add metrics to track span lifecycle in debug mode (#1896)

packages/dd-trace/src/opentracing/span.js

@@ -1,16 +1,23 @@
 'use strict'
 
+// TODO (new internal tracer): use DC events for lifecycle metrics and test them
+
 const opentracing = require('opentracing')
 const now = require('performance-now')
+const semver = require('semver')
 const Span = opentracing.Span
 const SpanContext = require('./span_context')
 const id = require('../id')
 const tagger = require('../tagger')
+const metrics = require('../metrics')
 const log = require('../log')
 const { storage } = require('../../../datadog-core')
 
 const { DD_TRACE_EXPERIMENTAL_STATE_TRACKING } = process.env
 
+const unfinishedRegistry = createRegistry('unfinished')
+const finishedRegistry = createRegistry('finished')
+
 class DatadogSpan extends Span {
   constructor (tracer, processor, prioritySampler, fields, debug) {
     super()
@@ -25,13 +32,21 @@ class DatadogSpan extends Span {
     this._processor = processor
     this._prioritySampler = prioritySampler
     this._store = storage.getStore()
+    this._name = operationName
 
     this._spanContext = this._createContext(parent)
     this._spanContext._name = operationName
     this._spanContext._tags = tags
     this._spanContext._hostname = hostname
 
     this._startTime = fields.startTime || this._getTime()
+
+    if (this._debug && unfinishedRegistry) {
+      metrics.increment('runtime.node.spans.unfinished')
+      metrics.increment('runtime.node.spans.unfinished.by.name', `span_name:${operationName}`)
+
+      unfinishedRegistry.register(this, operationName, this)
+    }
   }
 
   toString () {
@@ -122,6 +137,16 @@ class DatadogSpan extends Span {
       }
     }
 
+    if (this._debug && finishedRegistry) {
+      metrics.decrement('runtime.node.spans.unfinished')
+      metrics.decrement('runtime.node.spans.unfinished.by.name', `span_name:${this._name}`)
+      metrics.increment('runtime.node.spans.finished')
+      metrics.increment('runtime.node.spans.finished.by.name', `span_name:${this._name}`)
+
+      unfinishedRegistry.unregister(this)
+      finishedRegistry.register(this, this._name)
+    }
+
     finishTime = parseFloat(finishTime) || this._getTime()
 
     this._duration = finishTime - this._startTime
@@ -131,4 +156,13 @@ class DatadogSpan extends Span {
   }
 }
 
+function createRegistry (type) {
+  if (!semver.satisfies(process.version, '>=14.6')) return
+
+  return new global.FinalizationRegistry(name => {
+    metrics.decrement(`runtime.node.spans.${type}`)
+    metrics.decrement(`runtime.node.spans.${type}.by.name`, [`span_name:${name}`])
+  })
+}
+
 module.exports = DatadogSpan