src: add tracing category macros

Adds `TRACING_CATEGORY_NODE`, `TRACING_CATEGORY_NODE1` and
`TRACING_CATEGORY_NODE2` helper macros for consistently building
trace event category strings. For instance,

`TRACING_CATEGORY_NODE2(foo, bar)` would generate the category
string `node,node.foo,node.foo.bar`, such that...

```
TRACE_EVENT_NESTABLE_ASYNC_BEGIN0(
    TRACING_CATEGORY_NODE2(foo, bar),
    "baz", 1);
```

Would emit if trace events are enabled for categories: `node`,
`node.foo`, or `node.foo.bar`.

This allows a natural scoping down of what trace events a user
may want to receive. Enabling the `node` category would receive
everything Node.js produces.

PR-URL: https://github.com/nodejs/node/pull/19155
Reviewed-By: Andreas Madsen <amwebdk@gmail.com>

1 files changed, 7 insertions, 5 deletions

diff --git a/lib/internal/trace_events_async_hooks.js b/lib/internal/trace_events_async_hooks.js
index 704da98e14..db38fe99ad 100644
--- a/lib/internal/trace_events_async_hooks.js
+++ b/lib/internal/trace_events_async_hooks.js
@@ -15,6 +15,8 @@ const END_EVENT = 'e'.charCodeAt(0);
 // non-init events, use a map to manually map the asyncId to the type name.
 const typeMemory = new Map();
 
+const trace_event_category = 'node,node.async_hooks';
+
 // 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
@@ -27,7 +29,7 @@ const hook = async_hooks.createHook({
     if (nativeProviders.has(type)) return;
 
     typeMemory.set(asyncId, type);
-    trace_events.emit(BEFORE_EVENT, 'node.async_hooks',
+    trace_events.emit(BEFORE_EVENT, trace_event_category,
                       type, asyncId,
                       'triggerAsyncId', triggerAsyncId,
                       'executionAsyncId', async_hooks.executionAsyncId());
@@ -37,7 +39,7 @@ const hook = async_hooks.createHook({
     const type = typeMemory.get(asyncId);
     if (type === undefined) return;
 
-    trace_events.emit(BEFORE_EVENT, 'node.async_hooks',
+    trace_events.emit(BEFORE_EVENT, trace_event_category,
                       type + '_CALLBACK', asyncId);
   },
 
@@ -45,7 +47,7 @@ const hook = async_hooks.createHook({
     const type = typeMemory.get(asyncId);
     if (type === undefined) return;
 
-    trace_events.emit(END_EVENT, 'node.async_hooks',
+    trace_events.emit(END_EVENT, trace_event_category,
                       type + '_CALLBACK', asyncId);
   },
 
@@ -53,7 +55,7 @@ const hook = async_hooks.createHook({
     const type = typeMemory.get(asyncId);
     if (type === undefined) return;
 
-    trace_events.emit(END_EVENT, 'node.async_hooks',
+    trace_events.emit(END_EVENT, trace_event_category,
                       type, asyncId);
 
     // cleanup asyncId to type map
@@ -63,7 +65,7 @@ const hook = async_hooks.createHook({
 
 
 exports.setup = function() {
-  if (trace_events.categoryGroupEnabled('node.async_hooks')) {
+  if (trace_events.categoryGroupEnabled(trace_event_category)) {
     hook.enable();
   }
 };