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/*
* Copyright 2012 The Netty Project
*
* The Netty Project 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 io.netty.channel.nio;
import io.netty.channel.Channel;
import io.netty.channel.ChannelException;
import io.netty.channel.EventLoopException;
import io.netty.channel.SingleThreadEventLoop;
import io.netty.channel.nio.AbstractNioChannel.NioUnsafe;
import io.netty.util.concurrent.TaskScheduler;
import io.netty.util.internal.SystemPropertyUtil;
import io.netty.util.internal.logging.InternalLogger;
import io.netty.util.internal.logging.InternalLoggerFactory;
import java.io.IOException;
import java.nio.channels.CancelledKeyException;
import java.nio.channels.SelectableChannel;
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.ConcurrentModificationException;
import java.util.Iterator;
import java.util.Queue;
import java.util.Set;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
/**
* {@link SingleThreadEventLoop} implementation which register the {@link Channel}'s to a
* {@link Selector} and so does the multi-plexing of these in the event loop.
*
*/
public final class NioEventLoop extends SingleThreadEventLoop {
/**
* Internal Netty logger.
*/
private static final InternalLogger logger =
InternalLoggerFactory.getInstance(NioEventLoop.class);
private static final int CLEANUP_INTERVAL = 256; // XXX Hard-coded value, but won't need customization.
private static final boolean EPOLL_BUG_WORKAROUND =
SystemPropertyUtil.getBoolean("io.netty.epollBugWorkaround", false);
private static final long SELECT_TIMEOUT = SystemPropertyUtil.getLong("io.netty.selectTimeout", 500);
private static final long SELECT_TIMEOUT_NANOS = TimeUnit.MILLISECONDS.toNanos(SELECT_TIMEOUT);
// Workaround for JDK NIO bug.
//
// See:
// - http://bugs.sun.com/view_bug.do?bug_id=6427854
// - https://github.com/netty/netty/issues/203
static {
String key = "sun.nio.ch.bugLevel";
try {
String buglevel = System.getProperty(key);
if (buglevel == null) {
System.setProperty(key, "");
}
} catch (SecurityException e) {
if (logger.isDebugEnabled()) {
logger.debug("Unable to get/set System Property '" + key + '\'', e);
}
}
if (logger.isDebugEnabled()) {
logger.debug("Using select timeout of " + SELECT_TIMEOUT);
logger.debug("Epoll-bug workaround enabled = " + EPOLL_BUG_WORKAROUND);
}
}
/**
* The NIO {@link Selector}.
*/
Selector selector;
private final SelectorProvider provider;
/**
* Boolean that controls determines if a blocked Selector.select should
* break out of its selection process. In our case we use a timeone for
* the select method and the select method will block for that time unless
* waken up.
*/
private final AtomicBoolean wakenUp = new AtomicBoolean();
private volatile int ioRatio = 50;
private int cancelledKeys;
private boolean cleanedCancelledKeys;
NioEventLoop(
NioEventLoopGroup parent, ThreadFactory threadFactory,
TaskScheduler scheduler, SelectorProvider selectorProvider) {
super(parent, threadFactory, scheduler);
if (selectorProvider == null) {
throw new NullPointerException("selectorProvider");
}
provider = selectorProvider;
selector = openSelector();
}
private Selector openSelector() {
try {
return provider.openSelector();
} catch (IOException e) {
throw new ChannelException("failed to open a new selector", e);
}
}
@Override
protected Queue newTaskQueue() {
// This event loop never calls takeTask()
return new ConcurrentLinkedQueue();
}
/**
* Registers an arbitrary {@link SelectableChannel}, not necessarily created by Netty, to the {@link Selector}
* of this event loop. Once the specified {@link SelectableChannel} is registered, the specified {@code task} will
* be executed by this event loop when the {@link SelectableChannel} is ready.
*/
public void register(final SelectableChannel ch, final int interestOps, final NioTask task) {
if (ch == null) {
throw new NullPointerException("ch");
}
if (interestOps == 0) {
throw new IllegalArgumentException("interestOps must be non-zero.");
}
if ((interestOps & ~ch.validOps()) != 0) {
throw new IllegalArgumentException(
"invalid interestOps: " + interestOps + "(validOps: " + ch.validOps() + ')');
}
if (task == null) {
throw new NullPointerException("task");
}
if (isShutdown()) {
throw new IllegalStateException("event loop shut down");
}
try {
ch.register(selector, interestOps, task);
} catch (Exception e) {
throw new EventLoopException("failed to register a channel", e);
}
}
void executeWhenWritable(AbstractNioChannel channel, NioTask task) {
if (channel == null) {
throw new NullPointerException("channel");
}
if (isShutdown()) {
throw new IllegalStateException("event loop shut down");
}
SelectionKey key = channel.selectionKey();
channel.writableTasks.offer(task);
int interestOps = key.interestOps();
if ((interestOps & SelectionKey.OP_WRITE) == 0) {
key.interestOps(interestOps | SelectionKey.OP_WRITE);
}
}
/**
* Returns the percentage of the desired amount of time spent for I/O in the event loop.
*/
public int getIoRatio() {
return ioRatio;
}
/**
* Sets the percentage of the desired amount of time spent for I/O in the event loop. The default value is
* {@code 50}, which means the event loop will try to spend the same amount of time for I/O as for non-I/O tasks.
*/
public void setIoRatio(int ioRatio) {
if (ioRatio <= 0 || ioRatio >= 100) {
throw new IllegalArgumentException("ioRatio: " + ioRatio + " (expected: 0 < ioRatio < 100)");
}
this.ioRatio = ioRatio;
}
/**
* Replaces the current {@link Selector} of this event loop with newly created {@link Selector}s to work
* around the infamous epoll 100% CPU bug.
*/
public void rebuildSelector() {
if (!inEventLoop()) {
execute(new Runnable() {
@Override
public void run() {
rebuildSelector();
}
});
return;
}
final Selector oldSelector = selector;
final Selector newSelector;
if (oldSelector == null) {
return;
}
try {
newSelector = Selector.open();
} catch (Exception e) {
logger.warn("Failed to create a new Selector.", e);
return;
}
// Register all channels to the new Selector.
int nChannels = 0;
for (;;) {
try {
for (SelectionKey key: oldSelector.keys()) {
Object a = key.attachment();
try {
if (key.channel().keyFor(newSelector) != null) {
continue;
}
int interestOps = key.interestOps();
key.cancel();
key.channel().register(newSelector, interestOps, a);
nChannels ++;
} catch (Exception e) {
logger.warn("Failed to re-register a Channel to the new Selector.", e);
if (a instanceof AbstractNioChannel) {
AbstractNioChannel ch = (AbstractNioChannel) a;
ch.unsafe().close(ch.unsafe().voidFuture());
} else {
@SuppressWarnings("unchecked")
NioTask task = (NioTask) a;
invokeChannelUnregistered(task, key, e);
}
}
}
} catch (ConcurrentModificationException e) {
// Probably due to concurrent modification of the key set.
continue;
}
break;
}
selector = newSelector;
try {
// time to close the old selector as everything else is registered to the new one
oldSelector.close();
} catch (Throwable t) {
if (logger.isWarnEnabled()) {
logger.warn("Failed to close the old Selector.", t);
}
}
logger.info("Migrated " + nChannels + " channel(s) to the new Selector.");
}
@Override
protected void run() {
// use 80% of the timeout for measure
final long minSelectTimeout = SELECT_TIMEOUT_NANOS / 100 * 80;
Selector selector = this.selector;
int selectReturnsImmediately = 0;
for (;;) {
wakenUp.set(false);
try {
if (hasTasks()) {
selectNow();
} else {
long beforeSelect = System.nanoTime();
int selected = select();
if (EPOLL_BUG_WORKAROUND) {
if (selected == 0) {
long timeBlocked = System.nanoTime() - beforeSelect;
if (timeBlocked < minSelectTimeout) {
// returned before the minSelectTimeout elapsed with nothing select.
// this may be the cause of the jdk epoll(..) bug, so increment the counter
// which we use later to see if its really the jdk bug.
selectReturnsImmediately ++;
} else {
selectReturnsImmediately = 0;
}
if (selectReturnsImmediately == 10) {
// The selector returned immediately for 10 times in a row,
// so recreate one selector as it seems like we hit the
// famous epoll(..) jdk bug.
rebuildSelector();
selector = this.selector;
selectReturnsImmediately = 0;
// try to select again
continue;
}
} else {
// reset counter
selectReturnsImmediately = 0;
}
}
// 'wakenUp.compareAndSet(false, true)' is always evaluated
// before calling 'selector.wakeup()' to reduce the wake-up
// overhead. (Selector.wakeup() is an expensive operation.)
//
// However, there is a race condition in this approach.
// The race condition is triggered when 'wakenUp' is set to
// true too early.
//
// 'wakenUp' is set to true too early if:
// 1) Selector is waken up between 'wakenUp.set(false)' and
// 'selector.select(...)'. (BAD)
// 2) Selector is waken up between 'selector.select(...)' and
// 'if (wakenUp.get()) { ... }'. (OK)
//
// In the first case, 'wakenUp' is set to true and the
// following 'selector.select(...)' will wake up immediately.
// Until 'wakenUp' is set to false again in the next round,
// 'wakenUp.compareAndSet(false, true)' will fail, and therefore
// any attempt to wake up the Selector will fail, too, causing
// the following 'selector.select(...)' call to block
// unnecessarily.
//
// To fix this problem, we wake up the selector again if wakenUp
// is true immediately after selector.select(...).
// It is inefficient in that it wakes up the selector for both
// the first case (BAD - wake-up required) and the second case
// (OK - no wake-up required).
if (wakenUp.get()) {
selector.wakeup();
}
}
cancelledKeys = 0;
final long ioStartTime = System.nanoTime();
processSelectedKeys();
selector = this.selector;
final long ioTime = System.nanoTime() - ioStartTime;
final int ioRatio = this.ioRatio;
runAllTasks(ioTime * (100 - ioRatio) / ioRatio);
selector = this.selector;
if (isShutdown()) {
closeAll();
if (confirmShutdown()) {
break;
}
}
} catch (Throwable t) {
logger.warn("Unexpected exception in the selector loop.", t);
// Prevent possible consecutive immediate failures that lead to
// excessive CPU consumption.
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// Ignore.
}
}
}
}
@Override
protected void cleanup() {
try {
selector.close();
} catch (IOException e) {
logger.warn("Failed to close a selector.", e);
}
}
void cancel(SelectionKey key) {
key.cancel();
cancelledKeys ++;
if (cancelledKeys >= CLEANUP_INTERVAL) {
cancelledKeys = 0;
cleanedCancelledKeys = true;
cleanupKeys();
}
}
private void processSelectedKeys() {
Set selectedKeys = selector.selectedKeys();
// check if the set is empty and if so just return to not create garbage by
// creating a new Iterator every time even if there is nothing to process.
// See https://github.com/netty/netty/issues/597
if (selectedKeys.isEmpty()) {
return;
}
Iterator i;
cleanedCancelledKeys = false;
boolean clearSelectedKeys = true;
try {
for (i = selectedKeys.iterator(); i.hasNext();) {
final SelectionKey k = i.next();
final Object a = k.attachment();
if (a instanceof AbstractNioChannel) {
processSelectedKey(k, (AbstractNioChannel) a);
} else {
@SuppressWarnings("unchecked")
NioTask task = (NioTask) a;
processSelectedKey(k, task);
}
if (cleanedCancelledKeys) {
// Create the iterator again to avoid ConcurrentModificationException
if (selectedKeys.isEmpty()) {
clearSelectedKeys = false;
break;
} else {
i = selectedKeys.iterator();
}
}
}
} finally {
if (clearSelectedKeys) {
selectedKeys.clear();
}
}
}
private static void processSelectedKey(SelectionKey k, AbstractNioChannel ch) {
final NioUnsafe unsafe = ch.unsafe();
if (!k.isValid()) {
// close the channel if the key is not valid anymore
unsafe.close(unsafe.voidFuture());
return;
}
int readyOps = -1;
try {
readyOps = k.readyOps();
if ((readyOps & (SelectionKey.OP_READ | SelectionKey.OP_ACCEPT)) != 0 || readyOps == 0) {
unsafe.read();
if (!ch.isOpen()) {
// Connection already closed - no need to handle write.
return;
}
}
if ((readyOps & SelectionKey.OP_WRITE) != 0) {
processWritable(k, ch);
}
if ((readyOps & SelectionKey.OP_CONNECT) != 0) {
// remove OP_CONNECT as otherwise Selector.select(..) will always return without blocking
// See https://github.com/netty/netty/issues/924
int ops = k.interestOps();
ops &= ~SelectionKey.OP_CONNECT;
k.interestOps(ops);
unsafe.finishConnect();
}
} catch (CancelledKeyException e) {
if (readyOps != -1 && (readyOps & SelectionKey.OP_WRITE) != 0) {
unregisterWritableTasks(ch);
}
unsafe.close(unsafe.voidFuture());
}
}
private static void processWritable(SelectionKey k, AbstractNioChannel ch) {
if (ch.writableTasks.isEmpty()) {
ch.unsafe().flushNow();
} else {
NioTask task;
for (;;) {
task = ch.writableTasks.poll();
if (task == null) { break; }
processSelectedKey(ch.selectionKey(), task);
}
k.interestOps(k.interestOps() | SelectionKey.OP_WRITE);
}
}
private static void unregisterWritableTasks(AbstractNioChannel ch) {
NioTask task;
for (;;) {
task = ch.writableTasks.poll();
if (task == null) {
break;
} else {
invokeChannelUnregistered(task, ch.selectionKey(), null);
}
}
}
private static void processSelectedKey(SelectionKey k, NioTask task) {
int state = 0;
try {
task.channelReady(k.channel(), k);
state = 1;
} catch (Exception e) {
k.cancel();
invokeChannelUnregistered(task, k, e);
state = 2;
} finally {
switch (state) {
case 0:
k.cancel();
invokeChannelUnregistered(task, k, null);
break;
case 1:
if (!k.isValid()) { // Cancelled by channelReady()
invokeChannelUnregistered(task, k, null);
}
break;
}
}
}
private void closeAll() {
cleanupKeys();
Set keys = selector.keys();
Collection channels = new ArrayList(keys.size());
for (SelectionKey k: keys) {
Object a = k.attachment();
if (a instanceof AbstractNioChannel) {
channels.add((AbstractNioChannel) a);
} else {
k.cancel();
@SuppressWarnings("unchecked")
NioTask task = (NioTask) a;
invokeChannelUnregistered(task, k, null);
}
}
for (AbstractNioChannel ch: channels) {
unregisterWritableTasks(ch);
ch.unsafe().close(ch.unsafe().voidFuture());
}
}
private static void invokeChannelUnregistered(NioTask task, SelectionKey k, Throwable cause) {
try {
task.channelUnregistered(k.channel(), cause);
} catch (Exception e) {
logger.warn("Unexpected exception while running NioTask.channelUnregistered()", e);
}
}
@Override
protected void wakeup(boolean inEventLoop) {
if (!inEventLoop && wakenUp.compareAndSet(false, true)) {
selector.wakeup();
}
}
void selectNow() throws IOException {
try {
selector.selectNow();
} finally {
// restore wakup state if needed
if (wakenUp.get()) {
selector.wakeup();
}
}
}
private int select() throws IOException {
try {
return selector.select(SELECT_TIMEOUT);
} catch (CancelledKeyException e) {
if (logger.isDebugEnabled()) {
logger.debug(
CancelledKeyException.class.getSimpleName() +
" raised by a Selector - JDK bug?", e);
}
// Harmless exception - log anyway
}
return -1;
}
void cleanupKeys() {
try {
selector.selectNow();
} catch (Throwable t) {
logger.warn("Failed to update SelectionKeys.", t);
}
}
}
