lib: add tracing channel to diagnostics_channel

Author: Stephen Belanger

doc/api/diagnostics_channel.md

@@ -1,12 +1,18 @@
 'use strict';
 
 const {
+  ArrayPrototypeAt,
   ArrayPrototypeIndexOf,
   ArrayPrototypePush,
   ArrayPrototypeSplice,
+  FunctionPrototypeBind,
   ObjectCreate,
   ObjectGetPrototypeOf,
   ObjectSetPrototypeOf,
+  PromisePrototypeThen,
+  PromiseReject,
+  ReflectApply,
+  SafeMap,
   SymbolHasInstance,
 } = primordials;
 
@@ -23,11 +29,44 @@ const { triggerUncaughtException } = internalBinding('errors');
 
 const { WeakReference } = internalBinding('util');
 
+function decRef(channel) {
+  channel._weak.decRef();
+  if (channel._weak.getRef() === 0) {
+    delete channels[channel.name];
+  }
+}
+
+function markActive(channel) {
+  // eslint-disable-next-line no-use-before-define
+  ObjectSetPrototypeOf(channel, ActiveChannel.prototype);
+  channel._subscribers = [];
+  channel._stores = new SafeMap();
+}
+
+function maybeMarkInactive(channel) {
+  // When there are no more active subscribers, restore to fast prototype.
+  if (!channel._subscribers.length && !channel._stores.size) {
+    // eslint-disable-next-line no-use-before-define
+    ObjectSetPrototypeOf(channel, Channel.prototype);
+    channel._subscribers = undefined;
+    channel._stores = undefined;
+  }
+}
+
+function defaultTransform(data) {
+  return data
+}
+
+function wrapStoreRun(store, data, next, transform = defaultTransform) {
+  return () => store.run(transform(data), next);
+}
+
 // TODO(qard): should there be a C++ channel interface?
 class ActiveChannel {
   subscribe(subscription) {
     validateFunction(subscription, 'subscription');
     ArrayPrototypePush(this._subscribers, subscription);
+    this._weak.incRef();
   }
 
   unsubscribe(subscription) {
@@ -36,12 +75,28 @@ class ActiveChannel {
 
     ArrayPrototypeSplice(this._subscribers, index, 1);
 
-    // When there are no more active subscribers, restore to fast prototype.
-    if (!this._subscribers.length) {
-      // eslint-disable-next-line no-use-before-define
-      ObjectSetPrototypeOf(this, Channel.prototype);
+    decRef(this);
+    maybeMarkInactive(this);
+
+    return true;
+  }
+
+  bindStore(store, transform) {
+    const replacing = this._stores.has(store);
+    if (!replacing) this._weak.incRef();
+    this._stores.set(store, transform);
+  }
+
+  unbindStore(store) {
+    if (!this._stores.has(store)) {
+      return false;
     }
 
+    this._stores.delete(store);
+
+    decRef(this);
+    maybeMarkInactive(this);
+
     return true;
   }
 
@@ -61,11 +116,28 @@ class ActiveChannel {
       }
     }
   }
+
+  runStores(data, fn, thisArg, ...args) {
+    this.publish(data);
+
+    // Bind base fn first due to AsyncLocalStorage.run not having thisArg
+    fn = FunctionPrototypeBind(fn, thisArg, ...args);
+
+    for (const entry of this._stores.entries()) {
+      const store = entry[0];
+      const transform = entry[1];
+      fn = wrapStoreRun(store, data, fn, transform);
+    }
+
+    return fn();
+  }
 }
 
 class Channel {
   constructor(name) {
     this._subscribers = undefined;
+    this._stores = undefined;
+    this._weak = undefined;
     this.name = name;
   }
 
@@ -76,20 +148,32 @@ class Channel {
   }
 
   subscribe(subscription) {
-    ObjectSetPrototypeOf(this, ActiveChannel.prototype);
-    this._subscribers = [];
+    markActive(this);
     this.subscribe(subscription);
   }
 
   unsubscribe() {
     return false;
   }
 
+  bindStore(store, transform) {
+    markActive(this);
+    this.bindStore(store, transform);
+  }
+
+  unbindStore() {
+    return false;
+  }
+
   get hasSubscribers() {
     return false;
   }
 
   publish() {}
+
+  runStores(data, fn, thisArg, ...args) {
+    return ReflectApply(fn, thisArg, args);
+  }
 }
 
 const channels = ObjectCreate(null);
@@ -105,27 +189,17 @@ function channel(name) {
   }
 
   channel = new Channel(name);
-  channels[name] = new WeakReference(channel);
+  channel._weak = new WeakReference(channel);
+  channels[name] = channel._weak;
   return channel;
 }
 
 function subscribe(name, subscription) {
-  const chan = channel(name);
-  channels[name].incRef();
-  chan.subscribe(subscription);
+  return channel(name).subscribe(subscription);
 }
 
 function unsubscribe(name, subscription) {
-  const chan = channel(name);
-  if (!chan.unsubscribe(subscription)) {
-    return false;
-  }
-
-  channels[name].decRef();
-  if (channels[name].getRef() === 0) {
-    delete channels[name];
-  }
-  return true;
+  return channel(name).unsubscribe(subscription);
 }
 
 function hasSubscribers(name) {
@@ -139,10 +213,165 @@ function hasSubscribers(name) {
   return channel.hasSubscribers;
 }
 
+const traceEvents = [
+  'start',
+  'end',
+  'asyncStart',
+  'asyncEnd',
+  'error',
+];
+
+function assertChannel(value, name) {
+  if (!(value instanceof Channel)) {
+    throw new ERR_INVALID_ARG_TYPE(name, ['Channel'], value);
+  }
+}
+
+class TracingChannel {
+  constructor(nameOrChannels) {
+    if (typeof nameOrChannels === 'string') {
+      this.start = channel(`tracing:${nameOrChannels}:start`);
+      this.end = channel(`tracing:${nameOrChannels}:end`);
+      this.asyncStart = channel(`tracing:${nameOrChannels}:asyncStart`);
+      this.asyncEnd = channel(`tracing:${nameOrChannels}:asyncEnd`);
+      this.error = channel(`tracing:${nameOrChannels}:error`);
+    } else if (typeof nameOrChannels === 'object') {
+      const { start, end, asyncStart, asyncEnd, error } = nameOrChannels;
+
+      assertChannel(start, 'nameOrChannels.start');
+      assertChannel(end, 'nameOrChannels.end');
+      assertChannel(asyncStart, 'nameOrChannels.asyncStart');
+      assertChannel(asyncEnd, 'nameOrChannels.asyncEnd');
+      assertChannel(error, 'nameOrChannels.error');
+
+      this.start = start;
+      this.end = end;
+      this.asyncStart = asyncStart;
+      this.asyncEnd = asyncEnd;
+      this.error = error;
+    } else {
+      throw new ERR_INVALID_ARG_TYPE('nameOrChannels',
+                                     ['string', 'object', 'Channel'],
+                                     nameOrChannels);
+    }
+  }
+
+  subscribe(handlers) {
+    for (const name of traceEvents) {
+      if (!handlers[name]) continue;
+
+      this[name]?.subscribe(handlers[name]);
+    }
+  }
+
+  unsubscribe(handlers) {
+    let done = true;
+
+    for (const name of traceEvents) {
+      if (!handlers[name]) continue;
+
+      if (!this[name]?.unsubscribe(handlers[name])) {
+        done = false;
+      }
+    }
+
+    return done;
+  }
+
+  traceSync(fn, ctx = {}, thisArg, ...args) {
+    const { start, end, error } = this;
+
+    try {
+      const result = start.runStores(ctx, fn, thisArg, ...args);
+      ctx.result = result;
+      return result;
+    } catch (err) {
+      ctx.error = err;
+      error.publish(ctx);
+      throw err;
+    } finally {
+      end.publish(ctx);
+    }
+  }
+
+  tracePromise(fn, ctx = {}, thisArg, ...args) {
+    const { start, end, asyncStart, asyncEnd, error } = this;
+
+    function reject(err) {
+      ctx.error = err;
+      error.publish(ctx);
+      asyncStart.publish(ctx);
+      // TODO: Is there a way to have asyncEnd _after_ the continuation?
+      asyncEnd.publish(ctx);
+      return PromiseReject(err);
+    }
+
+    function resolve(result) {
+      ctx.result = result;
+      asyncStart.publish(ctx);
+      // TODO: Is there a way to have asyncEnd _after_ the continuation?
+      asyncEnd.publish(ctx);
+      return result;
+    }
+
+    try {
+      const promise = start.runStores(ctx, fn, thisArg, ...args);
+      return PromisePrototypeThen(promise, resolve, reject);
+    } catch (err) {
+      ctx.error = err;
+      error.publish(ctx);
+      throw err;
+    } finally {
+      end.publish(ctx);
+    }
+  }
+
+  traceCallback(fn, position = 0, ctx = {}, thisArg, ...args) {
+    const { start, end, asyncStart, asyncEnd, error } = this;
+
+    function wrappedCallback(err, res) {
+      if (err) {
+        ctx.error = err;
+        error.publish(ctx);
+      } else {
+        ctx.result = res;
+      }
+
+      asyncStart.publish(ctx);
+      try {
+        if (callback) {
+          return ReflectApply(callback, this, arguments);
+        }
+      } finally {
+        asyncEnd.publish(ctx);
+      }
+    }
+
+    const callback = ArrayPrototypeAt(args, position);
+    ArrayPrototypeSplice(args, position, 1, wrappedCallback);
+
+    try {
+      return start.runStores(ctx, fn, thisArg, ...args);
+    } catch (err) {
+      ctx.error = err;
+      error.publish(ctx);
+      throw err;
+    } finally {
+      end.publish(ctx);
+    }
+  }
+}
+
+function tracingChannel(nameOrChannels) {
+  return new TracingChannel(nameOrChannels);
+}
+
 module.exports = {
   channel,
   hasSubscribers,
   subscribe,
+  tracingChannel,
   unsubscribe,
-  Channel
+  Channel,
+  TracingChannel
 };