log4j2⽤asyncRoot配置异步⽇志是如何使⽤disruptor
⽤asyncRoot配置对应的对接disruptor类是AsyncLoggerConfigDisruptor,⽤Log4jContextSelector启动参数配置全局异步的对应的对接disruptor类
是AsyncLoggerDisruptor。下⾯分析的是AsyncLoggerConfigDisruptor
disruptor的创建与启动需要的部件实现
AsyncLoggerConfigDisruptor.start⽅法⽤来创建并启动disruptor实例
创建disruptor需要EventFactory，ringBuffer的⼤⼩，ThreadFactory，ProducerType，等待策略waitStrategy
创建后需要设置ExceptionHandler，设置EventHandler。
发布(⽣产)事件的translator。
EventFactory
分是否可变(mutable字段)场景对应两个不同的EventFactory。
不可变的factory的逻辑是：
@Override
public Log4jEventWrapper newInstance() {
return new Log4jEventWrapper();
}
可变的factory逻辑是：
public Log4jEventWrapper newInstance() {
return new Log4jEventWrapper(new MutableLogEvent());
}
会在Log4jEventWrapper的构造函数中传⼊MutableLogEvent实例。
ringBuffer的⼤⼩
是根据AsyncLoggerConfig.RingBufferSize配置值算出来的。
这个配置项的值最⼩不能⼩于128，默认值分两种情况进⾏设定：如果启⽤了ENABLE_THREADLOCALS(优化GC的⼀个配置项)，那么默认值是4 * 1024，否则是256 * 1024。
这个配置是通过System properties指定，同样存在不同版本，配置项名称不⼀致的情况，log4j2.asyncLoggerRingBufferSize (AsyncLogger.RingBufferSize)。详细可以参见
ThreadFactory
主要是定制线程名：
线程名格式是："AsyncLoggerConfig-" + FACTORY_NUMBER(⾃增) + "-" + threadFactoryName + "-" + THREAD_NUMBER(⾃增)
默认的实际⽰例是： Log4j2-TF-1-AsyncLoggerConfig--1，跟上⾯的有些差异，上⾯的分析错了吗？？
ProducerType
多⽣产者
等待策略waitStrategy
默认是10ms的TimeoutBlockingWaitStrategy。⽀持可配
置SleepingWaitStrategy、YieldingWaitStrategy、BlockingWaitStrategy、BusySpinWaitStrategy、TimeoutBlockingWaitStrategy。
这个配置是通过System properties指定，同样存在不同版本，配置项名称不⼀致的情况，log4j2.asyncLoggerWaitStrategy (AsyncLogger.WaitStrategy)。
ExceptionHandler
可以配置，配置项名称是AsyncLoggerConfig.ExceptionHandler，默认是⽤AsyncLoggerConfigDefaultExceptionHandler，打印: AsyncLogger error handling event seq=..., value=...，并打出异常栈。
EventHandler
此处使⽤了 Log4jEventWrapperHandler RingBufferLogEventHandler，是disruptor的SequenceReportingEventHandler实现。
/**
* EventHandler performs the work in a separate thread.
*/
private static class Log4jEventWrapperHandler implements SequenceReportingEventHandler<Log4jEventWrapper> {
private static final int NOTIFY_PROGRESS_THRESHOLD = 50;
private Sequence sequenceCallback;
private int counter;
@Override
public void setSequenceCallback(final Sequence sequenceCallback) {
this.sequenceCallback = sequenceCallback;
}
@Override
public void onEvent(final Log4jEventWrapper event, final long sequence, final boolean endOfBatch)
throws Exception {
event.event.setEndOfBatch(endOfBatch);
event.loggerConfig.asyncCallAppenders(event.event);
event.clear();
notifyIntermediateProgress(sequence);
}
/**
* Notify the BatchEventProcessor that the sequence has progressed. Without this callback the sequence would not
* be progressed until the batch has completely finished.
*/
private void notifyIntermediateProgress(final long sequence) {
if (++counter > NOTIFY_PROGRESS_THRESHOLD) {
sequenceCallback.set(sequence);
counter = 0;
}
}
}
event.loggerConfig.asyncCallAppenders(event.event); 这个会触发⽇志的输出
translator
跟EventFactory⼀样分mutable是否可变的两种情况。
不可变：
private static final EventTranslatorTwoArg<Log4jEventWrapper, LogEvent, AsyncLoggerConfig> TRANSLATOR =
new EventTranslatorTwoArg<Log4jEventWrapper, LogEvent, AsyncLoggerConfig>() {
@Override
public void translateTo(final Log4jEventWrapper ringBufferElement, final long sequence,
final LogEvent logEvent, final AsyncLoggerConfig loggerConfig) {
ringBufferElement.event = logEvent;
ringBufferElement.loggerConfig = loggerConfig;
}
};
可变：
log4j2不打印日志
/**
* Object responsible for passing on data to a RingBuffer event with a MutableLogEvent.
*/
private static final EventTranslatorTwoArg<Log4jEventWrapper, LogEvent, AsyncLoggerConfig> MUTABLE_TRANSLATOR =
new EventTranslatorTwoArg<Log4jEventWrapper, LogEvent, AsyncLoggerConfig>() {
@Override
public void translateTo(final Log4jEventWrapper ringBufferElement, final long sequence,
final LogEvent logEvent, final AsyncLoggerConfig loggerConfig) {
((MutableLogEvent) ringBufferElement.event).initFrom(logEvent);
ringBufferElement.loggerConfig = loggerConfig;
}
};
都是完成⼀个事情给ringBufferElement元素的event赋值或者初始化。
事件进队列的tryEnqueue⽅法逻辑分析
prepareEvent
1. ensureImmutable：创建LogEvent的快照，传递进来的原LogEvent在应⽤线程还会被继续修改，所以此处要创建快照
2. Log4jLogEvent.makeMessageImmutable：格式化消息。因为是异步⽇志，针对需要format的消息在此处进⾏格式化，否则会因为引
⽤对象值的改变导致⽇志不准确
tryPublishEvent
1. 发布事件对象到disruptor队列
事件出队列的处理
先看按下调⽤栈:
Daemon Thread [Log4j2-TF-1-AsyncLoggerConfig--1] (Suspended (breakpoint at line 37 in PatternFormatter))
PatternFormatter.format(LogEvent, StringBuilder) line: 37
Serializable(LogEvent, StringBuilder) line: 334
ConsoleAppender(AbstractOutputStreamAppender<M>).directEncodeEvent(LogEvent) line: 177
ConsoleAppender(AbstractOutputStreamAppender<M>).tryAppend(LogEvent) line: 170
ConsoleAppender(AbstractOutputStreamAppender<M>).append(LogEvent) line: 161
AppenderControl.callAppender0(LogEvent) line: 129
AppenderControl.callAppenderPreventRecursion(LogEvent) line: 120
AppenderControl.callAppender(LogEvent) line: 84
AsyncLoggerConfig(LoggerConfig).callAppenders(LogEvent) line: 448
AsyncLoggerConfig.asyncCallAppenders(LogEvent) line: 129
Event(AsyncLoggerConfigDisruptor$Log4jEventWrapper, long, boolean) line: 111
Event(Object, long, boolean) line: 97
BatchEventProcessor<T>.run() line: 129
Log4jThread(Thread).run() line: 748