Tomcat example source code file (NioSelectorPool.java)

This example Tomcat source code file (NioSelectorPool.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Tomcat tags/keywords

atomicinteger, concurrentlinkedqueue, eofexception, io, ioexception, ioexception, net, network, nio, niochannel, nioselectorpool, selectionkey, selector, selector, shared, shared, shared_selector, shared_selector, threading, threads

The Tomcat NioSelectorPool.java source code

/*
 * 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.tomcat.util.net;

import java.io.EOFException;
import java.io.IOException;
import java.net.SocketTimeoutException;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.util.NoSuchElementException;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.atomic.AtomicInteger;

import org.apache.juli.logging.Log;
import org.apache.juli.logging.LogFactory;
import org.apache.tomcat.util.MutableInteger;

/**
 *
 * Thread safe non blocking selector pool
 * @author Filip Hanik
 * @version 1.0
 * @since 6.0
 */

public class NioSelectorPool {
    
    public NioSelectorPool() {
    }
    
    protected static int threadCount = 0;
    
    protected static Log log = LogFactory.getLog(NioSelectorPool.class);

    protected final static boolean SHARED =
        Boolean.valueOf(System.getProperty("org.apache.tomcat.util.net.NioSelectorShared", "true")).booleanValue();
    
    protected NioBlockingSelector blockingSelector;
    
    protected Selector SHARED_SELECTOR;
    
    protected int maxSelectors = 200;
    protected long sharedSelectorTimeout = 30000;
    protected int maxSpareSelectors = -1;
    protected boolean enabled = true;
    protected AtomicInteger active = new AtomicInteger(0);
    protected AtomicInteger spare = new AtomicInteger(0);
    protected ConcurrentLinkedQueue<Selector> selectors = new ConcurrentLinkedQueue();

    protected Selector getSharedSelector() throws IOException {
        if (SHARED && SHARED_SELECTOR == null) {
            synchronized ( NioSelectorPool.class ) {
                if ( SHARED_SELECTOR == null )  {
                    SHARED_SELECTOR = Selector.open();
                    log.info("Using a shared selector for servlet write/read");
                }
            }
        }
        return  SHARED_SELECTOR;
    }

    public Selector get() throws IOException{
        if ( SHARED ) {
            return getSharedSelector();
        }
        if ( (!enabled) || active.incrementAndGet() >= maxSelectors ) {
            if ( enabled ) active.decrementAndGet();
            return null;
        }
        Selector s = null;
        try {
            s = selectors.size()>0?selectors.poll():null;
            if (s == null) s = Selector.open();
            else spare.decrementAndGet();

        }catch (NoSuchElementException x ) {
            try {s = Selector.open();}catch (IOException iox){}
        } finally {
            if ( s == null ) active.decrementAndGet();//we were unable to find a selector
        }
        return s;
    }



    public void put(Selector s) throws IOException {
        if ( SHARED ) return;
        if ( enabled ) active.decrementAndGet();
        if ( enabled && (maxSpareSelectors==-1 || spare.get() < Math.min(maxSpareSelectors,maxSelectors)) ) {
            spare.incrementAndGet();
            selectors.offer(s);
        }
        else s.close();
    }

    public void close() throws IOException {
        enabled = false;
        Selector s;
        while ( (s = selectors.poll()) != null ) s.close();
        spare.set(0);
        active.set(0);
        if (blockingSelector!=null) {
            blockingSelector.close();
        }
        if ( SHARED && getSharedSelector()!=null ) {
            getSharedSelector().close();
            SHARED_SELECTOR = null;
        }
    }

    public void open() throws IOException {
        enabled = true;
        getSharedSelector();
        if (SHARED) {
            blockingSelector = new NioBlockingSelector();
            blockingSelector.open(getSharedSelector());
        }

    }

    /**
     * Performs a blocking write using the bytebuffer for data to be written and a selector to block.
     * If the <code>selector parameter is null, then it will perform a busy write that could
     * take up a lot of CPU cycles.
     * @param buf ByteBuffer - the buffer containing the data, we will write as long as <code>(buf.hasRemaining()==true)
     * @param socket SocketChannel - the socket to write data to
     * @param selector Selector - the selector to use for blocking, if null then a busy write will be initiated
     * @param writeTimeout long - the timeout for this write operation in milliseconds, -1 means no timeout
     * @return int - returns the number of bytes written
     * @throws EOFException if write returns -1
     * @throws SocketTimeoutException if the write times out
     * @throws IOException if an IO Exception occurs in the underlying socket logic
     */
    public int write(ByteBuffer buf, NioChannel socket, Selector selector, long writeTimeout) throws IOException {
        return write(buf,socket,selector,writeTimeout,true,null);
    }
    
    public int write(ByteBuffer buf, NioChannel socket, Selector selector, 
                     long writeTimeout, boolean block,MutableInteger lastWrite) throws IOException {
        if ( SHARED && block ) {
            return blockingSelector.write(buf,socket,writeTimeout,lastWrite);
        }
        SelectionKey key = null;
        int written = 0;
        boolean timedout = false;
        int keycount = 1; //assume we can write
        long time = System.currentTimeMillis(); //start the timeout timer
        try {
            while ( (!timedout) && buf.hasRemaining() ) {
                int cnt = 0;
                if ( keycount > 0 ) { //only write if we were registered for a write
                    cnt = socket.write(buf); //write the data
                    if (lastWrite!=null) lastWrite.set(cnt);
                    if (cnt == -1) throw new EOFException();
                    
                    written += cnt;
                    if (cnt > 0) {
                        time = System.currentTimeMillis(); //reset our timeout timer
                        continue; //we successfully wrote, try again without a selector
                    }
                    if (cnt==0 && (!block)) break; //don't block
                }
                if ( selector != null ) {
                    //register OP_WRITE to the selector
                    if (key==null) key = socket.getIOChannel().register(selector, SelectionKey.OP_WRITE);
                    else key.interestOps(SelectionKey.OP_WRITE);
                    keycount = selector.select(writeTimeout);
                }
                if (writeTimeout > 0 && (selector == null || keycount == 0) ) timedout = (System.currentTimeMillis()-time)>=writeTimeout;
            }//while
            if ( timedout ) throw new SocketTimeoutException();
        } finally {
            if (key != null) {
                key.cancel();
                if (selector != null) selector.selectNow();//removes the key from this selector
            }
        }
        return written;
    }

    /**
     * Performs a blocking read using the bytebuffer for data to be read and a selector to block.
     * If the <code>selector parameter is null, then it will perform a busy read that could
     * take up a lot of CPU cycles.
     * @param buf ByteBuffer - the buffer containing the data, we will read as until we have read at least one byte or we timed out
     * @param socket SocketChannel - the socket to write data to
     * @param selector Selector - the selector to use for blocking, if null then a busy read will be initiated
     * @param readTimeout long - the timeout for this read operation in milliseconds, -1 means no timeout
     * @return int - returns the number of bytes read
     * @throws EOFException if read returns -1
     * @throws SocketTimeoutException if the read times out
     * @throws IOException if an IO Exception occurs in the underlying socket logic
     */
    public int read(ByteBuffer buf, NioChannel socket, Selector selector, long readTimeout) throws IOException {
        return read(buf,socket,selector,readTimeout,true);
    }
    /**
     * Performs a read using the bytebuffer for data to be read and a selector to register for events should 
     * you have the block=true.
     * If the <code>selector parameter is null, then it will perform a busy read that could
     * take up a lot of CPU cycles.
     * @param buf ByteBuffer - the buffer containing the data, we will read as until we have read at least one byte or we timed out
     * @param socket SocketChannel - the socket to write data to
     * @param selector Selector - the selector to use for blocking, if null then a busy read will be initiated
     * @param readTimeout long - the timeout for this read operation in milliseconds, -1 means no timeout
     * @param block - true if you want to block until data becomes available or timeout time has been reached
     * @return int - returns the number of bytes read
     * @throws EOFException if read returns -1
     * @throws SocketTimeoutException if the read times out
     * @throws IOException if an IO Exception occurs in the underlying socket logic
     */
    public int read(ByteBuffer buf, NioChannel socket, Selector selector, long readTimeout, boolean block) throws IOException {
        if ( SHARED && block ) {
            return blockingSelector.read(buf,socket,readTimeout);
        }
        SelectionKey key = null;
        int read = 0;
        boolean timedout = false;
        int keycount = 1; //assume we can write
        long time = System.currentTimeMillis(); //start the timeout timer
        try {
            while ( (!timedout) ) {
                int cnt = 0;
                if ( keycount > 0 ) { //only read if we were registered for a read
                    cnt = socket.read(buf);
                    if (cnt == -1) throw new EOFException();
                    read += cnt;
                    if (cnt > 0) continue; //read some more
                    if (cnt==0 && (read>0 || (!block) ) ) break; //we are done reading
                } 
                if ( selector != null ) {//perform a blocking read
                    //register OP_WRITE to the selector
                    if (key==null) key = socket.getIOChannel().register(selector, SelectionKey.OP_READ);
                    else key.interestOps(SelectionKey.OP_READ);
                    keycount = selector.select(readTimeout);
                }
                if (readTimeout > 0 && (selector == null || keycount == 0) ) timedout = (System.currentTimeMillis()-time)>=readTimeout;
            }//while
            if ( timedout ) throw new SocketTimeoutException();
        } finally {
            if (key != null) {
                key.cancel();
                if (selector != null) selector.selectNow();//removes the key from this selector
            }
        }
        return read;
    }

    public void setMaxSelectors(int maxSelectors) {
        this.maxSelectors = maxSelectors;
    }

    public void setMaxSpareSelectors(int maxSpareSelectors) {
        this.maxSpareSelectors = maxSpareSelectors;
    }

    public void setEnabled(boolean enabled) {
        this.enabled = enabled;
    }

    public void setSharedSelectorTimeout(long sharedSelectorTimeout) {
        this.sharedSelectorTimeout = sharedSelectorTimeout;
    }

    public int getMaxSelectors() {
        return maxSelectors;
    }

    public int getMaxSpareSelectors() {
        return maxSpareSelectors;
    }

    public boolean isEnabled() {
        return enabled;
    }

    public long getSharedSelectorTimeout() {
        return sharedSelectorTimeout;
    }

    public ConcurrentLinkedQueue getSelectors() {
        return selectors;
    }

    public AtomicInteger getSpare() {
        return spare;
    }
}