Add parallelism information to profiles (#4765)

packages/dd-trace/src/profiling/exporters/event_serializer.js

@@ -2,6 +2,22 @@ const os = require('os')
 const perf = require('perf_hooks').performance
 const version = require('../../../../../package.json').version
 
+const libuvThreadPoolSize = (() => {
+  const ss = process.env.UV_THREADPOOL_SIZE
+  if (ss === undefined) {
+    // Backend will apply the default size based on Node version.
+    return undefined
+  }
+  // libuv uses atoi to parse the value, which is almost the same as parseInt, except that parseInt
+  // will return NaN on invalid input, while atoi will return 0. This is handled at return.
+  const s = parseInt(ss)
+  // We dont' interpret the value further here in the library. Backend will interpret the number
+  // based on Node version. In all currently known Node versions, 0 results in 1 worker thread,
+  // negative values (because they're assigned to an unsigned int) become very high positive values,
+  // and the value is finally capped at 1024.
+  return isNaN(s) ? 0 : s
+})()
+
 class EventSerializer {
   constructor ({ env, host, service, version, libraryInjected, activation } = {}) {
     this._env = env
@@ -56,11 +72,16 @@ class EventSerializer {
           version
         },
         runtime: {
+          // os.availableParallelism only available in node 18.14.0/19.4.0 and above
+          available_processors: typeof os.availableParallelism === 'function'
+            ? os.availableParallelism()
+            : os.cpus().length,
           // Using `nodejs` for consistency with the existing `runtime` tag.
           // Note that the event `family` property uses `node`, as that's what's
           // proscribed by the Intake API, but that's an internal enum and is
           // not customer visible.
           engine: 'nodejs',
+          libuv_threadpool_size: libuvThreadPoolSize,
           // strip off leading 'v'. This makes the format consistent with other
           // runtimes (e.g. Ruby) but not with the existing `runtime_version` tag.
           // We'll keep it like this as we want cross-engine consistency. We

packages/dd-trace/test/profiling/exporters/agent.spec.js

@@ -115,7 +115,8 @@ describe('exporters/agent', function () {
     expect(event.info.profiler.ssi).to.have.property('mechanism', 'none')
     expect(event.info.profiler).to.have.property('version', version)
     expect(event.info).to.have.property('runtime')
-    expect(Object.keys(event.info.runtime)).to.have.length(2)
+    expect(Object.keys(event.info.runtime)).to.have.length(3)
+    expect(event.info.runtime).to.have.property('available_processors')
     expect(event.info.runtime).to.have.property('engine', 'nodejs')
     expect(event.info.runtime).to.have.property('version', process.version.substring(1))