tomcat的keepAlive参数深入探究

/**
     * Max keep alive requests
     */
    private int maxKeepAliveRequests=100; // as in Apache HTTPD server
    public int getMaxKeepAliveRequests() {
        // Disable keep-alive if the server socket is not bound
        if (bindState.isBound()) {
            return maxKeepAliveRequests;
        } else {
            return 1;
        }
    }
    public void setMaxKeepAliveRequests(int maxKeepAliveRequests) {
        this.maxKeepAliveRequests = maxKeepAliveRequests;
    }

public class Http11Processor extends AbstractProcessor {
    private static final Log log = LogFactory.getLog(Http11Processor.class);
    public SocketState service(SocketWrapperBase<?> socketWrapper)
        throws IOException {
        RequestInfo rp = request.getRequestProcessor();
        rp.setStage(org.apache.coyote.Constants.STAGE_PARSE);
        // Setting up the I/O
        setSocketWrapper(socketWrapper);
        // Flags
        keepAlive = true;
        openSocket = false;
        readComplete = true;
        boolean keptAlive = false;
        SendfileState sendfileState = SendfileState.DONE;
        //......
        while (!getErrorState().isError() && keepAlive && !isAsync() && upgradeToken == null &&
                sendfileState == SendfileState.DONE && !protocol.isPaused()) {
            //......
            int maxKeepAliveRequests = protocol.getMaxKeepAliveRequests();
            if (maxKeepAliveRequests == 1) {
                keepAlive = false;
            } else if (maxKeepAliveRequests > 0 &&
                    socketWrapper.decrementKeepAlive() <= 0) {
                keepAlive = false;
            }   
            //......
            rp.setStage(org.apache.coyote.Constants.STAGE_KEEPALIVE);
            sendfileState = processSendfile(socketWrapper);            
        }         
    }        
}

public abstract class SocketWrapperBase<E> {
    private static final Log log = LogFactory.getLog(SocketWrapperBase.class);
    protected static final StringManager sm = StringManager.getManager(SocketWrapperBase.class);
    private E socket;
    private final AbstractEndpoint<E,?> endpoint;
    protected final AtomicBoolean closed = new AtomicBoolean(false);
    // Volatile because I/O and setting the timeout values occurs on a different
    // thread to the thread checking the timeout.
    private volatile long readTimeout = -1;
    private volatile long writeTimeout = -1;
    private volatile int keepAliveLeft = 100;
    //......
    public void setKeepAliveLeft(int keepAliveLeft) { this.keepAliveLeft = keepAliveLeft; }
    public int decrementKeepAlive() { return (--keepAliveLeft); }
}

protected final void prepareResponse() throws IOException {
        boolean entityBody = true;
        contentDelimitation = false;
        OutputFilter[] outputFilters = outputBuffer.getFilters();
        if (http09 == true) {
            // HTTP/0.9
            outputBuffer.addActiveFilter(outputFilters[Constants.IDENTITY_FILTER]);
            outputBuffer.commit();
            return;
        }
        //......
        // If we know that the request is bad this early, add the
        // Connection: close header.
        if (keepAlive && statusDropsConnection(statusCode)) {
            keepAlive = false;
        }
        if (!keepAlive) {
            // Avoid adding the close header twice
            if (!connectionClosePresent) {
                headers.addValue(Constants.CONNECTION).setString(
                        Constants.CLOSE);
            }
        } else if (!getErrorState().isError()) {
            if (!http11) {
                headers.addValue(Constants.CONNECTION).setString(Constants.KEEP_ALIVE_HEADER_VALUE_TOKEN);
            }
            if (protocol.getUseKeepAliveResponseHeader()) {
                boolean connectionKeepAlivePresent =
                    isConnectionToken(request.getMimeHeaders(), Constants.KEEP_ALIVE_HEADER_VALUE_TOKEN);
                if (connectionKeepAlivePresent) {
                    int keepAliveTimeout = protocol.getKeepAliveTimeout();
                    if (keepAliveTimeout > 0) {
                        String value = "timeout=" + keepAliveTimeout / 1000L;
                        headers.setValue(Constants.KEEP_ALIVE_HEADER_NAME).setString(value);
                        if (http11) {
                            // Append if there is already a Connection header,
                            // else create the header
                            MessageBytes connectionHeaderValue = headers.getValue(Constants.CONNECTION);
                            if (connectionHeaderValue == null) {
                                headers.addValue(Constants.CONNECTION).setString(Constants.KEEP_ALIVE_HEADER_VALUE_TOKEN);
                            } else {
                                connectionHeaderValue.setString(
                                        connectionHeaderValue.getString() + ", " + Constants.KEEP_ALIVE_HEADER_VALUE_TOKEN);
                            }
                        }
                    }
                }
            }
        }
        //......        
    }    
    /**
     * Determine if we must drop the connection because of the HTTP status
     * code.  Use the same list of codes as Apache/httpd.
     */
    private static boolean statusDropsConnection(int status) {
        return status == 400 /* SC_BAD_REQUEST */ ||
               status == 408 /* SC_REQUEST_TIMEOUT */ ||
               status == 411 /* SC_LENGTH_REQUIRED */ ||
               status == 413 /* SC_REQUEST_ENTITY_TOO_LARGE */ ||
               status == 414 /* SC_REQUEST_URI_TOO_LONG */ ||
               status == 500 /* SC_INTERNAL_SERVER_ERROR */ ||
               status == 503 /* SC_SERVICE_UNAVAILABLE */ ||
               status == 501 /* SC_NOT_IMPLEMENTED */;
    }

public abstract class AbstractEndpoint<S,U> {
    //......
    /**
     * Keepalive timeout, if not set the soTimeout is used.
     */
    private Integer keepAliveTimeout = null;
    public int getKeepAliveTimeout() {
        if (keepAliveTimeout == null) {
            return getConnectionTimeout();
        } else {
            return keepAliveTimeout.intValue();
        }
    }
    public void setKeepAliveTimeout(int keepAliveTimeout) {
        this.keepAliveTimeout = Integer.valueOf(keepAliveTimeout);
    }
    /**
     * Socket timeout.
     *
     * @return The current socket timeout for sockets created by this endpoint
     */
    public int getConnectionTimeout() { return socketProperties.getSoTimeout(); }
    public void setConnectionTimeout(int soTimeout) { socketProperties.setSoTimeout(soTimeout); }
    //......
}

public SocketState service(SocketWrapperBase<?> socketWrapper)
        throws IOException {
        RequestInfo rp = request.getRequestProcessor();
        rp.setStage(org.apache.coyote.Constants.STAGE_PARSE);

        // Setting up the I/O
        setSocketWrapper(socketWrapper);

        // Flags
        keepAlive = true;
        openSocket = false;
        readComplete = true;
        boolean keptAlive = false;
        SendfileState sendfileState = SendfileState.DONE;

        while (!getErrorState().isError() && keepAlive && !isAsync() && upgradeToken == null &&
                sendfileState == SendfileState.DONE && !protocol.isPaused()) {

            // Parsing the request header
            try {
                if (!inputBuffer.parseRequestLine(keptAlive, protocol.getConnectionTimeout(),
                        protocol.getKeepAliveTimeout())) {
                    if (inputBuffer.getParsingRequestLinePhase() == -1) {
                        return SocketState.UPGRADING;
                    } else if (handleIncompleteRequestLineRead()) {
                        break;
                    }
                }
            }
            
            //......
        }
    }

    /**
     * Read the request line. This function is meant to be used during the
     * HTTP request header parsing. Do NOT attempt to read the request body
     * using it.
     *
     * @throws IOException If an exception occurs during the underlying socket
     * read operations, or if the given buffer is not big enough to accommodate
     * the whole line.
     *
     * @return true if data is properly fed; false if no data is available
     * immediately and thread should be freed
     */
    boolean parseRequestLine(boolean keptAlive, int connectionTimeout, int keepAliveTimeout)
            throws IOException {
        // check state
        if (!parsingRequestLine) {
            return true;
        }
        //
        // Skipping blank lines
        //
        if (parsingRequestLinePhase < 2) {
            do {
                // Read new bytes if needed
                if (byteBuffer.position() >= byteBuffer.limit()) {
                    if (keptAlive) {
                        // Haven't read any request data yet so use the keep-alive
                        // timeout.
                        wrapper.setReadTimeout(keepAliveTimeout);
                    }
                    if (!fill(false)) {
                        // A read is pending, so no longer in initial state
                        parsingRequestLinePhase = 1;
                        return false;
                    }
                    // At least one byte of the request has been received.
                    // Switch to the socket timeout.
                    wrapper.setReadTimeout(connectionTimeout);
                }
                if (!keptAlive && byteBuffer.position() == 0 && byteBuffer.limit() >= CLIENT_PREFACE_START.length - 1) {
                    boolean prefaceMatch = true;
                    for (int i = 0; i < CLIENT_PREFACE_START.length && prefaceMatch; i++) {
                        if (CLIENT_PREFACE_START[i] != byteBuffer.get(i)) {
                            prefaceMatch = false;
                        }
                    }
                    if (prefaceMatch) {
                        // HTTP/2 preface matched
                        parsingRequestLinePhase = -1;
                        return false;
                    }
                }
                // Set the start time once we start reading data (even if it is
                // just skipping blank lines)
                if (request.getStartTime() < 0) {
                    request.setStartTime(System.currentTimeMillis());
                }
                chr = byteBuffer.get();
            } while ((chr == Constants.CR) || (chr == Constants.LF));
            byteBuffer.position(byteBuffer.position() - 1);
            parsingRequestLineStart = byteBuffer.position();
            parsingRequestLinePhase = 2;
        }
        if (parsingRequestLinePhase == 2) {
            //
            // Reading the method name
            // Method name is a token
            //
            boolean space = false;
            while (!space) {
                // Read new bytes if needed
                if (byteBuffer.position() >= byteBuffer.limit()) {
                    if (!fill(false)) // request line parsing
                        return false;
                }
                // Spec says method name is a token followed by a single SP but
                // also be tolerant of multiple SP and/or HT.
                int pos = byteBuffer.position();
                chr = byteBuffer.get();
                if (chr == Constants.SP || chr == Constants.HT) {
                    space = true;
                    request.method().setBytes(byteBuffer.array(), parsingRequestLineStart,
                            pos - parsingRequestLineStart);
                } else if (!HttpParser.isToken(chr)) {
                    // Avoid unknown protocol triggering an additional error
                    request.protocol().setString(Constants.HTTP_11);
                    String invalidMethodValue = parseInvalid(parsingRequestLineStart, byteBuffer);
                    throw new IllegalArgumentException(sm.getString("iib.invalidmethod", invalidMethodValue));
                }
            }
            parsingRequestLinePhase = 3;
        }
        if (parsingRequestLinePhase == 3) {
            // Spec says single SP but also be tolerant of multiple SP and/or HT
            boolean space = true;
            while (space) {
                // Read new bytes if needed
                if (byteBuffer.position() >= byteBuffer.limit()) {
                    if (!fill(false)) // request line parsing
                        return false;
                }
                chr = byteBuffer.get();
                if (!(chr == Constants.SP || chr == Constants.HT)) {
                    space = false;
                    byteBuffer.position(byteBuffer.position() - 1);
                }
            }
            parsingRequestLineStart = byteBuffer.position();
            parsingRequestLinePhase = 4;
        }
        if (parsingRequestLinePhase == 4) {
            // Mark the current buffer position
            int end = 0;
            //
            // Reading the URI
            //
            boolean space = false;
            while (!space) {
                // Read new bytes if needed
                if (byteBuffer.position() >= byteBuffer.limit()) {
                    if (!fill(false)) // request line parsing
                        return false;
                }
                int pos = byteBuffer.position();
                prevChr = chr;
                chr = byteBuffer.get();
                if (prevChr == Constants.CR && chr != Constants.LF) {
                    // CR not followed by LF so not an HTTP/0.9 request and
                    // therefore invalid. Trigger error handling.
                    // Avoid unknown protocol triggering an additional error
                    request.protocol().setString(Constants.HTTP_11);
                    String invalidRequestTarget = parseInvalid(parsingRequestLineStart, byteBuffer);
                    throw new IllegalArgumentException(sm.getString("iib.invalidRequestTarget", invalidRequestTarget));
                }
                if (chr == Constants.SP || chr == Constants.HT) {
                    space = true;
                    end = pos;
                } else if (chr == Constants.CR) {
                    // HTTP/0.9 style request. CR is optional. LF is not.
                } else if (chr == Constants.LF) {
                    // HTTP/0.9 style request
                    // Stop this processing loop
                    space = true;
                    // Set blank protocol (indicates HTTP/0.9)
                    request.protocol().setString("");
                    // Skip the protocol processing
                    parsingRequestLinePhase = 7;
                    if (prevChr == Constants.CR) {
                        end = pos - 1;
                    } else {
                        end = pos;
                    }
                } else if (chr == Constants.QUESTION && parsingRequestLineQPos == -1) {
                    parsingRequestLineQPos = pos;
                } else if (parsingRequestLineQPos != -1 && !httpParser.isQueryRelaxed(chr)) {
                    // Avoid unknown protocol triggering an additional error
                    request.protocol().setString(Constants.HTTP_11);
                    // %nn decoding will be checked at the point of decoding
                    String invalidRequestTarget = parseInvalid(parsingRequestLineStart, byteBuffer);
                    throw new IllegalArgumentException(sm.getString("iib.invalidRequestTarget", invalidRequestTarget));
                } else if (httpParser.isNotRequestTargetRelaxed(chr)) {
                    // Avoid unknown protocol triggering an additional error
                    request.protocol().setString(Constants.HTTP_11);
                    // This is a general check that aims to catch problems early
                    // Detailed checking of each part of the request target will
                    // happen in Http11Processor#prepareRequest()
                    String invalidRequestTarget = parseInvalid(parsingRequestLineStart, byteBuffer);
                    throw new IllegalArgumentException(sm.getString("iib.invalidRequestTarget", invalidRequestTarget));
                }
            }
            if (parsingRequestLineQPos >= 0) {
                request.queryString().setBytes(byteBuffer.array(), parsingRequestLineQPos + 1,
                        end - parsingRequestLineQPos - 1);
                request.requestURI().setBytes(byteBuffer.array(), parsingRequestLineStart,
                        parsingRequestLineQPos - parsingRequestLineStart);
            } else {
                request.requestURI().setBytes(byteBuffer.array(), parsingRequestLineStart,
                        end - parsingRequestLineStart);
            }
            // HTTP/0.9 processing jumps to stage 7.
            // Don't want to overwrite that here.
            if (parsingRequestLinePhase == 4) {
                parsingRequestLinePhase = 5;
            }
        }
        if (parsingRequestLinePhase == 5) {
            // Spec says single SP but also be tolerant of multiple and/or HT
            boolean space = true;
            while (space) {
                // Read new bytes if needed
                if (byteBuffer.position() >= byteBuffer.limit()) {
                    if (!fill(false)) // request line parsing
                        return false;
                }
                byte chr = byteBuffer.get();
                if (!(chr == Constants.SP || chr == Constants.HT)) {
                    space = false;
                    byteBuffer.position(byteBuffer.position() - 1);
                }
            }
            parsingRequestLineStart = byteBuffer.position();
            parsingRequestLinePhase = 6;
            // Mark the current buffer position
            end = 0;
        }
        if (parsingRequestLinePhase == 6) {
            //
            // Reading the protocol
            // Protocol is always "HTTP/" DIGIT "." DIGIT
            //
            while (!parsingRequestLineEol) {
                // Read new bytes if needed
                if (byteBuffer.position() >= byteBuffer.limit()) {
                    if (!fill(false)) // request line parsing
                        return false;
                }
                int pos = byteBuffer.position();
                prevChr = chr;
                chr = byteBuffer.get();
                if (chr == Constants.CR) {
                    // Possible end of request line. Need LF next.
                } else if (prevChr == Constants.CR && chr == Constants.LF) {
                    end = pos - 1;
                    parsingRequestLineEol = true;
                } else if (!HttpParser.isHttpProtocol(chr)) {
                    String invalidProtocol = parseInvalid(parsingRequestLineStart, byteBuffer);
                    throw new IllegalArgumentException(sm.getString("iib.invalidHttpProtocol", invalidProtocol));
                }
            }
            if ((end - parsingRequestLineStart) > 0) {
                request.protocol().setBytes(byteBuffer.array(), parsingRequestLineStart,
                        end - parsingRequestLineStart);
                parsingRequestLinePhase = 7;
            }
            // If no protocol is found, the ISE below will be triggered.
        }
        if (parsingRequestLinePhase == 7) {
            // Parsing is complete. Return and clean-up.
            parsingRequestLine = false;
            parsingRequestLinePhase = 0;
            parsingRequestLineEol = false;
            parsingRequestLineStart = 0;
            return true;
        }
        throw new IllegalStateException(sm.getString("iib.invalidPhase", Integer.valueOf(parsingRequestLinePhase)));
    }