events: move domain handling from events to domain

PR-URL: https://github.com/nodejs/node/pull/17403
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Andreas Madsen <amwebdk@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>

lib/domain.js

@@ -31,11 +31,6 @@ const EventEmitter = require('events');
 const errors = require('internal/errors');
 const { createHook } = require('async_hooks');
 
-// communicate with events module, but don't require that
-// module to have to load this one, since this module has
-// a few side effects.
-EventEmitter.usingDomains = true;
-
 // overwrite process.domain with a getter/setter that will allow for more
 // effective optimizations
 var _domain = [null];
@@ -387,3 +382,49 @@ Domain.prototype.bind = function(cb) {
 
   return runBound;
 };
+
+// Override EventEmitter methods to make it domain-aware.
+EventEmitter.usingDomains = true;
+
+const eventInit = EventEmitter.init;
+EventEmitter.init = function() {
+  this.domain = null;
+  if (exports.active && !(this instanceof exports.Domain)) {
+    this.domain = exports.active;
+  }
+
+  return eventInit.call(this);
+};
+
+const eventEmit = EventEmitter.prototype.emit;
+EventEmitter.prototype.emit = function emit(...args) {
+  const domain = this.domain;
+  if (domain === null || domain === undefined || this === process) {
+    return eventEmit.apply(this, args);
+  }
+
+  const type = args[0];
+  // edge case: if there is a domain and an existing non error object is given,
+  // it should not be errorized
+  // see test/parallel/test-event-emitter-no-error-provided-to-error-event.js
+  if (type === 'error' && args.length > 1 && args[1] &&
+    !(args[1] instanceof Error)) {
+    domain.emit('error', args[1]);
+    return false;
+  }
+
+  domain.enter();
+  try {
+    return eventEmit.apply(this, args);
+  } catch (er) {
+    if (typeof er === 'object' && er !== null) {
+      er.domainEmitter = this;
+      er.domain = domain;
+      er.domainThrown = false;
+    }
+    domain.emit('error', er);
+    return false;
+  } finally {
+    domain.exit();
+  }
+};

lib/events.js

@@ -21,7 +21,6 @@
 
 'use strict';
 
-var domain;
 var spliceOne;
 
 function EventEmitter() {
@@ -32,9 +31,6 @@ module.exports = EventEmitter;
 // Backwards-compat with node 0.10.x
 EventEmitter.EventEmitter = EventEmitter;
 
-EventEmitter.usingDomains = false;
-
-EventEmitter.prototype.domain = undefined;
 EventEmitter.prototype._events = undefined;
 EventEmitter.prototype._maxListeners = undefined;
 
@@ -66,14 +62,6 @@ Object.defineProperty(EventEmitter, 'defaultMaxListeners', {
 });
 
 EventEmitter.init = function() {
-  this.domain = null;
-  if (EventEmitter.usingDomains) {
-    // if there is an active domain, then attach to it.
-    domain = domain || require('domain');
-    if (domain.active && !(this instanceof domain.Domain)) {
-      this.domain = domain.active;
-    }
-  }
 
   if (this._events === undefined ||
       this._events === Object.getPrototypeOf(this)._events) {
@@ -114,47 +102,26 @@ EventEmitter.prototype.emit = function emit(type, ...args) {
   else if (!doError)
     return false;
 
-  const domain = this.domain;
-
   // If there is no 'error' event listener then throw.
   if (doError) {
     let er;
     if (args.length > 0)
       er = args[0];
-    if (domain !== null && domain !== undefined) {
-      if (!er) {
-        const errors = lazyErrors();
-        er = new errors.Error('ERR_UNHANDLED_ERROR');
-      }
-      if (typeof er === 'object' && er !== null) {
-        er.domainEmitter = this;
-        er.domain = domain;
-        er.domainThrown = false;
-      }
-      domain.emit('error', er);
-    } else if (er instanceof Error) {
+    if (er instanceof Error) {
       throw er; // Unhandled 'error' event
-    } else {
+    }
     // At least give some kind of context to the user
     const errors = lazyErrors();
     const err = new errors.Error('ERR_UNHANDLED_ERROR', er);
     err.context = er;
     throw err;
   }
-    return false;
-  }
 
   const handler = events[type];
 
   if (handler === undefined)
     return false;
 
-  let needDomainExit = false;
-  if (domain !== null && domain !== undefined && this !== process) {
-    domain.enter();
-    needDomainExit = true;
-  }
-
   if (typeof handler === 'function') {
     handler.apply(this, args);
   } else {
@@ -164,9 +131,6 @@ EventEmitter.prototype.emit = function emit(type, ...args) {
       listeners[i].apply(this, args);
   }
 
-  if (needDomainExit)
-    domain.exit();
-
   return true;
 };