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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.net;
import java.io.IOException;
import java.io.InterruptedIOException;
import java.net.SocketAddress;
import java.net.SocketTimeoutException;
import java.nio.ByteBuffer;
import java.nio.channels.SelectableChannel;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;
import java.nio.channels.spi.SelectorProvider;
import java.util.Iterator;
import java.util.LinkedList;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.util.StringUtils;
/**
* This supports input and output streams for a socket channels.
* These streams can have a timeout.
*/
abstract class SocketIOWithTimeout {
// This is intentionally package private.
static final Log LOG = LogFactory.getLog(SocketIOWithTimeout.class);
private SelectableChannel channel;
private long timeout;
private boolean closed = false;
private static SelectorPool selector = new SelectorPool();
/* A timeout value of 0 implies wait for ever.
* We should have a value of timeout that implies zero wait.. i.e.
* read or write returns immediately.
*
* This will set channel to non-blocking.
*/
SocketIOWithTimeout(SelectableChannel channel, long timeout)
throws IOException {
checkChannelValidity(channel);
this.channel = channel;
this.timeout = timeout;
// Set non-blocking
channel.configureBlocking(false);
}
void close() {
closed = true;
}
boolean isOpen() {
return !closed && channel.isOpen();
}
SelectableChannel getChannel() {
return channel;
}
/**
* Utility function to check if channel is ok.
* Mainly to throw IOException instead of runtime exception
* in case of mismatch. This mismatch can occur for many runtime
* reasons.
*/
static void checkChannelValidity(Object channel) throws IOException {
if (channel == null) {
/* Most common reason is that original socket does not have a channel.
* So making this an IOException rather than a RuntimeException.
*/
throw new IOException("Channel is null. Check " +
"how the channel or socket is created.");
}
if (!(channel instanceof SelectableChannel)) {
throw new IOException("Channel should be a SelectableChannel");
}
}
/**
* Performs actual IO operations. This is not expected to block.
*
* @param buf
* @return number of bytes (or some equivalent). 0 implies underlying
* channel is drained completely. We will wait if more IO is
* required.
* @throws IOException
*/
abstract int performIO(ByteBuffer buf) throws IOException;
/**
* Performs one IO and returns number of bytes read or written.
* It waits up to the specified timeout. If the channel is
* not read before the timeout, SocketTimeoutException is thrown.
*
* @param buf buffer for IO
* @param ops Selection Ops used for waiting. Suggested values:
* SelectionKey.OP_READ while reading and SelectionKey.OP_WRITE while
* writing.
*
* @return number of bytes read or written. negative implies end of stream.
* @throws IOException
*/
int doIO(ByteBuffer buf, int ops) throws IOException {
/* For now only one thread is allowed. If user want to read or write
* from multiple threads, multiple streams could be created. In that
* case multiple threads work as well as underlying channel supports it.
*/
if (!buf.hasRemaining()) {
throw new IllegalArgumentException("Buffer has no data left.");
//or should we just return 0?
}
while (buf.hasRemaining()) {
if (closed) {
return -1;
}
try {
int n = performIO(buf);
if (n != 0) {
// successful io or an error.
return n;
}
} catch (IOException e) {
if (!channel.isOpen()) {
closed = true;
}
throw e;
}
//now wait for socket to be ready.
int count = 0;
try {
count = selector.select(channel, ops, timeout);
} catch (IOException e) { //unexpected IOException.
closed = true;
throw e;
}
if (count == 0) {
throw new SocketTimeoutException(timeoutExceptionString(channel,
timeout, ops));
}
// otherwise the socket should be ready for io.
}
return 0; // does not reach here.
}
/**
* The contract is similar to {@link SocketChannel#connect(SocketAddress)}
* with a timeout.
*
* @see SocketChannel#connect(SocketAddress)
*
* @param channel - this should be a {@link SelectableChannel}
* @param endpoint
* @throws IOException
*/
static void connect(SocketChannel channel,
SocketAddress endpoint, int timeout) throws IOException {
boolean blockingOn = channel.isBlocking();
if (blockingOn) {
channel.configureBlocking(false);
}
try {
if (channel.connect(endpoint)) {
return;
}
long timeoutLeft = timeout;
long endTime = (timeout > 0) ? (System.currentTimeMillis() + timeout): 0;
while (true) {
// we might have to call finishConnect() more than once
// for some channels (with user level protocols)
int ret = selector.select((SelectableChannel)channel,
SelectionKey.OP_CONNECT, timeoutLeft);
if (ret > 0 && channel.finishConnect()) {
return;
}
if (ret == 0 ||
(timeout > 0 &&
(timeoutLeft = (endTime - System.currentTimeMillis())) <= 0)) {
throw new SocketTimeoutException(
timeoutExceptionString(channel, timeout,
SelectionKey.OP_CONNECT));
}
}
} catch (IOException e) {
// javadoc for SocketChannel.connect() says channel should be closed.
try {
channel.close();
} catch (IOException ignored) {}
throw e;
} finally {
if (blockingOn && channel.isOpen()) {
channel.configureBlocking(true);
}
}
}
/**
* This is similar to {@link #doIO(ByteBuffer, int)} except that it
* does not perform any I/O. It just waits for the channel to be ready
* for I/O as specified in ops.
*
* @param ops Selection Ops used for waiting
*
* @throws SocketTimeoutException
* if select on the channel times out.
* @throws IOException
* if any other I/O error occurs.
*/
void waitForIO(int ops) throws IOException {
if (selector.select(channel, ops, timeout) == 0) {
throw new SocketTimeoutException(timeoutExceptionString(channel, timeout,
ops));
}
}
private static String timeoutExceptionString(SelectableChannel channel,
long timeout, int ops) {
String waitingFor;
switch(ops) {
case SelectionKey.OP_READ :
waitingFor = "read"; break;
case SelectionKey.OP_WRITE :
waitingFor = "write"; break;
case SelectionKey.OP_CONNECT :
waitingFor = "connect"; break;
default :
waitingFor = "" + ops;
}
return timeout + " millis timeout while " +
"waiting for channel to be ready for " +
waitingFor + ". ch : " + channel;
}
/**
* This maintains a pool of selectors. These selectors are closed
* once they are idle (unused) for a few seconds.
*/
private static class SelectorPool {
private static class SelectorInfo {
Selector selector;
long lastActivityTime;
LinkedList queue;
void close() {
if (selector != null) {
try {
selector.close();
} catch (IOException e) {
LOG.warn("Unexpected exception while closing selector : " +
StringUtils.stringifyException(e));
}
}
}
}
private static class ProviderInfo {
SelectorProvider provider;
LinkedList queue; // lifo
ProviderInfo next;
}
private static final long IDLE_TIMEOUT = 10 * 1000; // 10 seconds.
private ProviderInfo providerList = null;
/**
* Waits on the channel with the given timeout using one of the
* cached selectors. It also removes any cached selectors that are
* idle for a few seconds.
*
* @param channel
* @param ops
* @param timeout
* @return
* @throws IOException
*/
int select(SelectableChannel channel, int ops, long timeout)
throws IOException {
SelectorInfo info = get(channel);
SelectionKey key = null;
int ret = 0;
try {
while (true) {
long start = (timeout == 0) ? 0 : System.currentTimeMillis();
key = channel.register(info.selector, ops);
ret = info.selector.select(timeout);
if (ret != 0) {
return ret;
}
/* Sometimes select() returns 0 much before timeout for
* unknown reasons. So select again if required.
*/
if (timeout > 0) {
timeout -= System.currentTimeMillis() - start;
if (timeout <= 0) {
return 0;
}
}
if (Thread.currentThread().isInterrupted()) {
throw new InterruptedIOException("Interruped while waiting for " +
"IO on channel " + channel +
". " + timeout +
" millis timeout left.");
}
}
} finally {
if (key != null) {
key.cancel();
}
//clear the canceled key.
try {
info.selector.selectNow();
} catch (IOException e) {
LOG.info("Unexpected Exception while clearing selector : " +
StringUtils.stringifyException(e));
// don't put the selector back.
info.close();
return ret;
}
release(info);
}
}
/**
* Takes one selector from end of LRU list of free selectors.
* If there are no selectors awailable, it creates a new selector.
* Also invokes trimIdleSelectors().
*
* @param channel
* @return
* @throws IOException
*/
private synchronized SelectorInfo get(SelectableChannel channel)
throws IOException {
SelectorInfo selInfo = null;
SelectorProvider provider = channel.provider();
// pick the list : rarely there is more than one provider in use.
ProviderInfo pList = providerList;
while (pList != null && pList.provider != provider) {
pList = pList.next;
}
if (pList == null) {
//LOG.info("Creating new ProviderInfo : " + provider.toString());
pList = new ProviderInfo();
pList.provider = provider;
pList.queue = new LinkedList();
pList.next = providerList;
providerList = pList;
}
LinkedList queue = pList.queue;
if (queue.isEmpty()) {
Selector selector = provider.openSelector();
selInfo = new SelectorInfo();
selInfo.selector = selector;
selInfo.queue = queue;
} else {
selInfo = queue.removeLast();
}
trimIdleSelectors(System.currentTimeMillis());
return selInfo;
}
/**
* puts selector back at the end of LRU list of free selectos.
* Also invokes trimIdleSelectors().
*
* @param info
*/
private synchronized void release(SelectorInfo info) {
long now = System.currentTimeMillis();
trimIdleSelectors(now);
info.lastActivityTime = now;
info.queue.addLast(info);
}
/**
* Closes selectors that are idle for IDLE_TIMEOUT (10 sec). It does not
* traverse the whole list, just over the one that have crossed
* the timeout.
*/
private void trimIdleSelectors(long now) {
long cutoff = now - IDLE_TIMEOUT;
for(ProviderInfo pList=providerList; pList != null; pList=pList.next) {
if (pList.queue.isEmpty()) {
continue;
}
for(Iterator it = pList.queue.iterator(); it.hasNext();) {
SelectorInfo info = it.next();
if (info.lastActivityTime > cutoff) {
break;
}
it.remove();
info.close();
}
}
}
}
}
