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聊聊netty的ResourceLeakDetector

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本文主要研究一下netty的ResourceLeakDetector

LEAK异常

2019-04-02 15:23:17.026 ERROR 1 --- [reactor-http-epoll-2] io.netty.util.ResourceLeakDetector       : LEAK: ByteBuf.release() was not called before it's garbage-collected. See http://netty.io/wiki/reference-counted-objects.html for more information.
Recent access records: 
#1:
    io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:286)
    io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:253)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
    io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340)
    io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1408)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
    io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:930)
    io.netty.channel.epoll.AbstractEpollStreamChannel$EpollStreamUnsafe.epollInReady(AbstractEpollStreamChannel.java:799)
    io.netty.channel.epoll.EpollEventLoop.processReady(EpollEventLoop.java:427)
    io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:328)
    io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:905)
    java.base/java.lang.Thread.run(Thread.java:835)
#2:
    io.netty.buffer.AdvancedLeakAwareByteBuf.forEachByte(AdvancedLeakAwareByteBuf.java:670)
    io.netty.handler.codec.http.HttpObjectDecoder$HeaderParser.parse(HttpObjectDecoder.java:801)
    io.netty.handler.codec.http.HttpObjectDecoder.readHeaders(HttpObjectDecoder.java:601)
    io.netty.handler.codec.http.HttpObjectDecoder.decode(HttpObjectDecoder.java:227)
    io.netty.handler.codec.http.HttpClientCodec$Decoder.decode(HttpClientCodec.java:202)
    io.netty.handler.codec.ByteToMessageDecoder.decodeRemovalReentryProtection(ByteToMessageDecoder.java:502)
    io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:441)
    io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:278)
    io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:253)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
    io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340)
    io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1408)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
    io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:930)
    io.netty.channel.epoll.AbstractEpollStreamChannel$EpollStreamUnsafe.epollInReady(AbstractEpollStreamChannel.java:799)
    io.netty.channel.epoll.EpollEventLoop.processReady(EpollEventLoop.java:427)
    io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:328)
    io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:905)
    java.base/java.lang.Thread.run(Thread.java:835)
#3:
    io.netty.buffer.AdvancedLeakAwareByteBuf.forEachByte(AdvancedLeakAwareByteBuf.java:670)
    io.netty.handler.codec.http.HttpObjectDecoder$HeaderParser.parse(HttpObjectDecoder.java:801)
    io.netty.handler.codec.http.HttpObjectDecoder.readHeaders(HttpObjectDecoder.java:581)
    io.netty.handler.codec.http.HttpObjectDecoder.decode(HttpObjectDecoder.java:227)
    io.netty.handler.codec.http.HttpClientCodec$Decoder.decode(HttpClientCodec.java:202)
    io.netty.handler.codec.ByteToMessageDecoder.decodeRemovalReentryProtection(ByteToMessageDecoder.java:502)
    io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:441)
    io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:278)
    io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:253)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
    io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340)
    io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1408)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
    io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:930)
    io.netty.channel.epoll.AbstractEpollStreamChannel$EpollStreamUnsafe.epollInReady(AbstractEpollStreamChannel.java:799)
    io.netty.channel.epoll.EpollEventLoop.processReady(EpollEventLoop.java:427)
    io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:328)
    io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:905)
    java.base/java.lang.Thread.run(Thread.java:835)
#4:
    io.netty.buffer.AdvancedLeakAwareByteBuf.forEachByte(AdvancedLeakAwareByteBuf.java:670)
    io.netty.handler.codec.http.HttpObjectDecoder$HeaderParser.parse(HttpObjectDecoder.java:801)
    io.netty.handler.codec.http.HttpObjectDecoder$LineParser.parse(HttpObjectDecoder.java:850)
    io.netty.handler.codec.http.HttpObjectDecoder.decode(HttpObjectDecoder.java:208)
    io.netty.handler.codec.http.HttpClientCodec$Decoder.decode(HttpClientCodec.java:202)
    io.netty.handler.codec.ByteToMessageDecoder.decodeRemovalReentryProtection(ByteToMessageDecoder.java:502)
    io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:441)
    io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:278)
    io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:253)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
    io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340)
    io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1408)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
    io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:930)
    io.netty.channel.epoll.AbstractEpollStreamChannel$EpollStreamUnsafe.epollInReady(AbstractEpollStreamChannel.java:799)
    io.netty.channel.epoll.EpollEventLoop.processReady(EpollEventLoop.java:427)
    io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:328)
    io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:905)
    java.base/java.lang.Thread.run(Thread.java:835)
#5:
    io.netty.buffer.AdvancedLeakAwareByteBuf.getUnsignedByte(AdvancedLeakAwareByteBuf.java:160)
    io.netty.handler.codec.http.HttpObjectDecoder.skipControlCharacters(HttpObjectDecoder.java:566)
    io.netty.handler.codec.http.HttpObjectDecoder.decode(HttpObjectDecoder.java:202)
    io.netty.handler.codec.http.HttpClientCodec$Decoder.decode(HttpClientCodec.java:202)
    io.netty.handler.codec.ByteToMessageDecoder.decodeRemovalReentryProtection(ByteToMessageDecoder.java:502)
    io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:441)
    io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:278)
    io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:253)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
    io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340)
    io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1408)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
    io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:930)
    io.netty.channel.epoll.AbstractEpollStreamChannel$EpollStreamUnsafe.epollInReady(AbstractEpollStreamChannel.java:799)
    io.netty.channel.epoll.EpollEventLoop.processReady(EpollEventLoop.java:427)
    io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:328)
    io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:905)
    java.base/java.lang.Thread.run(Thread.java:835)
#6:
    Hint: 'reactor.left.httpCodec' will handle the message from this point.
    io.netty.channel.DefaultChannelPipeline.touch(DefaultChannelPipeline.java:116)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:345)
    io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340)
    io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1408)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
    io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:930)
    io.netty.channel.epoll.AbstractEpollStreamChannel$EpollStreamUnsafe.epollInReady(AbstractEpollStreamChannel.java:799)
    io.netty.channel.epoll.EpollEventLoop.processReady(EpollEventLoop.java:427)
    io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:328)
    io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:905)
    java.base/java.lang.Thread.run(Thread.java:835)
#7:
    Hint: 'DefaultChannelPipeline$HeadContext#0' will handle the message from this point.
    io.netty.channel.DefaultChannelPipeline.touch(DefaultChannelPipeline.java:116)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:345)
    io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:930)
    io.netty.channel.epoll.AbstractEpollStreamChannel$EpollStreamUnsafe.epollInReady(AbstractEpollStreamChannel.java:799)
    io.netty.channel.epoll.EpollEventLoop.processReady(EpollEventLoop.java:427)
    io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:328)
    io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:905)
    java.base/java.lang.Thread.run(Thread.java:835)
Created at:
    io.netty.buffer.PooledByteBufAllocator.newDirectBuffer(PooledByteBufAllocator.java:339)
    io.netty.buffer.AbstractByteBufAllocator.directBuffer(AbstractByteBufAllocator.java:185)
    io.netty.buffer.AbstractByteBufAllocator.directBuffer(AbstractByteBufAllocator.java:176)
    io.netty.channel.unix.PreferredDirectByteBufAllocator.ioBuffer(PreferredDirectByteBufAllocator.java:53)
    io.netty.channel.DefaultMaxMessagesRecvByteBufAllocator$MaxMessageHandle.allocate(DefaultMaxMessagesRecvByteBufAllocator.java:114)
    io.netty.channel.epoll.EpollRecvByteAllocatorHandle.allocate(EpollRecvByteAllocatorHandle.java:77)
    io.netty.channel.epoll.AbstractEpollStreamChannel$EpollStreamUnsafe.epollInReady(AbstractEpollStreamChannel.java:784)
    io.netty.channel.epoll.EpollEventLoop.processReady(EpollEventLoop.java:427)
    io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:328)
    io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:905)
    java.base/java.lang.Thread.run(Thread.java:835)
: 9 leak records were discarded because the leak record count is targeted to 4. Use system property io.netty.leakDetection.targetRecords to increase the limit.

ResourceLeakDetector

netty-common-4.1.33.Final-sources.jar!/io/netty/util/ResourceLeakDetector.java

public class ResourceLeakDetector {

    private static final String PROP_LEVEL_OLD = "io.netty.leakDetectionLevel";
    private static final String PROP_LEVEL = "io.netty.leakDetection.level";
    private static final Level DEFAULT_LEVEL = Level.SIMPLE;

    private static final String PROP_TARGET_RECORDS = "io.netty.leakDetection.targetRecords";
    private static final int DEFAULT_TARGET_RECORDS = 4;

    private static final String PROP_SAMPLING_INTERVAL = "io.netty.leakDetection.samplingInterval";
    // There is a minor performance benefit in TLR if this is a power of 2.
    private static final int DEFAULT_SAMPLING_INTERVAL = 128;

    private static final int TARGET_RECORDS;
    static final int SAMPLING_INTERVAL;

    /**
     * Represents the level of resource leak detection.
     */
    public enum Level {
        /**
         * Disables resource leak detection.
         */
        DISABLED,
        /**
         * Enables simplistic sampling resource leak detection which reports there is a leak or not,
         * at the cost of small overhead (default).
         */
        SIMPLE,
        /**
         * Enables advanced sampling resource leak detection which reports where the leaked object was accessed
         * recently at the cost of high overhead.
         */
        ADVANCED,
        /**
         * Enables paranoid resource leak detection which reports where the leaked object was accessed recently,
         * at the cost of the highest possible overhead (for testing purposes only).
         */
        PARANOID;

        /**
         * Returns level based on string value. Accepts also string that represents ordinal number of enum.
         *
         * @param levelStr - level string : DISABLED, SIMPLE, ADVANCED, PARANOID. Ignores case.
         * @return corresponding level or SIMPLE level in case of no match.
         */
        static Level parseLevel(String levelStr) {
            String trimmedLevelStr = levelStr.trim();
            for (Level l : values()) {
                if (trimmedLevelStr.equalsIgnoreCase(l.name()) || trimmedLevelStr.equals(String.valueOf(l.ordinal()))) {
                    return l;
                }
            }
            return DEFAULT_LEVEL;
        }
    }

    private static Level level;

    private static final InternalLogger logger = InternalLoggerFactory.getInstance(ResourceLeakDetector.class);

    static {
        final boolean disabled;
        if (SystemPropertyUtil.get("io.netty.noResourceLeakDetection") != null) {
            disabled = SystemPropertyUtil.getBoolean("io.netty.noResourceLeakDetection", false);
            logger.debug("-Dio.netty.noResourceLeakDetection: {}", disabled);
            logger.warn(
                    "-Dio.netty.noResourceLeakDetection is deprecated. Use '-D{}={}' instead.",
                    PROP_LEVEL, DEFAULT_LEVEL.name().toLowerCase());
        } else {
            disabled = false;
        }

        Level defaultLevel = disabled? Level.DISABLED : DEFAULT_LEVEL;

        // First read old property name
        String levelStr = SystemPropertyUtil.get(PROP_LEVEL_OLD, defaultLevel.name());

        // If new property name is present, use it
        levelStr = SystemPropertyUtil.get(PROP_LEVEL, levelStr);
        Level level = Level.parseLevel(levelStr);

        TARGET_RECORDS = SystemPropertyUtil.getInt(PROP_TARGET_RECORDS, DEFAULT_TARGET_RECORDS);
        SAMPLING_INTERVAL = SystemPropertyUtil.getInt(PROP_SAMPLING_INTERVAL, DEFAULT_SAMPLING_INTERVAL);

        ResourceLeakDetector.level = level;
        if (logger.isDebugEnabled()) {
            logger.debug("-D{}: {}", PROP_LEVEL, level.name().toLowerCase());
            logger.debug("-D{}: {}", PROP_TARGET_RECORDS, TARGET_RECORDS);
        }
    }

    /**
     * @deprecated Use {@link #setLevel(Level)} instead.
     */
    @Deprecated
    public static void setEnabled(boolean enabled) {
        setLevel(enabled? Level.SIMPLE : Level.DISABLED);
    }

    /**
     * Returns {@code true} if resource leak detection is enabled.
     */
    public static boolean isEnabled() {
        return getLevel().ordinal() > Level.DISABLED.ordinal();
    }

    /**
     * Sets the resource leak detection level.
     */
    public static void setLevel(Level level) {
        if (level == null) {
            throw new NullPointerException("level");
        }
        ResourceLeakDetector.level = level;
    }

    /**
     * Returns the current resource leak detection level.
     */
    public static Level getLevel() {
        return level;
    }

    /** the collection of active resources */
    private final Set> allLeaks =
            Collections.newSetFromMap(new ConcurrentHashMap, Boolean>());

    private final ReferenceQueue refQueue = new ReferenceQueue();
    private final ConcurrentMap reportedLeaks = PlatformDependent.newConcurrentHashMap();

    private final String resourceType;
    private final int samplingInterval;

    //......

    /**
     * Creates a new {@link ResourceLeakTracker} which is expected to be closed via
     * {@link ResourceLeakTracker#close(Object)} when the related resource is deallocated.
     *
     * @return the {@link ResourceLeakTracker} or {@code null}
     */
    @SuppressWarnings("unchecked")
    public final ResourceLeakTracker track(T obj) {
        return track0(obj);
    }

    private DefaultResourceLeak track0(T obj) {
        Level level = ResourceLeakDetector.level;
        if (level == Level.DISABLED) {
            return null;
        }

        if (level.ordinal() < Level.PARANOID.ordinal()) {
            if ((PlatformDependent.threadLocalRandom().nextInt(samplingInterval)) == 0) {
                reportLeak();
                return new DefaultResourceLeak(obj, refQueue, allLeaks);
            }
            return null;
        }
        reportLeak();
        return new DefaultResourceLeak(obj, refQueue, allLeaks);
    }

    private void reportLeak() {
        if (!logger.isErrorEnabled()) {
            clearRefQueue();
            return;
        }

        // Detect and report previous leaks.
        for (;;) {
            @SuppressWarnings("unchecked")
            DefaultResourceLeak ref = (DefaultResourceLeak) refQueue.poll();
            if (ref == null) {
                break;
            }

            if (!ref.dispose()) {
                continue;
            }

            String records = ref.toString();
            if (reportedLeaks.putIfAbsent(records, Boolean.TRUE) == null) {
                if (records.isEmpty()) {
                    reportUntracedLeak(resourceType);
                } else {
                    reportTracedLeak(resourceType, records);
                }
            }
        }
    }

    /**
     * This method is called when a traced leak is detected. It can be overridden for tracking how many times leaks
     * have been detected.
     */
    protected void reportTracedLeak(String resourceType, String records) {
        logger.error(
                "LEAK: {}.release() was not called before it's garbage-collected. " +
                "See http://netty.io/wiki/reference-counted-objects.html for more information.{}",
                resourceType, records);
    }

    /**
     * This method is called when an untraced leak is detected. It can be overridden for tracking how many times leaks
     * have been detected.
     */
    protected void reportUntracedLeak(String resourceType) {
        logger.error("LEAK: {}.release() was not called before it's garbage-collected. " +
                "Enable advanced leak reporting to find out where the leak occurred. " +
                "To enable advanced leak reporting, " +
                "specify the JVM option '-D{}={}' or call {}.setLevel() " +
                "See http://netty.io/wiki/reference-counted-objects.html for more information.",
                resourceType, PROP_LEVEL, Level.ADVANCED.name().toLowerCase(), simpleClassName(this));
    }

    //......
} 
 
     
  
  • ResourceLeakDetector使用Level枚举定义了四种不同的leak detection级别，分别是DISABLED、SIMPLE、ADVANCED、PARANOID；默认level为SIMPLE；可以使用-Dio.netty.leakDetection.level=advanced来进行设置
    •  
  
  • ResourceLeakDetector的静态代码块会读取io.netty.noResourceLeakDetection系统属性，如果显示设置为false，则变更defaultLevel为DISABLED；如果没有设置，则默认disabled为false，defaultLevel为SIMPLE；ResourceLeakDetector还有TARGET_RECORDS(io.netty.leakDetection.targetRecords)及SAMPLING_INTERVAL(io.netty.leakDetection.samplingInterval)两个属性，其中targetRecords默认为4，samplingInterval默认为128
    •  
  
  • ResourceLeakDetector提供了track方法用于创建ResourceLeakTracker；track方法内部调用track0方法，如果level为PARANOID则立即调用reportLeak，创建DefaultResourceLeak，否则利用随机数来判断(PlatformDependent.threadLocalRandom().nextInt(samplingInterval)) == 0)是否调用reportLeak并创建DefaultResourceLeak；reportLeak方法有个for循环，不断从refQueue取DefaultResourceLeak，然后调用reportUntracedLeak或者reportTracedLeak进行error
    •  
 
 
 
DefaultResourceLeak
 
 
netty-common-4.1.33.Final-sources.jar!/io/netty/util/ResourceLeakDetector.java
 
 
    private static final class DefaultResourceLeak
            extends WeakReference implements ResourceLeakTracker, ResourceLeak {

        @SuppressWarnings("unchecked") // generics and updaters do not mix.
        private static final AtomicReferenceFieldUpdater, Record> headUpdater =
                (AtomicReferenceFieldUpdater)
                        AtomicReferenceFieldUpdater.newUpdater(DefaultResourceLeak.class, Record.class, "head");

        @SuppressWarnings("unchecked") // generics and updaters do not mix.
        private static final AtomicIntegerFieldUpdater> droppedRecordsUpdater =
                (AtomicIntegerFieldUpdater)
                        AtomicIntegerFieldUpdater.newUpdater(DefaultResourceLeak.class, "droppedRecords");

        @SuppressWarnings("unused")
        private volatile Record head;
        @SuppressWarnings("unused")
        private volatile int droppedRecords;

        private final Set> allLeaks;
        private final int trackedHash;

        DefaultResourceLeak(
                Object referent,
                ReferenceQueue refQueue,
                Set> allLeaks) {
            super(referent, refQueue);

            assert referent != null;

            // Store the hash of the tracked object to later assert it in the close(...) method.
            // It's important that we not store a reference to the referent as this would disallow it from
            // be collected via the WeakReference.
            trackedHash = System.identityHashCode(referent);
            allLeaks.add(this);
            // Create a new Record so we always have the creation stacktrace included.
            headUpdater.set(this, new Record(Record.BOTTOM));
            this.allLeaks = allLeaks;
        }

        @Override
        public void record() {
            record0(null);
        }

        @Override
        public void record(Object hint) {
            record0(hint);
        }

        /**
         * This method works by exponentially backing off as more records are present in the stack. Each record has a
         * 1 / 2^n chance of dropping the top most record and replacing it with itself. This has a number of convenient
         * properties:
         *
         * 
    
         * 
  1.   The current record is always recorded. This is due to the compare and swap dropping the top most
         *       record, rather than the to-be-pushed record.
         * 
  2.   The very last access will always be recorded. This comes as a property of 1.
         * 
  3.   It is possible to retain more records than the target, based upon the probability distribution.
         * 
  4.   It is easy to keep a precise record of the number of elements in the stack, since each element has to
         *     know how tall the stack is.
         * 

         *
         * In this particular implementation, there are also some advantages. A thread local random is used to decide
         * if something should be recorded. This means that if there is a deterministic access pattern, it is now
         * possible to see what other accesses occur, rather than always dropping them. Second, after
         * {@link #TARGET_RECORDS} accesses, backoff occurs. This matches typical access patterns,
         * where there are either a high number of accesses (i.e. a cached buffer), or low (an ephemeral buffer), but
         * not many in between.
         *
         * The use of atomics avoids serializing a high number of accesses, when most of the records will be thrown
         * away. High contention only happens when there are very few existing records, which is only likely when the
         * object isn't shared! If this is a problem, the loop can be aborted and the record dropped, because another
         * thread won the race.
         */
        private void record0(Object hint) {
            // Check TARGET_RECORDS > 0 here to avoid similar check before remove from and add to lastRecords
            if (TARGET_RECORDS > 0) {
                Record oldHead;
                Record prevHead;
                Record newHead;
                boolean dropped;
                do {
                    if ((prevHead = oldHead = headUpdater.get(this)) == null) {
                        // already closed.
                        return;
                    }
                    final int numElements = oldHead.pos + 1;
                    if (numElements >= TARGET_RECORDS) {
                        final int backOffFactor = Math.min(numElements - TARGET_RECORDS, 30);
                        if (dropped = PlatformDependent.threadLocalRandom().nextInt(1 << backOffFactor) != 0) {
                            prevHead = oldHead.next;
                        }
                    } else {
                        dropped = false;
                    }
                    newHead = hint != null ? new Record(prevHead, hint) : new Record(prevHead);
                } while (!headUpdater.compareAndSet(this, oldHead, newHead));
                if (dropped) {
                    droppedRecordsUpdater.incrementAndGet(this);
                }
            }
        }

        boolean dispose() {
            clear();
            return allLeaks.remove(this);
        }

        @Override
        public boolean close() {
            if (allLeaks.remove(this)) {
                // Call clear so the reference is not even enqueued.
                clear();
                headUpdater.set(this, null);
                return true;
            }
            return false;
        }

        @Override
        public boolean close(T trackedObject) {
            // Ensure that the object that was tracked is the same as the one that was passed to close(...).
            assert trackedHash == System.identityHashCode(trackedObject);

            try {
                return close();
            } finally {
                // This method will do `synchronized(trackedObject)` and we should be sure this will not cause deadlock.
                // It should not, because somewhere up the callstack should be a (successful) `trackedObject.release`,
                // therefore it is unreasonable that anyone else, anywhere, is holding a lock on the trackedObject.
                // (Unreasonable but possible, unfortunately.)
                reachabilityFence0(trackedObject);
            }
        }

         /**
         * Ensures that the object referenced by the given reference remains
         * strongly reachable,
         * regardless of any prior actions of the program that might otherwise cause
         * the object to become unreachable; thus, the referenced object is not
         * reclaimable by garbage collection at least until after the invocation of
         * this method.
         *
         * 
 Recent versions of the JDK have a nasty habit of prematurely deciding objects are unreachable.
         * see: https://stackoverflow.com/questions/26642153/finalize-called-on-strongly-reachable-object-in-java-8
         * The Java 9 method Reference.reachabilityFence offers a solution to this problem.
         *
         * 
 This method is always implemented as a synchronization on {@code ref}, not as
         * {@code Reference.reachabilityFence} for consistency across platforms and to allow building on JDK 6-8.
         * It is the caller's responsibility to ensure that this synchronization will not cause deadlock.
         *
         * @param ref the reference. If {@code null}, this method has no effect.
         * @see java.lang.ref.Reference#reachabilityFence
         */
        private static void reachabilityFence0(Object ref) {
            if (ref != null) {
                // Empty synchronized is ok: https://stackoverflow.com/a/31933260/1151521
                synchronized (ref) { }
            }
        }

        @Override
        public String toString() {
            Record oldHead = headUpdater.getAndSet(this, null);
            if (oldHead == null) {
                // Already closed
                return EMPTY_STRING;
            }

            final int dropped = droppedRecordsUpdater.get(this);
            int duped = 0;

            int present = oldHead.pos + 1;
            // Guess about 2 kilobytes per stack trace
            StringBuilder buf = new StringBuilder(present * 2048).append(NEWLINE);
            buf.append("Recent access records: ").append(NEWLINE);

            int i = 1;
            Set seen = new HashSet(present);
            for (; oldHead != Record.BOTTOM; oldHead = oldHead.next) {
                String s = oldHead.toString();
                if (seen.add(s)) {
                    if (oldHead.next == Record.BOTTOM) {
                        buf.append("Created at:").append(NEWLINE).append(s);
                    } else {
                        buf.append('#').append(i++).append(':').append(NEWLINE).append(s);
                    }
                } else {
                    duped++;
                }
            }

            if (duped > 0) {
                buf.append(": ")
                        .append(duped)
                        .append(" leak records were discarded because they were duplicates")
                        .append(NEWLINE);
            }

            if (dropped > 0) {
                buf.append(": ")
                   .append(dropped)
                   .append(" leak records were discarded because the leak record count is targeted to ")
                   .append(TARGET_RECORDS)
                   .append(". Use system property ")
                   .append(PROP_TARGET_RECORDS)
                   .append(" to increase the limit.")
                   .append(NEWLINE);
            }

            buf.setLength(buf.length() - NEWLINE.length());
            return buf.toString();
        }
    } 
 
     
  
  • DefaultResourceLeak是ResourceLeakDetector定义的私有静态类，它继承了WeakReference类，同时实现了ResourceLeakTracker(定义了record、close方法)接口；record方法内部调用的是record0方法，它会更新newHead为新的Record；close方法会移除allLeaks，allLeaks由ResourceLeakDetector创建DefaultResourceLeak时传入，每创建一个DefaultResourceLeak，DefaultResourceLeak会把自己加入到allLeaks中
    •  
 
 
 
SimpleLeakAwareByteBuf
 
 
netty-netty-4.1.33.Final/buffer/src/main/java/io/netty/buffer/SimpleLeakAwareByteBuf.java
 
 
class SimpleLeakAwareByteBuf extends WrappedByteBuf {

    /**
     * This object's is associated with the {@link ResourceLeakTracker}. When {@link ResourceLeakTracker#close(Object)}
     * is called this object will be used as the argument. It is also assumed that this object is used when
     * {@link ResourceLeakDetector#track(Object)} is called to create {@link #leak}.
     */
    private final ByteBuf trackedByteBuf;
    final ResourceLeakTracker leak;

    SimpleLeakAwareByteBuf(ByteBuf wrapped, ByteBuf trackedByteBuf, ResourceLeakTracker leak) {
        super(wrapped);
        this.trackedByteBuf = ObjectUtil.checkNotNull(trackedByteBuf, "trackedByteBuf");
        this.leak = ObjectUtil.checkNotNull(leak, "leak");
    }

    SimpleLeakAwareByteBuf(ByteBuf wrapped, ResourceLeakTracker leak) {
        this(wrapped, wrapped, leak);
    }

    //......

    @Override
    public boolean release() {
        if (super.release()) {
            closeLeak();
            return true;
        }
        return false;
    }

    @Override
    public boolean release(int decrement) {
        if (super.release(decrement)) {
            closeLeak();
            return true;
        }
        return false;
    }

    private void closeLeak() {
        // Close the ResourceLeakTracker with the tracked ByteBuf as argument. This must be the same that was used when
        // calling DefaultResourceLeak.track(...).
        boolean closed = leak.close(trackedByteBuf);
        assert closed;
    }

    private ByteBuf unwrappedDerived(ByteBuf derived) {
        // We only need to unwrap SwappedByteBuf implementations as these will be the only ones that may end up in
        // the AbstractLeakAwareByteBuf implementations beside slices / duplicates and "real" buffers.
        ByteBuf unwrappedDerived = unwrapSwapped(derived);

        if (unwrappedDerived instanceof AbstractPooledDerivedByteBuf) {
            // Update the parent to point to this buffer so we correctly close the ResourceLeakTracker.
            ((AbstractPooledDerivedByteBuf) unwrappedDerived).parent(this);

            ResourceLeakTracker newLeak = AbstractByteBuf.leakDetector.track(derived);
            if (newLeak == null) {
                // No leak detection, just return the derived buffer.
                return derived;
            }
            return newLeakAwareByteBuf(derived, newLeak);
        }
        return newSharedLeakAwareByteBuf(derived);
    }

    //......
}
 
 
     
  
  • SimpleLeakAwareByteBuf继承了WrappedByteBuf，它的构造器要求传入ResourceLeakTracker
    •  
  
  • SimpleLeakAwareByteBuf覆盖了WrappedByteBuf的retainedSlice、retainedDuplicate、readRetainedSlice方法，它们内部都会调用unwrappedDerived方法，unwrappedDerived方法在unwrappedDerived对象是AbstractPooledDerivedByteBuf类型时会调用AbstractByteBuf.leakDetector.track进行track
    •  
  
  • SimpleLeakAwareByteBuf也覆盖了WrappedByteBuf的release方法，在调用父类release成功时会再调用closeLeak方法，使用leak.close(trackedByteBuf)来释放trackedByteBuf
    •  
 
 
 
AdvancedLeakAwareByteBuf
 
 
netty-netty-4.1.33.Final/buffer/src/main/java/io/netty/buffer/AdvancedLeakAwareByteBuf.java
 
 
final class AdvancedLeakAwareByteBuf extends SimpleLeakAwareByteBuf {

    private static final String PROP_ACQUIRE_AND_RELEASE_ONLY = "io.netty.leakDetection.acquireAndReleaseOnly";
    private static final boolean ACQUIRE_AND_RELEASE_ONLY;

    private static final InternalLogger logger = InternalLoggerFactory.getInstance(AdvancedLeakAwareByteBuf.class);

    static {
        ACQUIRE_AND_RELEASE_ONLY = SystemPropertyUtil.getBoolean(PROP_ACQUIRE_AND_RELEASE_ONLY, false);

        if (logger.isDebugEnabled()) {
            logger.debug("-D{}: {}", PROP_ACQUIRE_AND_RELEASE_ONLY, ACQUIRE_AND_RELEASE_ONLY);
        }

        ResourceLeakDetector.addExclusions(
                AdvancedLeakAwareByteBuf.class, "touch", "recordLeakNonRefCountingOperation");
    }

    AdvancedLeakAwareByteBuf(ByteBuf buf, ResourceLeakTracker leak) {
        super(buf, leak);
    }

    AdvancedLeakAwareByteBuf(ByteBuf wrapped, ByteBuf trackedByteBuf, ResourceLeakTracker leak) {
        super(wrapped, trackedByteBuf, leak);
    }

    static void recordLeakNonRefCountingOperation(ResourceLeakTracker leak) {
        if (!ACQUIRE_AND_RELEASE_ONLY) {
            leak.record();
        }
    }

    //......

    @Override
    public ByteBuf order(ByteOrder endianness) {
        recordLeakNonRefCountingOperation(leak);
        return super.order(endianness);
    }

    @Override
    public ByteBuf slice() {
        recordLeakNonRefCountingOperation(leak);
        return super.slice();
    }

    @Override
    public ByteBuf slice(int index, int length) {
        recordLeakNonRefCountingOperation(leak);
        return super.slice(index, length);
    }

    //......

    @Override
    public ByteBuf retain() {
        leak.record();
        return super.retain();
    }

    @Override
    public ByteBuf retain(int increment) {
        leak.record();
        return super.retain(increment);
    }

    @Override
    public boolean release() {
        leak.record();
        return super.release();
    }

    @Override
    public boolean release(int decrement) {
        leak.record();
        return super.release(decrement);
    }

    @Override
    public ByteBuf touch() {
        leak.record();
        return this;
    }

    @Override
    public ByteBuf touch(Object hint) {
        leak.record(hint);
        return this;
    }

    //......
}
 
 
     
  
  • AdvancedLeakAwareByteBuf继承了SimpleLeakAwareByteBuf，它对方法进行了覆盖，这些覆盖的方法要么内部通过recordLeakNonRefCountingOperation调用leak.record，要么直接调用leak.record
    •  
 
 
 
小结
 
 
     
  
  • ResourceLeakDetector使用Level枚举定义了四种不同的leak detection级别，分别是DISABLED、SIMPLE、ADVANCED、PARANOID；默认level为SIMPLE；可以使用-Dio.netty.leakDetection.level=advanced来进行设置；ResourceLeakDetector还有TARGET_RECORDS(io.netty.leakDetection.targetRecords)及SAMPLING_INTERVAL(io.netty.leakDetection.samplingInterval)两个属性，其中targetRecords默认为4，samplingInterval默认为128
    •  
  
  • ResourceLeakDetector提供了track方法用于创建ResourceLeakTracker；track方法内部调用track0方法，如果level为PARANOID则立即调用reportLeak，创建DefaultResourceLeak，否则利用随机数来判断(PlatformDependent.threadLocalRandom().nextInt(samplingInterval)) == 0)是否调用reportLeak并创建DefaultResourceLeak；reportLeak方法有个for循环，不断从refQueue取DefaultResourceLeak，然后调用reportUntracedLeak或者reportTracedLeak进行error
    •  
  
  • DefaultResourceLeak是ResourceLeakDetector定义的私有静态类，它继承了WeakReference类，同时实现了ResourceLeakTracker(定义了record、close方法)接口；record方法内部调用的是record0方法，它会更新newHead为新的Record；close方法会移除allLeaks，allLeaks由ResourceLeakDetector创建DefaultResourceLeak时传入，每创建一个DefaultResourceLeak，DefaultResourceLeak会把自己加入到allLeaks中
    •  
  
  • SimpleLeakAwareByteBuf继承了WrappedByteBuf，它的构造器要求传入ResourceLeakTracker；SimpleLeakAwareByteBuf覆盖了WrappedByteBuf的retainedSlice、retainedDuplicate、readRetainedSlice方法，它们内部都会调用unwrappedDerived方法，unwrappedDerived方法在unwrappedDerived对象是AbstractPooledDerivedByteBuf类型时会调用AbstractByteBuf.leakDetector.track进行track；SimpleLeakAwareByteBuf也覆盖了WrappedByteBuf的release方法，在调用父类release成功时会再调用closeLeak方法，使用leak.close(trackedByteBuf)来释放trackedByteBuf
    •  
  
  • AdvancedLeakAwareByteBuf继承了SimpleLeakAwareByteBuf，它对方法进行了覆盖，这些覆盖的方法要么内部通过recordLeakNonRefCountingOperation调用leak.record，要么直接调用leak.record；另外有SimpleLeakAwareCompositeByteBuf与AdvancedLeakAwareCompositeByteBuf，它们对leak detect的支持类似SimpleLeakAwareByteBuf与AdvancedLeakAwareByteBuf
    •  
 
 
 
doc
 
 
     
  
  • Netty 的资源泄露探测机制
    •  
  
  • A Netty ByteBuf Memory Leak Story and the Lessons Learned
    •  
  
  • In 4.0.23.Final, Seeing io.netty.util.ResourceLeakDetector - LEAK: ByteBuf.release() was not called before it's garbage-collected #2774
    •  
 
 

                            
                        
                    
                    
                    

                    
                    
                    

                
                

                    
                

            
        
    
    

        
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                        王小工
javaudp网络协议网络javanio
                        
    Netty在UDP（用户数据报协议，UserDatagramProtocol）通信中的应用非常广泛，特别是在对实时性要求较高、对数据准确性要求相对较低的场景中，如视频传输、语音通信等。以下是对Netty在UDP通信中的详细解析：一、UDP协议简介UDP是一种无连接的协议，它并不在通信双方之间建立连接，而是直接将数据包从发送端发送到接收端。UDP不保证数据包的可靠传输，也不保证数据包的顺序，因此其传
    
                    
    • 
                    
  • 【四、使用Netty编写UDP应用】
                        ThinkLess404
Netty网络编程udp网络协议网络
                        
    编写UDP应用目标创建UDPServer创建ServerHandler创建UDP客户端创建客户端的Handler目标之前的章节我们学习了编码服务端，使用TCP通信，本章我们学习如何使用Netty构建一个UDP应用。创建UDPServerpackagecom.coman404.base;importcom.coman404.base.handler.UDPServerHandler;importio
    
                    
    • 
                    
  • linux部署jar项目报错_linux jar 服务
                        国家级做梦冠军
linux部署jar项目报错
                        
    关于linuxjar服务的搜索结果问题linux重启netty服务一些问题，请大神进linux上部署netty架构的服务时我一般启动的时候用下面脚本nohupjava-jarxxx-xxx.jarstart80808888&关闭的时候杀进程就可以了。今天部署的时候启动服务就报userBind，于是我查...杨冬芳2019-12-0120:26:501161浏览量回答数0问题Linux下Tomcat
    
                    
    • 
                    
  • Spring Cloud全解析：网关之GateWay简介
                        拾光师
springcloudjava
                        
    GateWay简介由于zuul升级为zuul2时，netflix公司内部出现了分歧，所以springcloud自己研发了一套网关gateway，提供一种简单有效的方式来对API进行路由，以及提供一些强大的过滤器功能，如：熔断、限流、重试等，基于WebFlux框架实现的，底层使用了高性能的Reactor模式通信框架Netty特性基于spring5和springboot2构建动态路由：能够匹配任何请求
    
                    
    • 
                    
  • Netty+WebSocket实现高并发网络编程
                        Sunny_yiyi
Java精英阶级JavaWebSocket网络websocket网络协议
                        
    我们来实现一个Netty+WebSocket集成案例，由于Netty+WebSocket集成代码比较麻烦，我们可以利用目前开源的项目netty-websocket-spring-boot-starter轻松实现Netty和WebSocket的集成。我们搭建一个项目，项目叫seckill-message，用于处理通知用户抢单状态。1)pom.xmlorg.yeauty</groupId
    
                    
    • 
                    
  • Spring Boot 一个极简且完整的后台框架
                        搬砖养女人
数据库架构javaspringsqltomcat
                        
    一个完整的极简后台框架，方便做小项目的时候可以快速开发。这里面多贴图片和代码，做个参考吧，代码可以下载下来自己看看，里面这套后台模板不错，喜欢的拿去。先放几张图imageimageimage项目介绍SpringBoot，实现了一个极简单的后台框架image小编提供免费的Java架构学习资料（里面有高可用、高并发、高性能及分布式、Jvm性能调优、Spring源码，MyBatis，Netty,Redi
    
                    
    • 
                    
  • netty编程
                        chenjunxu

                        
    需要导包：netty-all-4.1.25.Final或者导入依赖：io.nettynetty-all4.1.25.Final定义一个server类：publicclassHelloServer{publicstaticvoidmain(String[]args){//定义一对线程组//主线程组,用于接受客户端的连接，但是不做任何处理，跟老板一样，不做事EventLoopGroupbossGrou
    
                    
    • 
                    
  • Simple RPC - 05 从零开始设计一个客户端（下）_ 依赖倒置和SPI
                        小小工匠
【SimpleRPC】rpc网络协议网络
                        
    文章目录Pre概述依赖倒置原则与解耦设计与实现1.定义接口来隔离调用方与实现类2.实现类`DynamicStubFactory`3.调用方与实现类的解耦依赖注入与SPI的解耦依赖注入SPI（ServiceProviderInterface）总结PreSimpleRPC-01框架原理及总体架构初探SimpleRPC-02通用高性能序列化和反序列化设计与实现SimpleRPC-03借助Netty实现异
    
                    
    • 
                    
  • 使用Netty实现 WebSocket至Socket的消息转发服务
                        Leon-aHandler
websocket服务器网络协议nettyspringboot
                        
    业务需求场景：通过网页发送指令至硬件设备，并在连接过程中能够接收来自硬件设备的实时参数信息中转服务器逻辑：服务器内实现了一个websocket服务端和一个socket客户端，设置全局保存的ChannelGroup进行消息的转发。项目框架使用的是Springboot代码地址：https://github.com/Leon-aHandler/Netty-relayDemo
    
                    
    • 
                    
  • Netty Websocket
                        王小工
javawebsocketjavanio
                        
    一、WebSocket协议概述WebSocket是一种在单个TCP连接上进行全双工通信的协议。它允许服务端主动向客户端推送数据，从而实现了实时通信。WebSocket建立在HTTP之上，但与HTTP的轮询（Polling）和长轮询（LongPolling）相比，WebSocket只需一次握手，即可在客户端和服务器之间建立持久的连接，并通过这个连接进行双向数据传输。二、Netty框架简介Netty是
    
                    
    • 
                    
  • Netty 实现 WebSocket 协议
                        最业余的程序猿
nettywebsocket网络协议网络
                        
    要使用Netty框架实现WebSocket服务端与客户端通信，你需要按照以下步骤进行：1、添加依赖首先，在你的项目中引入Netty和其WebSocket支持库的依赖。如果你使用Maven构建项目，可以在pom.xml文件中添加相应的依赖项。Maven:io.nettynetty-all4.1.77.Finalorg.springframework.bootspring-boot-starter-w
    
                    
    • 
                                
  • 数据采集高并发的架构应用
                                    3golden
.net
                                    
    问题的出发点： 
 
         最近公司为了发展需要，要扩大对用户的信息采集，每个用户的采集量估计约2W。如果用户量增加的话，将会大量照成采集量成3W倍的增长，但是又要满足日常业务需要，特别是指令要及时得到响应的频率次数远大于预期。 
      &n
    
                                
    • 
                                
  • 不停止 MySQL 服务增加从库的两种方式
                                    brotherlamp
linuxlinux视频linux资料linux教程linux自学
                                    
    现在生产环境MySQL数据库是一主一从，由于业务量访问不断增大，故再增加一台从库。前提是不能影响线上业务使用，也就是说不能重启MySQL服务，为了避免出现其他情况，选择在网站访问量低峰期时间段操作。 
 一般在线增加从库有两种方式，一种是通过mysqldump备份主库，恢复到从库，mysqldump是逻辑备份，数据量大时，备份速度会很慢，锁表的时间也会很长。另一种是通过xtrabacku
    
                                
    • 
                                
  • Quartz——SimpleTrigger触发器
                                    eksliang
SimpleTriggerTriggerUtilsquartz
                                    
    转载请出自出处：http://eksliang.iteye.com/blog/2208166 一.概述 
SimpleTrigger触发器，当且仅需触发一次或者以固定时间间隔周期触发执行； 
  二.SimpleTrigger的构造函数 
 
 SimpleTrigger(String name, String group)：通过该构造函数指定Trigger所属组和名称； 
 Simpl
    
                                
    • 
                                
  • Informatica应用（1）
                                    18289753290
sqlworkflowlookup组件Informatica
                                    
    1.如果要在workflow中调用shell脚本有一个command组件，在里面设置shell的路径；调度wf可以右键出现schedule，现在用的是HP的tidal调度wf的执行。 
2.designer里面的router类似于SSIS中的broadcast（多播组件）;Reset_Workflow_Var：参数重置 （比如说我这个参数初始是1在workflow跑得过程中变成了3我要在结束时还要
    
                                
    • 
                                
  • python 获取图片验证码中文字
                                    酷的飞上天空
python
                                    
    根据现成的开源项目 http://code.google.com/p/pytesser/改写 
在window上用easy_install安装不上  看了下源码发现代码很少  于是就想自己改写一下 
  
添加支持网络图片的直接解析 
  
  
#coding:utf-8 
#import sys 
#reload(sys) 
#sys.s
    
                                
    • 
                                
  • AJAX
                                    永夜-极光
Ajax
                                    
    1.AJAX功能:动态更新页面,减少流量消耗,减轻服务器负担 
  
2.代码结构: 
   
<html>

<head>
<script type="text/javascript">
function loadXMLDoc()
{
.... AJAX script goes here ...

    
                                
    • 
                                
  • 创业OR读研
                                    随便小屋
创业
                                    
            现在研一，有种想创业的想法，不知道该不该去实施。因为对于的我情况这两者是矛盾的，可能就是鱼与熊掌不能兼得。 
       
        研一的生活刚刚过去两个月，我们学校主要的是
    
                                
    • 
                                
  • 需求做得好与坏直接关系着程序员生活质量
                                    aijuans
IT 生活
                                    
      
        这个故事还得从去年换工作的事情说起，由于自己不太喜欢第一家公司的环境我选择了换一份工作。去年九月份我入职现在的这家公司，专门从事金融业内软件的开发。十一月份我们整个项目组前往北京做现场开发，从此苦逼的日子开始了。 
       系统背景：五月份就有同事前往甲方了解需求一直到6月份，后续几个月也完
    
                                
    • 
                                
  • 如何定义和区分高级软件开发工程师
                                    aoyouzi

                                    
    在软件开发领域，高级开发工程师通常是指那些编写代码超过 3 年的人。这些人可能会被放到领导的位置，但经常会产生非常糟糕的结果。Matt Briggs 是一名高级开发工程师兼 Scrum 管理员。他认为，单纯使用年限来划分开发人员存在问题，两个同样具有 10 年开发经验的开发人员可能大不相同。近日，他发表了一篇博文，根据开发者所能发挥的作用划分软件开发工程师的成长阶段。 
　　初
    
                                
    • 
                                
  • Servlet的请求与响应
                                    百合不是茶
servletget提交java处理post提交
                                    
      
Servlet是tomcat中的一个重要组成,也是负责客户端和服务端的中介 
  
  
1,Http的请求方式(get  ,post); 
  客户端的请求一般都会都是Servlet来接受的,在接收之前怎么来确定是那种方式提交的,以及如何反馈,Servlet中有相应的方法,  http的get方式 servlet就是都doGet(
    
                                
    • 
                                
  • web.xml配置详解之listener
                                    bijian1013
javaweb.xmllistener
                                    
    一.定义 
<listener>  
	<listen-class>com.myapp.MyListener</listen-class>  
</listener> 
  
二.作用        该元素用来注册一个监听器类。可以收到事件什么时候发生以及用什么作为响
    
                                
    • 
                                
  • Web页面性能优化（yahoo技术）
                                    Bill_chen
JavaScriptAjaxWebcssYahoo
                                    
    1.尽可能的减少HTTP请求数 content 
2.使用CDN server 
3.添加Expires头(或者 Cache-control) server 
4.Gzip 组件 server 
5.把CSS样式放在页面的上方。 css 
6.将脚本放在底部(包括内联的) javascript 
7.避免在CSS中使用Expressions css 
8.将javascript和css独立成外部文
    
                                
    • 
                                
  • 【MongoDB学习笔记八】MongoDB游标、分页查询、查询结果排序
                                    bit1129
mongodb
                                    
    游标 
  
游标，简单的说就是一个查询结果的指针。游标作为数据库的一个对象，使用它是包括 
 
 声明 
 打开 
 循环抓去一定数目的文档直到结果集中的所有文档已经抓取完 
 关闭游标 
 
  
游标的基本用法，类似于JDBC的ResultSet(hasNext判断是否抓去完,next移动游标到下一条文档)，在获取一个文档集时，可以提供一个类似JDBC的FetchSize
    
                                
    • 
                                
  • ORA-12514 TNS 监听程序当前无法识别连接描述符中请求服务 的解决方法
                                    白糖_
ORA-12514
                                    
     今天通过Oracle SQL*Plus连接远端服务器的时候提示“监听程序当前无法识别连接描述符中请求服务”，遂在网上找到了解决方案： 
 ①打开Oracle服务器安装目录\NETWORK\ADMIN\listener.ora文件，你会看到如下信息： 
  
# listener.ora Network Configuration File: D:\database\Oracle\net
    
                                
    • 
                                
  • Eclipse 问题 A resource exists with a different case
                                    bozch
eclipse
                                    
    在使用Eclipse进行开发的时候，出现了如下的问题： 
Description Resource Path Location TypeThe project was not built due to "A resource exists with a different case: '/SeenTaoImp_zhV2/bin/seentao'.&
    
                                
    • 
                                
  • 编程之美-小飞的电梯调度算法
                                    bylijinnan
编程之美
                                    
    

public class AptElevator {

	/**
	 * 编程之美 小飞 电梯调度算法
	 * 在繁忙的时间，每次电梯从一层往上走时，我们只允许电梯停在其中的某一层。
	 * 所有乘客都从一楼上电梯，到达某层楼后，电梯听下来，所有乘客再从这里爬楼梯到自己的目的层。
	 * 在一楼时，每个乘客选择自己的目的层，电梯则自动计算出应停的楼层。
	 * 问：电梯停在哪
    
                                
    • 
                                
  • SQL注入相关概念
                                    chenbowen00
sqlWeb安全
                                    
    SQL Injection：就是通过把SQL命令插入到Web表单递交或输入域名或页面请求的查询字符串，最终达到欺骗服务器执行恶意的SQL命令。 
 
具体来说，它是利用现有应用程序，将（恶意）的SQL命令注入到后台数据库引擎执行的能力，它可以通过在Web表单中输入（恶意）SQL语句得到一个存在安全漏洞的网站上的数据库，而不是按照设计者意图去执行SQL语句。 
 
首先让我们了解什么时候可能发生SQ
    
                                
    • 
                                
  • [光与电]光子信号战防御原理
                                    comsci
原理
                                    
     
 
      无论是在战场上,还是在后方,敌人都有可能用光子信号对人体进行控制和攻击,那么采取什么样的防御方法,最简单,最有效呢? 
 
      我们这里有几个山寨的办法,可能有些作用,大家如果有兴趣可以去实验一下 
 
      根据光
    
                                
    • 
                                
  • oracle 11g新特性:Pending Statistics
                                    daizj
oracledbms_stats
                                    
    oracle 11g新特性:Pending Statistics 转 
 
从11g开始，表与索引的统计信息收集完毕后，可以选择收集的统信息立即发布，也可以选择使新收集的统计信息处于pending状态，待确定处于pending状态的统计信息是安全的，再使处于pending状态的统计信息发布，这样就会避免一些因为收集统计信息立即发布而导致SQL执行计划走错的灾难。 
 
在 11g 之前的版本中，D
    
                                
    • 
                                
  • 快速理解RequireJs
                                    dengkane
jqueryrequirejs
                                    
    RequireJs已经流行很久了，我们在项目中也打算使用它。它提供了以下功能： 
 
 声明不同js文件之间的依赖 
 可以按需、并行、延时载入js库 
 可以让我们的代码以模块化的方式组织 
 
初看起来并不复杂。 在html中引入requirejs 
在HTML中，添加这样的 <script> 标签： 
<script src="/path/to
    
                                
    • 
                                
  • C语言学习四流程控制if条件选择、for循环和强制类型转换
                                    dcj3sjt126com
c
                                    
    # include <stdio.h>

int main(void)
{
	int i, j;

	scanf("%d %d", &i, &j);

	if (i > j)
		printf("i大于j\n");
	else
		printf("i小于j\n");

	retu
    
                                
    • 
                                
  • dictionary的使用要注意
                                    dcj3sjt126com
IO
                                    
    NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:
                          user.user_id , @"id",
                          user.username , @"username",
         
    
                                
    • 
                                
  • Android 中的资源访问(Resource)
                                    finally_m
xmlandroidStringdrawablecolor
                                    
     
简单的说，Android中的资源是指非代码部分。例如，在我们的Android程序中要使用一些图片来设置界面，要使用一些音频文件来设置铃声，要使用一些动画来显示特效，要使用一些字符串来显示提示信息。那么，这些图片、音频、动画和字符串等叫做Android中的资源文件。 
在Eclipse创建的工程中，我们可以看到res和assets两个文件夹，是用来保存资源文件的，在assets中保存的一般是原生
    
                                
    • 
                                
  • Spring使用Cache、整合Ehcache
                                    234390216
springcacheehcache@Cacheable
                                    
    Spring使用Cache 
  
  
       从3.1开始，Spring引入了对Cache的支持。其使用方法和原理都类似于Spring对事务管理的支持。Spring Cache是作用在方法上的，其核心思想是这样的：当我们在调用一个缓存方法时会把该方法参数和返回结果作为一个键值对存放在缓存中，等到下次利用同样的
    
                                
    • 
                                
  • 当druid遇上oracle blob(clob)
                                    jackyrong
oracle
                                    
    http://blog.csdn.net/renfufei/article/details/44887371 
 
众所周知，Oracle有很多坑, 所以才有了去IOE。 
 
在使用Druid做数据库连接池后，其实偶尔也会碰到小坑，这就是使用开源项目所必须去填平的。【如果使用不开源的产品，那就不是坑，而是陷阱了，你都不知道怎么去填坑】 
 
用Druid连接池，通过JDBC往Oracle数据库的
    
                                
    • 
                                
  • easyui datagrid pagination获得分页页码、总页数等信息
                                    ldzyz007

                                    
    var grid = $('#datagrid');  
var options = grid.datagrid('getPager').data("pagination").options;  
var curr = options.pageNumber;  
var total = options.total;  
var max =
    
                                
    • 
                                
  • 浅析awk里的数组
                                    nigelzeng
二维数组array数组awk
                                    
    awk绝对是文本处理中的神器，它本身也是一门编程语言，还有许多功能本人没有使用到。这篇文章就单单针对awk里的数组来进行讨论，如何利用数组来帮助完成文本分析。 
  
有这么一组数据： 
   abcd,91#31#2012-12-31 11:24:00 
case_a,136#19#2012-12-31 11:24:00 
case_a,136#23#2012-12-31 1
    
                                
    • 
                                
  • 搭建 CentOS 6 服务器(6) - TigerVNC
                                    rensanning
centos
                                    
    安装GNOME桌面环境 
 
# yum groupinstall "X Window System" "Desktop" 
 
 
安装TigerVNC 
 
# yum -y install tigervnc-server tigervnc 
 
 
启动VNC服务 
 
# /etc/init.d/vncserver restart
# vncser
    
                                
    • 
                                
  • Spring 数据库连接整理
                                    tomcat_oracle
springbeanjdbc
                                    
    1、数据库连接jdbc.properties配置详解  　　jdbc.url=jdbc:hsqldb:hsql://localhost/xdb   　　jdbc.username=sa   　　jdbc.password=   　　jdbc.driver=不同的数据库厂商驱动，此处不一一列举   　　接下来，详细配置代码如下：   　　 
Spring连接池      
    
                                
    • 
                                
  • Dom4J解析使用xpath java.lang.NoClassDefFoundError: org/jaxen/JaxenException异常
                                    xp9802

                                    
    用Dom4J解析xml,以前没注意,今天使用dom4j包解析xml时在xpath使用处报错 
     异常栈：java.lang.NoClassDefFoundError: org/jaxen/JaxenException异常  
     导入包 jaxen-1.1-beta-6.jar 解决; 
&nb
    
                                
    •