events: add captureRejection option

PR-URL: https://github.com/nodejs/node/pull/27867
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

1 files changed, 106 insertions, 6 deletions

diff --git a/lib/events.js b/lib/events.js
index a09333af44..ce93cd9f9b 100644
--- a/lib/events.js
+++ b/lib/events.js
@@ -23,6 +23,7 @@
 
 const {
   Array,
+  Boolean,
   MathMin,
   NumberIsNaN,
   ObjectCreate,
@@ -32,6 +33,7 @@ const {
   ReflectApply,
   ReflectOwnKeys,
 } = primordials;
+const kRejection = Symbol.for('nodejs.rejection');
 
 let spliceOne;
 
@@ -49,8 +51,10 @@ const {
   inspect
 } = require('internal/util/inspect');
 
-function EventEmitter() {
-  EventEmitter.init.call(this);
+const kCapture = Symbol('kCapture');
+
+function EventEmitter(opts) {
+  EventEmitter.init.call(this, opts);
 }
 module.exports = EventEmitter;
 module.exports.once = once;
@@ -60,6 +64,29 @@ EventEmitter.EventEmitter = EventEmitter;
 
 EventEmitter.usingDomains = false;
 
+EventEmitter.captureRejectionSymbol = kRejection;
+ObjectDefineProperty(EventEmitter, 'captureRejections', {
+  get() {
+    return EventEmitter.prototype[kCapture];
+  },
+  set(value) {
+    if (typeof value !== 'boolean') {
+      throw new ERR_INVALID_ARG_TYPE('EventEmitter.captureRejections',
+                                     'boolean', value);
+    }
+
+    EventEmitter.prototype[kCapture] = value;
+  },
+  enumerable: true
+});
+
+// The default for captureRejections is false
+ObjectDefineProperty(EventEmitter.prototype, kCapture, {
+  value: false,
+  writable: true,
+  enumerable: false
+});
+
 EventEmitter.prototype._events = undefined;
 EventEmitter.prototype._eventsCount = 0;
 EventEmitter.prototype._maxListeners = undefined;
@@ -89,7 +116,7 @@ ObjectDefineProperty(EventEmitter, 'defaultMaxListeners', {
   }
 });
 
-EventEmitter.init = function() {
+EventEmitter.init = function(opts) {
 
   if (this._events === undefined ||
       this._events === ObjectGetPrototypeOf(this)._events) {
@@ -98,8 +125,64 @@ EventEmitter.init = function() {
   }
 
   this._maxListeners = this._maxListeners || undefined;
+
+
+  if (opts && opts.captureRejections) {
+    if (typeof opts.captureRejections !== 'boolean') {
+      throw new ERR_INVALID_ARG_TYPE('options.captureRejections',
+                                     'boolean', opts.captureRejections);
+    }
+    this[kCapture] = Boolean(opts.captureRejections);
+  } else {
+    // Assigning it directly a prototype lookup, as it slighly expensive
+    // and it sits in a very sensitive hot path.
+    this[kCapture] = EventEmitter.prototype[kCapture];
+  }
 };
 
+function addCatch(that, promise, type, args) {
+  if (!that[kCapture]) {
+    return;
+  }
+
+  // Handle Promises/A+ spec, then could be a getter
+  // that throws on second use.
+  try {
+    const then = promise.then;
+
+    if (typeof then === 'function') {
+      then.call(promise, undefined, function(err) {
+        // The callback is called with nextTick to avoid a follow-up
+        // rejection from this promise.
+        process.nextTick(emitUnhandledRejectionOrErr, that, err, type, args);
+      });
+    }
+  } catch (err) {
+    that.emit('error', err);
+  }
+}
+
+function emitUnhandledRejectionOrErr(ee, err, type, args) {
+  if (typeof ee[kRejection] === 'function') {
+    ee[kRejection](err, type, ...args);
+  } else {
+    // We have to disable the capture rejections mechanism, otherwise
+    // we might end up in an infinite loop.
+    const prev = ee[kCapture];
+
+    // If the error handler throws, it is not catcheable and it
+    // will end up in 'uncaughtException'. We restore the previous
+    // value of kCapture in case the uncaughtException is present
+    // and the exception is handled.
+    try {
+      ee[kCapture] = false;
+      ee.emit('error', err);
+    } finally {
+      ee[kCapture] = prev;
+    }
+  }
+}
+
 // Obviously not all Emitters should be limited to 10. This function allows
 // that to be increased. Set to zero for unlimited.
 EventEmitter.prototype.setMaxListeners = function setMaxListeners(n) {
@@ -216,12 +299,29 @@ EventEmitter.prototype.emit = function emit(type, ...args) {
     return false;
 
   if (typeof handler === 'function') {
-    ReflectApply(handler, this, args);
+    const result = ReflectApply(handler, this, args);
+
+    // We check if result is undefined first because that
+    // is the most common case so we do not pay any perf
+    // penalty
+    if (result !== undefined && result !== null) {
+      addCatch(this, result, type, args);
+    }
   } else {
     const len = handler.length;
     const listeners = arrayClone(handler, len);
-    for (let i = 0; i < len; ++i)
-      ReflectApply(listeners[i], this, args);
+    for (var i = 0; i < len; ++i) {
+      const result = ReflectApply(listeners[i], this, args);
+
+      // We check if result is undefined first because that
+      // is the most common case so we do not pay any perf
+      // penalty.
+      // This code is duplicated because extracting it away
+      // would make it non-inlineable.
+      if (result !== undefined && result !== null) {
+        addCatch(this, result, type, args);
+      }
+    }
   }
 
   return true;