid()) {
cleanupSelectionKey(key);
continue;
}
if (key.isReadable()) {
// deal with reads
handleRead(key);
} else if (key.isWritable()) {
// deal with writes
handleWrite(key);
} else {
LOGGER.warn("Unexpected state in select! " + key.interestOps());
}
}
} catch (IOException e) {
LOGGER.warn("Got an IOException while selecting!", e);
}
}
private void processAcceptedConnections() {
// Register accepted connections
while (!stopped_) {
TNonblockingTransport accepted = acceptedQueue.poll();
if (accepted == null) {
break;
}
registerAccepted(accepted);
}
}
private void registerAccepted(TNonblockingTransport accepted) {
SelectionKey clientKey = null;
try {
clientKey = accepted.registerSelector(selector, SelectionKey.OP_READ);
FrameBuffer frameBuffer = processorFactory_.isAsyncProcessor() ?
new AsyncFrameBuffer(accepted, clientKey, SelectorThread.this) :
new FrameBuffer(accepted, clientKey, SelectorThread.this);
clientKey.attach(frameBuffer);
} catch (IOException e) {
LOGGER.warn("Failed to register accepted connection to selector!", e);
if (clientKey != null) {
cleanupSelectionKey(clientKey);
}
accepted.close();
}
}
} // SelectorThread
/**
* Creates a SelectorThreadLoadBalancer to be used by the accept thread for
* assigning newly accepted connections across the threads.
*/
protected SelectorThreadLoadBalancer createSelectorThreadLoadBalancer(Collection threads) {
return new SelectorThreadLoadBalancer(threads);
}
/**
* A round robin load balancer for choosing selector threads for new
* connections.
*/
protected class SelectorThreadLoadBalancer {
private final Collection threads;
private Iterator nextThreadIterator;
public SelectorThreadLoadBalancer(Collection threads) {
if (threads.isEmpty()) {
throw new IllegalArgumentException("At least one selector thread is required");
}
this.threads = Collections.unmodifiableList(new ArrayList(threads));
nextThreadIterator = this.threads.iterator();
}
public SelectorThread nextThread() {
// Choose a selector thread (round robin)
if (!nextThreadIterator.hasNext()) {
nextThreadIterator = threads.iterator();
}
return nextThreadIterator.next();
}
}
}
