Tracing Agent原理

以 User调用project-test-projectA为例

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http://ali03:8888/projectA/admin

User -> Tomcat7 -> SpringMvc(projectA/{name})-> 线程内调用 -> FeignClient(projectB/{name})

EntrySpan

• ContextManager.createEntrySpan()

• TracingContext#createEntrySpan()
  检测EntrySpan是否已创建，如果是，则不会创建新的EntrySpan，只是重新调用一下其start()方法即可

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  public AbstractSpan createEntrySpan(final String operationName) { // 默认配置下，每个TraceSegment只能放300个Span if (isLimitMechanismWorking()) { NoopSpan span = new NoopSpan(); // 超过300就放NoopSan return push(span); // 将Span记录到activeSpanStack栈中 } AbstractSpan entrySpan; TracingContext owner = this; final AbstractSpan parentSpan = peek(); // 读取栈顶Span,即当前Span final int parentSpanId = parentSpan == null ? -1 : parentSpan.getSpanId(); if (parentSpan != null && parentSpan.isEntry()) { profilingRecheck(parentSpan, operationName); // 更新operationName parentSpan.setOperationName(operationName); entrySpan = parentSpan; // 重新调用start()方法，strart()方法会重置operationName之外的其他字段 return entrySpan.start(); } else { // 新建EntrySpan对象，spanIdGenerator生成Span ID并递增 entrySpan = new EntrySpan( spanIdGenerator++, parentSpanId, operationName, owner ); // 调用start方法，第一次调用start()方法会设置startTime entrySpan.start(); // 将新建的Span添加到activeSpanStack栈的栈顶 return push(entrySpan); } }

  LocalSpan

• ContextManager#createLocalSpan()

• TracingContext#createLocalSpan()

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if (isLimitMechanismWorking()) {
    NoopSpan span = new NoopSpan();
    return push(span);
}
// 从activeSpanStack栈顶获取当前Span
AbstractSpan parentSpan = peek();
final int parentSpanId = parentSpan == null ? -1 : parentSpan.getSpanId();
// 新建LocalSpan对象
AbstractTracingSpan span = new LocalSpan(spanIdGenerator++, parentSpanId, operationName, this);
  // 调用start方法，第一次调用start()方法会设置startTime
span.start();
// 将新建的Span添加到activeSpanStack栈的栈顶
return push(span);
}

ExitSpan

• ContextManager#createExitSpan()
• TraingContext#createExitSpan()

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public AbstractSpan createExitSpan(final String operationName, final String remotePeer) {
    if (isLimitMechanismWorking()) {
        NoopExitSpan span = new NoopExitSpan(remotePeer);
        return push(span);
    }

    AbstractSpan exitSpan;
    // 从activeSpanStack栈顶获取当前Span
    AbstractSpan parentSpan = peek();
    TracingContext owner = this;
    if (parentSpan != null && parentSpan.isExit()) {
        // 当前Span已经是ExitSpan，则不再新建ExitSpan，而是调用其start()方法
        exitSpan = parentSpan;
    } else {
        // 当前Span不是ExitSpan，就新建一个ExitSpan
        final int parentSpanId = parentSpan == null ? -1 : parentSpan.getSpanId();
        exitSpan = new ExitSpan(spanIdGenerator++, parentSpanId, operationName, remotePeer, owner);
        // 将新建的ExitSpan入栈
        push(exitSpan);
    }
    // 调用start()方法
    exitSpan.start();
    return exitSpan;
}

stopSpan()

• ContextManager.stopSpan()
• TracingContext#stopSpan()
  会将当前activeSpanStack栈顶的Span关闭并出栈，同时整个activeSpanStack栈空了之后，会尝试关闭当前TraceSegment。

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  public boolean stopSpan(AbstractSpan span) { // 获取当前栈顶的Span对象 AbstractSpan lastSpan = peek(); if (lastSpan == span) { // 只能关闭当前活跃的Span对象，否则抛出异常 if (lastSpan instanceof AbstractTracingSpan) { AbstractTracingSpan toFinishSpan = (AbstractTracingSpan) lastSpan; //添加span到segment中 并记录结束时间 if (toFinishSpan.finish(segment)) { // 尝试关闭Span // 当Span完全关闭之后，会将其出栈(即从activeSpanStack中删除) pop(); } } else { pop(); } } else { throw new IllegalStateException("Stopping the unexpected span = " + span); } //如果该节点是最后一个节点 finish(); return activeSpanStack.isEmpty(); }

  关闭TraceSegment

  放入内存队列中，等待发送collector

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  private void finish() { if (isRunningInAsyncMode) { asyncFinishLock.lock(); } try { boolean isFinishedInMainThread = activeSpanStack.isEmpty() && running; if (isFinishedInMainThread) { /* * Notify after tracing finished in the main thread. */ TracingThreadListenerManager.notifyFinish(this); } //TraceSegmentServiceClient#afterFinished()放入内存队列中 if (isFinishedInMainThread && (!isRunningInAsyncMode || asyncSpanCounter == 0)) { TraceSegment finishedSegment = segment.finish(isLimitMechanismWorking()); TracingContext.ListenerManager.notifyFinish(finishedSegment); running = false; } } finally { if (isRunningInAsyncMode) { asyncFinishLock.unlock(); } } }