async_hooks: add trace events to async_hooks

This will allow trace event to record timing information for all
asynchronous operations that are observed by async_hooks.

PR-URL: https://github.com/nodejs/node/pull/15538
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

lib/internal/trace_events_async_hooks.js

@@ -0,0 +1,67 @@
+'use strict';
+
+const trace_events = process.binding('trace_events');
+const async_wrap = process.binding('async_wrap');
+const async_hooks = require('async_hooks');
+
+// Use small letters such that chrome://traceing groups by the name.
+// The behaviour is not only useful but the same as the events emitted using
+// the specific C++ macros.
+const BEFORE_EVENT = 'b'.charCodeAt(0);
+const END_EVENT = 'e'.charCodeAt(0);
+
+// In trace_events it is not only the id but also the name that needs to be
+// repeated. Since async_hooks doesn't expose the provider type in the
+// non-init events, use a map to manually map the asyncId to the type name.
+const typeMemory = new Map();
+
+// It is faster to emit trace_events directly from C++. Thus, this happens in
+// async_wrap.cc. However, events emitted from the JavaScript API or the
+// Embedder C++ API can't be emitted from async_wrap.cc. Thus they are
+// emitted using the JavaScript API. To prevent emitting the same event
+// twice the async_wrap.Providers list is used to filter the events.
+const nativeProviders = new Set(Object.keys(async_wrap.Providers));
+
+const hook = async_hooks.createHook({
+  init(asyncId, type, triggerAsyncId, resource) {
+    if (nativeProviders.has(type)) return;
+
+    typeMemory.set(asyncId, type);
+    trace_events.emit(BEFORE_EVENT, 'node.async_hooks',
+                      type, asyncId, 'triggerAsyncId', triggerAsyncId);
+  },
+
+  before(asyncId) {
+    const type = typeMemory.get(asyncId);
+    if (type === undefined) return;
+
+    trace_events.emit(BEFORE_EVENT, 'node.async_hooks',
+                      type + '_CALLBACK', asyncId);
+  },
+
+  after(asyncId) {
+    const type = typeMemory.get(asyncId);
+    if (type === undefined) return;
+
+    trace_events.emit(END_EVENT, 'node.async_hooks',
+                      type + '_CALLBACK', asyncId);
+  },
+
+  destroy(asyncId) {
+    const type = typeMemory.get(asyncId);
+    if (type === undefined) return;
+
+    trace_events.emit(END_EVENT, 'node.async_hooks',
+                      type, asyncId);
+
+    // cleanup asyncId to type map
+    typeMemory.delete(asyncId);
+  }
+});
+
+
+exports.setup = function() {
+  if (trace_events.categoryGroupEnabled('node.async_hooks')) {
+    hook.enable();
+  }
+};