聊聊rocketmq的AsyncAppender

序

本文主要研究一下rocketmq的AsyncAppender

AsyncAppender

org/apache/rocketmq/logging/inner/LoggingBuilder.java

public static class AsyncAppender extends Appender implements Appender.AppenderPipeline {

        public static final int DEFAULT_BUFFER_SIZE = 128;

        private final List<LoggingEvent> buffer = new ArrayList<LoggingEvent>();

        private final Map<String, DiscardSummary> discardMap = new HashMap<String, DiscardSummary>();

        private int bufferSize = DEFAULT_BUFFER_SIZE;

        private final AppenderPipelineImpl appenderPipeline;

        private final Thread dispatcher;

        private boolean blocking = true;

        public AsyncAppender() {
            appenderPipeline = new AppenderPipelineImpl();

            dispatcher = new Thread(new Dispatcher(this, buffer, discardMap, appenderPipeline));

            dispatcher.setDaemon(true);

            dispatcher.setName("AsyncAppender-Dispatcher-" + dispatcher.getName());
            dispatcher.start();
        }

        public void addAppender(final Appender newAppender) {
            synchronized (appenderPipeline) {
                appenderPipeline.addAppender(newAppender);
            }
        }

        public void append(final LoggingEvent event) {
            if ((dispatcher == null) || !dispatcher.isAlive() || (bufferSize <= 0)) {
                synchronized (appenderPipeline) {
                    appenderPipeline.appendLoopOnAppenders(event);
                }

                return;
            }

            event.getThreadName();
            event.getRenderedMessage();

            synchronized (buffer) {
                while (true) {
                    int previousSize = buffer.size();

                    if (previousSize < bufferSize) {
                        buffer.add(event);

                        if (previousSize == 0) {
                            buffer.notifyAll();
                        }

                        break;
                    }

                    boolean discard = true;
                    if (blocking
                        && !Thread.interrupted()
                        && Thread.currentThread() != dispatcher) {
                        try {
                            buffer.wait();
                            discard = false;
                        } catch (InterruptedException e) {
                            Thread.currentThread().interrupt();
                        }
                    }
                    if (discard) {
                        String loggerName = event.getLoggerName();
                        DiscardSummary summary = discardMap.get(loggerName);

                        if (summary == null) {
                            summary = new DiscardSummary(event);
                            discardMap.put(loggerName, summary);
                        } else {
                            summary.add(event);
                        }

                        break;
                    }
                }
            }
        }

        public void close() {

            synchronized (buffer) {
                closed = true;
                buffer.notifyAll();
            }

            try {
                dispatcher.join();
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
                SysLogger.error(
                    "Got an InterruptedException while waiting for the "
                        + "dispatcher to finish.", e);
            }

            synchronized (appenderPipeline) {
                Enumeration iter = appenderPipeline.getAllAppenders();
                if (iter != null) {
                    while (iter.hasMoreElements()) {
                        Object next = iter.nextElement();
                        if (next instanceof Appender) {
                            ((Appender) next).close();
                        }
                    }
                }
            }
        }

        public Enumeration getAllAppenders() {
            synchronized (appenderPipeline) {
                return appenderPipeline.getAllAppenders();
            }
        }

        public Appender getAppender(final String name) {
            synchronized (appenderPipeline) {
                return appenderPipeline.getAppender(name);
            }
        }

        public boolean isAttached(final Appender appender) {
            synchronized (appenderPipeline) {
                return appenderPipeline.isAttached(appender);
            }
        }

        public void removeAllAppenders() {
            synchronized (appenderPipeline) {
                appenderPipeline.removeAllAppenders();
            }
        }

        public void removeAppender(final Appender appender) {
            synchronized (appenderPipeline) {
                appenderPipeline.removeAppender(appender);
            }
        }

        public void removeAppender(final String name) {
            synchronized (appenderPipeline) {
                appenderPipeline.removeAppender(name);
            }
        }

        public void setBufferSize(final int size) {
            if (size < 0) {
                throw new NegativeArraySizeException("size");
            }

            synchronized (buffer) {
                bufferSize = (size < 1) ? 1 : size;
                buffer.notifyAll();
            }
        }

        public int getBufferSize() {
            return bufferSize;
        }

        public void setBlocking(final boolean value) {
            synchronized (buffer) {
                blocking = value;
                buffer.notifyAll();
            }
        }

        public boolean getBlocking() {
            return blocking;
        }

    }

• 初始化Dispatcher，构造器调用Dispatcher的start，然后close方法调用dispatcher.join()
• append方法会判断buffer够不够，够的话往buffer添加事件，不够则丢弃同时进行DiscardSummary统计
• dispatcher则从buffer消费日志然后做真正的append

DiscardSummary

private final class DiscardSummary {

            private LoggingEvent maxEvent;

            private int count;

            public DiscardSummary(final LoggingEvent event) {
                maxEvent = event;
                count = 1;
            }

            public void add(final LoggingEvent event) {
                if (event.getLevel().toInt() > maxEvent.getLevel().toInt()) {
                    maxEvent = event;
                }
                count++;
            }

            public LoggingEvent createEvent() {
                String msg =
                    MessageFormat.format(
                        "Discarded {0} messages due to full event buffer including: {1}",
                        count, maxEvent.getMessage());

                return new LoggingEvent(
                    "AsyncAppender.DONT_REPORT_LOCATION",
                    Logger.getLogger(maxEvent.getLoggerName()),
                    maxEvent.getLevel(),
                    msg,
                    null);
            }
        }

• 记录LoggingEvent及其丢弃的次数

Dispatcher

private class Dispatcher implements Runnable {

            private final AsyncAppender parent;

            private final List<LoggingEvent> buffer;

            private final Map<String, DiscardSummary> discardMap;

            private final AppenderPipelineImpl appenderPipeline;

            public Dispatcher(
                final AsyncAppender parent, final List<LoggingEvent> buffer, final Map<String, DiscardSummary> discardMap,
                final AppenderPipelineImpl appenderPipeline) {

                this.parent = parent;
                this.buffer = buffer;
                this.appenderPipeline = appenderPipeline;
                this.discardMap = discardMap;
            }

            public void run() {
                boolean isActive = true;

                try {
                    while (isActive) {
                        LoggingEvent[] events = null;

                        synchronized (buffer) {
                            int bufferSize = buffer.size();
                            isActive = !parent.closed;

                            while ((bufferSize == 0) && isActive) {
                                buffer.wait();
                                bufferSize = buffer.size();
                                isActive = !parent.closed;
                            }

                            if (bufferSize > 0) {
                                events = new LoggingEvent[bufferSize + discardMap.size()];
                                buffer.toArray(events);

                                int index = bufferSize;
                                Collection<DiscardSummary> values = discardMap.values();
                                for (DiscardSummary value : values) {
                                    events[index++] = value.createEvent();
                                }

                                buffer.clear();
                                discardMap.clear();

                                buffer.notifyAll();
                            }
                        }
                        if (events != null) {
                            for (LoggingEvent event : events) {
                                synchronized (appenderPipeline) {
                                    appenderPipeline.appendLoopOnAppenders(event);
                                }
                            }
                        }
                    }
                } catch (InterruptedException ex) {
                    Thread.currentThread().interrupt();
                }
            }
        }

• 这里锁住buffer，然后调用buffer.toArray(events)，得到LoggingEvent数组，之后循环遍历调用appenderPipeline.appendLoopOnAppenders(event)

AppenderPipelineImpl

public static class AppenderPipelineImpl implements AppenderPipeline {


        protected Vector<Appender> appenderList;

        public void addAppender(Appender newAppender) {
            if (newAppender == null) {
                return;
            }

            if (appenderList == null) {
                appenderList = new Vector<Appender>(1);
            }
            if (!appenderList.contains(newAppender)) {
                appenderList.addElement(newAppender);
            }
        }

        public int appendLoopOnAppenders(LoggingEvent event) {
            int size = 0;
            Appender appender;

            if (appenderList != null) {
                size = appenderList.size();
                for (int i = 0; i < size; i++) {
                    appender = appenderList.elementAt(i);
                    appender.doAppend(event);
                }
            }
            return size;
        }

        public Enumeration getAllAppenders() {
            if (appenderList == null) {
                return null;
            } else {
                return appenderList.elements();
            }
        }

        public Appender getAppender(String name) {
            if (appenderList == null || name == null) {
                return null;
            }

            int size = appenderList.size();
            Appender appender;
            for (int i = 0; i < size; i++) {
                appender = appenderList.elementAt(i);
                if (name.equals(appender.getName())) {
                    return appender;
                }
            }
            return null;
        }

        public boolean isAttached(Appender appender) {
            if (appenderList == null || appender == null) {
                return false;
            }

            int size = appenderList.size();
            Appender a;
            for (int i = 0; i < size; i++) {
                a = appenderList.elementAt(i);
                if (a == appender) {
                    return true;
                }
            }
            return false;
        }

        public void removeAllAppenders() {
            if (appenderList != null) {
                int len = appenderList.size();
                for (int i = 0; i < len; i++) {
                    Appender a = appenderList.elementAt(i);
                    a.close();
                }
                appenderList.removeAllElements();
                appenderList = null;
            }
        }

        public void removeAppender(Appender appender) {
            if (appender == null || appenderList == null) {
                return;
            }
            appenderList.removeElement(appender);
        }

        public void removeAppender(String name) {
            if (name == null || appenderList == null) {
                return;
            }
            int size = appenderList.size();
            for (int i = 0; i < size; i++) {
                if (name.equals((appenderList.elementAt(i)).getName())) {
                    appenderList.removeElementAt(i);
                    break;
                }
            }
        }

    }

• 这里的appendLoopOnAppenders方法，会挨个对appender进行doAppend操作

小结

rocketmq的这个AsyncAppender实现不是很高效，大量地锁住buffer进行append以及appendLoopOnAppenders

doc

• LoggingBuilder