一直沒弄明白sleuth的tracercontext是如何創建和傳遞的，閑來無事研究了一下。由于對sleuth的源碼不熟悉，準備通過debug brave.tracer的nextid()方法，查看方法調用棧來找來龍去脈。
首先創建兩個service a和b，記作srva、srvb，在srva中添加testa controller，sevb中添加testb controller，testa中通過feign調用testb。
先看當用戶通過瀏覽器調用srva的時候，srva是作為server的。
configuration:
tracewebservletautoconfiguration==>tracingfilter
tracehttpautoconfiguration==>httptracing
traceautoconfiguration==>tracing
sleuthlogautoconfiguration.slf4jconfiguration==>currenttracecontext
配置中，tracingfilter在實例化時需要一個httptracing：
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public static filter create(httptracing httptracing) { return new tracingfilter(httptracing);}//servlet運行時類final servletruntime servlet = servletruntime.get();//slf4jcurrenttracecontextfinal currenttracecontext currenttracecontext;final tracer tracer;final httpserverhandler<httpservletrequest, httpservletresponse> handler;//tracecontext的數據提取器final tracecontext.extractor<httpservletrequest> extractor;tracingfilter(httptracing httptracing) { tracer = httptracing.tracing().tracer(); currenttracecontext = httptracing.tracing().currenttracecontext(); handler = httpserverhandler.create(httptracing, adapter); extractor = httptracing.tracing().propagation().extractor(getter);} |
httptracing builder模式構造時接收一個tracing：
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tracing tracing;//客戶端span解析器httpclientparser clientparser;string servername;//服務端span解析器httpserverparser serverparser;httpsampler clientsampler, serversampler;builder(tracing tracing) { if (tracing == null) throw new nullpointerexception("tracing == null"); final errorparser errorparser = tracing.errorparser(); this.tracing = tracing; this.servername = ""; // override to re-use any custom error parser from the tracing component this.clientparser = new httpclientparser() { @override protected errorparser errorparser() { return errorparser; } }; this.serverparser = new httpserverparser() { @override protected errorparser errorparser() { return errorparser; } }; this.clientsampler = httpsampler.trace_id; this.serversampler(httpsampler.trace_id);} |
tracing實例化：
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@bean@conditionalonmissingbean// note: stable bean name as might be used outside sleuthtracing tracing(@value("${spring.zipkin.service.name:${spring.application.name:default}}") string servicename, propagation.factory factory, currenttracecontext currenttracecontext, reporter<zipkin2.span> reporter, sampler sampler, errorparser errorparser, sleuthproperties sleuthproperties) { return tracing.newbuilder() .sampler(sampler) .errorparser(errorparser) .localservicename(servicename) //extrafieldpropagation.factory .propagationfactory(factory) .currenttracecontext(currenttracecontext) .spanreporter(adjustedreporter(reporter)) .traceid128bit(sleuthproperties.istraceid128()) .supportsjoin(sleuthproperties.issupportsjoin()) .build();} |
下面看tracingfilter的dofilter：
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span span = handler.handlereceive(extractor, httprequest); // add attributes for explicit access to customization or span context request.setattribute(spancustomizer.class.getname(), span.customizer()); request.setattribute(tracecontext.class.getname(), span.context()); throwable error = null; scope scope = currenttracecontext.newscope(span.context()); try { // any downstream code can see tracer.currentspan() or use tracer.currentspancustomizer() chain.dofilter(httprequest, httpresponse); } catch (ioexception | servletexception | runtimeexception | error e) { error = e; throw e; } finally { scope.close(); if (servlet.isasync(httprequest)) { // we don't have the actual response, handle later servlet.handleasync(handler, httprequest, httpresponse, span); } else { // we have a synchronous response, so we can finish the span handler.handlesend(adapter.adaptresponse(httprequest, httpresponse), error, span); } }} |
在sleuthlogautoconfiguration中如果有slfj的包，則注入currenttracecontext：
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@configuration @conditionalonclass(mdc.class) @enableconfigurationproperties(sleuthslf4jproperties.class) protected static class slf4jconfiguration { @bean @conditionalonproperty(value = "spring.sleuth.log.slf4j.enabled", matchifmissing = true) @conditionalonmissingbean public currenttracecontext slf4jspanlogger() { return slf4jcurrenttracecontext.create(); } ... } |
slf4jcurrenttracecontext中，delegate就是currenttracecontext.default.inheritable()：
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public static final class default extends currenttracecontext { static final threadlocal<tracecontext> default = new threadlocal<>(); // inheritable as brave 3's threadlocalserverclientandlocalspanstate was inheritable static final inheritablethreadlocal<tracecontext> inheritable = new inheritablethreadlocal<>(); final threadlocal<tracecontext> local; //靜態方法create，local對象為threadlocal類型 /** uses a non-inheritable static thread local */ public static currenttracecontext create() { return new default(default); } //local對象為inheritablethreadlocal類型 //官方文檔指出，inheritable方法在線程池的環境中需謹慎使用，可能會取出錯誤的tracecontext，這樣會導致span等信息會記錄并關聯到錯誤的traceid上 /** * uses an inheritable static thread local which allows arbitrary calls to {@link * thread#start()} to automatically inherit this context. this feature is available as it is was * the default in brave 3, because some users couldn't control threads in their applications. * * <p>this can be a problem in scenarios such as thread pool expansion, leading to data being * recorded in the wrong span, or spans with the wrong parent. if you are impacted by this, * switch to {@link #create()}. */ public static currenttracecontext inheritable() { return new default(inheritable); } default(threadlocal<tracecontext> local) { if (local == null) throw new nullpointerexception("local == null"); this.local = local; } @override public tracecontext get() { return local.get(); } //替換當前tracecontext，close方法將之前的tracecontext設置回去 //scope接口繼承了closeable接口，在try中使用會自動調用close方法，為了避免用戶忘記close方法，還提供了runnable，callable，executor，executorservice包裝方法 @override public scope newscope(@nullable tracecontext currentspan) { final tracecontext previous = local.get(); local.set(currentspan); class defaultcurrenttracecontextscope implements scope { @override public void close() { local.set(previous); } } return new defaultcurrenttracecontextscope(); }} |
slf4jcurrenttracecontext的delegate使用的就是一個inheritablethreadlocal，inheritablethreadlocal在創建子線程的時候，會將父線程的inheritablethreadlocals繼承下來。這樣就實現了tracecontext在父子線程中的傳遞。
看一下currenttracecontext的maybescope：
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//返回一個新的scope，如果當前scope就是傳入的scope，返回一個空scopepublic scope maybescope(@nullable tracecontext currentspan) { //獲取當前tracecontext tracecontext currentscope = get(); //如果傳入的tracecontext為空，且當前tracecontext為空返回空scope if (currentspan == null) { if (currentscope == null) return scope.noop; return newscope(null); } return currentspan.equals(currentscope) ? scope.noop : newscope(currentspan);} |
tracingfilter中httpserverhandler解析request：請輸入代碼
2.srva請求到servb時作為client。
traceloadbalancerfeignclient-->loadbalancerfeignclient-->feignloadbalancer-->lazytracingfeignclient-->client
以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持服務器之家。
原文鏈接：https://segmentfault.com/a/1190000018115247
