痛点

查线上日志时，同一个 Pod 内多线程日志交错，很难追踪每个请求对应的日志信息。

日志收集工具将多个 Pod 的日志收集到同一个数据库中后，情况就更加混乱不堪了。

解决

TraceId + MDC

MDC：

https://logback.qos.ch/manual/mdc.html

publicvoiddoFilter(ServletRequest request, ServletResponse response, FilterChain chain)
throws IOException, ServletException {
HttpServletRequest httpServletRequest = (HttpServletRequest) request;
String traceId = httpServletRequest.getHeader(TRACE_ID_HEADER_KEY);
if (StrUtil.isBlank(traceId)) {
traceId =UUID.randomUUID().toString();
}
MDC.put(MDC_TRACE_ID_KEY, traceId);
try {
chain.doFilter(request, response);
} finally {
MDC.remove(MDC_TRACE_ID_KEY);
}
}
<?xml version="1.0" encoding="UTF-8"?>
<configuration debug="false">
<property name="pattern" value="[%d{yyyy-MM-dd HH:mm:ss.SSS}] %-5level [%thread] %logger %line [%X{traceId}] [%tid] - %msg%n"/>


整合 Feign

发起服务间调用时，需要将 MDC 中的 traceId 传递到被调用服务。我们项目中统一使用 Feign Client，实现服务间的 HTTP 远程调用，在 Feign RequestInterceptor 中，取出 MDC 中的 traceId，塞到请求头中：requestTemplate.header(TRACE_ID_HEADER_KEY, MDC.get(MDC_TRACE_ID_KEY));

@Override
publicvoidapply(RequestTemplate template) {
template.header(TRACE_ID_HEADER_KEY, MDC.get(MDC_TRACE_ID_KEY));
}


多线程适配

Please note that MDC as implemented by logback- classic assumes that values are placed into the MDC with moderate frequency. Also note that a child thread does not automatically inherit a copy of the mapped diagnostic context of its parent.

在子线程执行任务前，将父线程的 MDC 内容设置到子线程的 MDC 中；在子线程任务执行完成后，清除子线程 MDC 中的内容。

适配 JDK ThreadPoolExecutor：

public classMdcAwareThreadPoolExecutorextendsThreadPoolExecutor {
@Override
publicvoidexecute(Runnable command) {
Map<String, String> parentThreadContextMap =MDC.getCopyOfContextMap();
super.execute(MdcTaskUtils.adaptMdcRunnable(command, parentThreadContextMap));
}
}

适配 Spring TaskDecorator：


@Component
public classMdcAwareTaskDecoratorimplementsTaskDecorator {
@Override
public Runnable decorate(Runnable runnable) {
Map<String, String> parentThreadContextMap =MDC.getCopyOfContextMap();
return MdcTaskUtils.adaptMdcRunnable(runnable, parentThreadContextMap);
}
}

MdcTaskUtils#adaptMdcRunnable()：采用装饰者模式，装饰原生的 Runnable runnable 对象，在原生 Runnable 对象执行前，将父线程的 MDC 设置到子线程中，在原生 Runnable 对象执行结束后，清除子线程 MDC 中的内容。

@Slf4j
public abstract classMdcTaskUtils {
publicstatic Runnable adaptMdcRunnable(Runnable runnable, Map<String, String> parentThreadContextMap) {
return () -> {
log.debug("parentThreadContextMap: {}, currentThreadContextMap: {}", parentThreadContextMap,
MDC.getCopyOfContextMap());
if (MapUtils.isEmpty(parentThreadContextMap) ||!parentThreadContextMap.containsKey(MDC_TRACE_ID_KEY)) {
log.debug("can not find a parentThreadContextMap, maybe task is fired using async or schedule task.");
MDC.put(MDC_TRACE_ID_KEY, UUID.randomUUID().toString());
} else {
MDC.put(MDC_TRACE_ID_KEY, parentThreadContextMap.get(MDC_TRACE_ID_KEY));
}
try {
runnable.run();
} finally {
MDC.remove(MDC_TRACE_ID_KEY);
}
};
}
}


整合 Skywalking

Skywalking 官方提供了对 logback 1.x 版本的适配：apm-toolkit-logback-1.x，可以在 logback 中打印 skywalking traceId，可以将 X-App-Trace-Id 和 skywalking traceId 结合起来，方便接口业务和性能问题的排查。

layout 具体实现类选择 TraceIdPatternLogbackLayout。在 logback pattern 中使用 %tid 打印 skywalking traceId。

<?xml version="1.0" encoding="UTF-8"?>
<configuration debug="false">
<property name="pattern" value="[%d{yyyy-MM-dd HH:mm:ss.SSS}] %-5level [%thread] %logger %line [%X{traceId}] [%tid] - %msg%n"/>
<appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
<encoder class="ch.qos.logback.core.encoder.LayoutWrappingEncoder">
<layout class="org.apache.skywalking.apm.toolkit.log.logback.v1.x.TraceIdPatternLogbackLayout">
<pattern>${pattern}</pattern>
</layout>
</encoder>
</appender>

TraceIdPatternLogbackLayout 类初始化时，添加了两个 PatternConverter：

public classTraceIdPatternLogbackLayoutextendsPatternLayout {
publicTraceIdPatternLogbackLayout() {
}
static {
defaultConverterMap.put("tid", LogbackPatternConverter. class.getName());
defaultConverterMap.put("sw_ctx", LogbackSkyWalkingContextPatternConverter. class.getName());
}
}

LogbackPatternConverter#convert() 方法写死了返回 "TID: N/A"，这是怎么回事呢？

public classLogbackPatternConverterextends classicConverter {
publicLogbackPatternConverter() {
}
publicStringconvert(ILoggingEvent iLoggingEvent) {
return"TID: N/A";
}
}

启动 Java 应用时，指定 java agent 启动参数 -javaagent:-javaagent:/opt/tools/skywalking-agent.jar。skywalking agent 会代理 LogbackPatternConverter 类，重写 convert() 方法的逻辑。


package org.apache.skywalking.apm.toolkit.log.logback.v1.x;
import ch.qos.logback. classic.pattern. classicConverter;
import ch.qos.logback. classic.spi.ILoggingEvent;
import java.lang.reflect.Method;
import org.apache.skywalking.apm.agent.core.plugin.interceptor.enhance.EnhancedInstance;
import org.apache.skywalking.apm.agent.core.plugin.interceptor.enhance.InstMethodsInter;
import org.apache.skywalking.apm.toolkit.log.logback.v1.x.LogbackPatternConverter$auxiliary$pJ6Zrqzi;
public classLogbackPatternConverter
extends classicConverter
implementsEnhancedInstance {
private volatile Object _$Enhanced classField_ws;
publicstatic volatile /* synthetic */ InstMethodsInter delegate$mo3but1;
privatestatic final /* synthetic */ Method cachedValue$oeLgRjrq$u5j8qu3;
publicStringconvert(ILoggingEvent iLoggingEvent) {
return (String)delegate$mo3but1.intercept(this, newObject[]{iLoggingEvent}, newLogbackPatternConverter$auxiliary$pJ6Zrqzi(this, iLoggingEvent), cachedValue$oeLgRjrq$u5j8qu3);
}
private/* synthetic */Stringconvert$original$T8InTdln(ILoggingEvent iLoggingEvent) {
/*34*/return"TID: N/A";
}
@Override
publicvoidsetSkyWalkingDynamicField(Object object) {
this._$Enhanced classField_ws= object;
}
@Override
publicObjectgetSkyWalkingDynamicField() {
returnthis._$Enhanced classField_ws;
}
static {
classLoader.getSystem classLoader().load class("org.apache.skywalking.apm.dependencies.net.bytebuddy.dynamic.Nexus").getMethod("initialize", class. class, Integer.TYPE).invoke(null, LogbackPatternConverter. class, -1942176692);
cachedValue$oeLgRjrq$u5j8qu3 = LogbackPatternConverter. class.getMethod("convert", ILoggingEvent. class);
}
final /* synthetic */Stringconvert$original$T8InTdln$accessor$oeLgRjrq(ILoggingEvent iLoggingEvent) {
returnthis.convert$original$T8InTdln(iLoggingEvent);
}
}








MDC 原理

MDC 在 slf4j-api jar 包中，MDC 是 slf4j 的规范，对 MDC 的所有操作都会落到 MDCAdapter 接口的方法上。


public classMDC {
static final StringNULL_MDCA_URL="http://www.slf4j.org/codes.html#null_MDCA";
static final StringNO_STATIC_MDC_BINDER_URL="http://www.slf4j.org/codes.html#no_static_mdc_binder";
static MDCAdapter mdcAdapter;
publicstaticvoidput(String key, String val) throws IllegalArgumentException {
if (key ==null) {
thrownewIllegalArgumentException("key parameter cannot be null");
}
if (mdcAdapter ==null) {
thrownewIllegalStateException("MDCAdapter cannot be null. See also "+NULL_MDCA_URL);
}
mdcAdapter.put(key, val);
}
}


MDCAdapter 是 slf4j 提供的 MDC 适配器接口，也就是 MDC 的规范。任何日志框架想要使用 MDC 功能，需要遵守 MDCAdapter 接口接口规范，实现接口中的方法。

// This interface abstracts the service offered by various MDC implementations.
publicinterfaceMDCAdapter {
publicvoidput(String key, String val);
publicStringget(String key);
}


Logback 日志框架提供了对 MDCAdapter 的适配：LogbackMDCAdapter，底层采用 ThreadLocal 实现。


public classLogbackMDCAdapterimplementsMDCAdapter {
// The internal map is copied so as
// We wish to avoid unnecessarily copying of the map. To ensure
// efficient/timely copying, we have a variable keeping track of the last
// operation. A copy is necessary on 'put' or 'remove' but only if the last
// operation was a 'get'. Get operations never necessitate a copy nor
// successive 'put/remove' operations, only a get followed by a 'put/remove'
// requires copying the map.
// See http://jira.qos.ch/browse/LOGBACK-620 for the original discussion.
// We no longer use CopyOnInheritThreadLocal in order to solve LB classIC-183
// Initially the contents of the thread local in parent and child threads
// reference the same map. However, as soon as a thread invokes the put()
// method, the maps diverge as they should.
final ThreadLocal<Map<String, String>> copyOnThreadLocal =newThreadLocal<Map<String, String>>();
privatestatic final int WRITE_OPERATION=1;
privatestatic final int MAP_COPY_OPERATION=2;
// keeps track of the last operation performed
final ThreadLocal<Integer> lastOperation =newThreadLocal<Integer>();

publicvoidput(String key, String val) throws IllegalArgumentException {
if (key ==null) {
thrownewIllegalArgumentException("key cannot be null");
}
Map<String, String> oldMap = copyOnThreadLocal.get();
Integer lastOp =getAndSetLastOperation(WRITE_OPERATION);
if (wasLastOpReadOrNull(lastOp) || oldMap ==null) {
Map<String, String> newMap =duplicateAndInsertNewMap(oldMap);
newMap.put(key, val);
} else {
oldMap.put(key, val);
}
}
publicStringget(String key) {
final Map<String, String> map = copyOnThreadLocal.get();
if ((map !=null) && (key !=null)) {
return map.get(key);
} else {
returnnull;
}
}
}









Logback 占位符

PatternLayout 类初始化时，设置了 logback 常用占位符对应的 Converter。


public classPatternLayoutextendsPatternLayoutBase<ILoggingEvent> {
publicstatic final Map<String, String>DEFAULT_CONVERTER_MAP=newHashMap<String, String>();
publicstatic final Map<String, String>CONVERTER_ class_TO_KEY_MAP=newHashMap<String, String>();
/**
* @deprecated replaced by DEFAULT_CONVERTER_MAP
*/
publicstatic final Map<String, String> defaultConverterMap =DEFAULT_CONVERTER_MAP;
publicstatic final StringHEADER_PREFIX="#logback. classic pattern: ";
static {
DEFAULT_CONVERTER_MAP.putAll(Parser.DEFAULT_COMPOSITE_CONVERTER_MAP);
DEFAULT_CONVERTER_MAP.put("d", DateConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("date", DateConverter. class.getName());
CONVERTER_ class_TO_KEY_MAP.put(DateConverter. class.getName(), "date");
DEFAULT_CONVERTER_MAP.put("r", RelativeTimeConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("relative", RelativeTimeConverter. class.getName());
CONVERTER_ class_TO_KEY_MAP.put(RelativeTimeConverter. class.getName(), "relative");
DEFAULT_CONVERTER_MAP.put("level", LevelConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("le", LevelConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("p", LevelConverter. class.getName());
CONVERTER_ class_TO_KEY_MAP.put(LevelConverter. class.getName(), "level");

DEFAULT_CONVERTER_MAP.put("t", ThreadConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("thread", ThreadConverter. class.getName());
CONVERTER_ class_TO_KEY_MAP.put(ThreadConverter. class.getName(), "thread");
DEFAULT_CONVERTER_MAP.put("lo", LoggerConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("logger", LoggerConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("c", LoggerConverter. class.getName());
CONVERTER_ class_TO_KEY_MAP.put(LoggerConverter. class.getName(), "logger");
DEFAULT_CONVERTER_MAP.put("m", MessageConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("msg", MessageConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("message", MessageConverter. class.getName());
CONVERTER_ class_TO_KEY_MAP.put(MessageConverter. class.getName(), "message");
DEFAULT_CONVERTER_MAP.put("C", classOfCallerConverter. class.getName());
DEFAULT_CONVERTER_MAP.put(" class", classOfCallerConverter. class.getName());
CONVERTER_ class_TO_KEY_MAP.put( classOfCallerConverter. class.getName(), " class");
DEFAULT_CONVERTER_MAP.put("M", MethodOfCallerConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("method", MethodOfCallerConverter. class.getName());
CONVERTER_ class_TO_KEY_MAP.put(MethodOfCallerConverter. class.getName(), "method");
DEFAULT_CONVERTER_MAP.put("L", LineOfCallerConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("line", LineOfCallerConverter. class.getName());
CONVERTER_ class_TO_KEY_MAP.put(LineOfCallerConverter. class.getName(), "line");
DEFAULT_CONVERTER_MAP.put("F", FileOfCallerConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("file", FileOfCallerConverter. class.getName());
CONVERTER_ class_TO_KEY_MAP.put(FileOfCallerConverter. class.getName(), "file");
DEFAULT_CONVERTER_MAP.put("X", MDCConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("mdc", MDCConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("ex", ThrowableProxyConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("exception", ThrowableProxyConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("rEx", RootCauseFirstThrowableProxyConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("rootException", RootCauseFirstThrowableProxyConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("throwable", ThrowableProxyConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("xEx", ExtendedThrowableProxyConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("xException", ExtendedThrowableProxyConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("xThrowable", ExtendedThrowableProxyConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("nopex", NopThrowableInformationConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("nopexception", NopThrowableInformationConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("cn", ContextNameConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("contextName", ContextNameConverter. class.getName());
CONVERTER_ class_TO_KEY_MAP.put(ContextNameConverter. class.getName(), "contextName");
DEFAULT_CONVERTER_MAP.put("caller", CallerDataConverter. class.getName());
CONVERTER_ class_TO_KEY_MAP.put(CallerDataConverter. class.getName(), "caller");
DEFAULT_CONVERTER_MAP.put("marker", MarkerConverter. class.getName());
CONVERTER_ class_TO_KEY_MAP.put(MarkerConverter. class.getName(), "marker");
DEFAULT_CONVERTER_MAP.put("property", PropertyConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("n", LineSeparatorConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("black", BlackCompositeConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("red", RedCompositeConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("green", GreenCompositeConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("yellow", YellowCompositeConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("blue", BlueCompositeConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("magenta", MagentaCompositeConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("cyan", CyanCompositeConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("white", WhiteCompositeConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("gray", GrayCompositeConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("boldRed", BoldRedCompositeConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("boldGreen", BoldGreenCompositeConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("boldYellow", BoldYellowCompositeConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("boldBlue", BoldBlueCompositeConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("boldMagenta", BoldMagentaCompositeConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("boldCyan", BoldCyanCompositeConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("boldWhite", BoldWhiteCompositeConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("highlight", HighlightingCompositeConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("lsn", LocalSequenceNumberConverter. class.getName());
CONVERTER_ class_TO_KEY_MAP.put(LocalSequenceNumberConverter. class.getName(), "lsn");
DEFAULT_CONVERTER_MAP.put("prefix", PrefixCompositeConverter. class.getName());
}
}


























ThreadConverter：将 %thread 占位符转换为 logger 线程。

public classThreadConverterextends classicConverter {
publicStringconvert(ILoggingEvent event) {
return event.getThreadName();
}
)

在 PatternLayout 中，默认添加了对 MDC 的支持，可以将 %X{key} 或者 %mdc{key} 占位符转换为 MDC.get(key)。

DEFAULT_CONVERTER_MAP.put("X", MDCConverter. class.getName());
DEFAULT_CONVERTER_MAP.put("mdc", MDCConverter. class.getName());


MDCConverter 为何可以将 %X{traceId} 或者 %mdc{traceId} 占位符转换为 MDC.get("traceId") ？

在程序启动时，ch.qos.logback.core.pattern.parser.Compiler#compile() 会解析用户配置的 pattern 表达式，得到 pattern 中需要动态解析的占位符，比如 %d{yyyy-MM-dd HH:mm:ss.SSS}，%X{traceId}。将这些动态占位符传递给 DynamicConverter#optionList 字段（MDCConverter 本质就是 DynamicConverter），optionList 字段包含程序要处理的占位符名称，比如 traceId。

程序启动时，logback 进行 Convert 初始化，会调用 MDCConverter#start() 方法，将成员变量 private String key 的值设置为 traceId（MDCConverter#getFirstOption() 返回用户配置的 traceId）。

在 MDCConverter#convert() 方法中，将 traceId 占位符转换为 MDC.get(key)：String value = mdcPropertyMap.get(key)。


public classMDCConverterextends classicConverter {
privateString key;
privateString defaultValue ="";
@Override
publicvoidstart() {
String[] keyInfo =extractDefaultReplacement(getFirstOption());
key = keyInfo[0];
if (keyInfo[1] !=null) {
defaultValue = keyInfo[1];
}
super.start();
}
@Override
publicStringconvert(ILoggingEvent event) {
Map<String, String> mdcPropertyMap = event.getMDCPropertyMap();
if (mdcPropertyMap ==null) {
return defaultValue;
}
if (key ==null) {
returnoutputMDCForAllKeys(mdcPropertyMap);
} else {
String value = mdcPropertyMap.get(key);
if (value !=null) {
return value;
} else {
return defaultValue;
}
}
}
}






ILoggingEvent 接口的实现类 LoggingEvent 中，对 MDCAdapter 做了适配：


public classLoggingEventimplementsILoggingEvent {
publicMap<String, String>getMDCPropertyMap() {
// populate mdcPropertyMap if null
if (mdcPropertyMap ==null) {
MDCAdapter mdc =MDC.getMDCAdapter();
if (mdc instanceofLogbackMDCAdapter)
mdcPropertyMap = ((LogbackMDCAdapter) mdc).getPropertyMap();
else
mdcPropertyMap = mdc.getCopyOfContextMap();
}
// mdcPropertyMap still null, use emptyMap()
if (mdcPropertyMap ==null)
mdcPropertyMap = Collections.emptyMap();
return mdcPropertyMap;
}
}


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作者：OnebyWang

来源：https://juejin.cn/post/7278498472860581925

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