From 9fb161c3f4fdb3e503ca4250a25b8dde6d838efa Mon Sep 17 00:00:00 2001
From: Rich Trott <rtrott@gmail.com>
Date: Wed, 22 Apr 2020 16:25:11 -0700
Subject: [PATCH] fixup! domain: allow concurrent user-land impl

---
 lib/domain.js | 101 +++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 100 insertions(+), 1 deletion(-)

diff --git a/lib/domain.js b/lib/domain.js
index f4cb9ce7db5907..83d2e9be7f53f6 100644
--- a/lib/domain.js
+++ b/lib/domain.js
@@ -36,6 +36,7 @@ const {
 } = primordials;
 
 const EventEmitter = require('events');
+const { ERR_UNHANDLED_ERROR } = require('internal/errors').codes;
 const { createHook } = require('async_hooks');
 const { useDomainTrampoline } = require('internal/async_hooks');
 
@@ -128,7 +129,7 @@ function topLevelDomainCallback(cb, ...args) {
 
 // It's possible to enter one domain while already inside another one. The stack
 // is each entered domain.
-const stack = process._domainStack;
+let stack = [];
 exports._stack = stack;
 useDomainTrampoline(topLevelDomainCallback);
 
@@ -438,3 +439,101 @@ 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() {
+  ObjectDefineProperty(this, 'domain', {
+    configurable: true,
+    enumerable: false,
+    value: null,
+    writable: true
+  });
+  if (exports.active && !(this instanceof exports.Domain)) {
+    this.domain = exports.active;
+  }
+
+  return eventInit.call(this);
+};
+
+const eventEmit = EventEmitter.prototype.emit;
+EventEmitter.prototype.emit = function(...args) {
+  const domain = this.domain;
+
+  const type = args[0];
+  const shouldEmitError = type === 'error' &&
+                          this.listenerCount(type) > 0;
+
+  // Just call original `emit` if current EE instance has `error`
+  // handler, there's no active domain or this is process
+  if (shouldEmitError || domain === null || domain === undefined ||
+      this === process) {
+    return ReflectApply(eventEmit, this, args);
+  }
+
+  if (type === 'error') {
+    const er = args.length > 1 && args[1] ?
+      args[1] : new ERR_UNHANDLED_ERROR();
+
+    if (typeof er === 'object') {
+      er.domainEmitter = this;
+      ObjectDefineProperty(er, 'domain', {
+        configurable: true,
+        enumerable: false,
+        value: domain,
+        writable: true
+      });
+      er.domainThrown = false;
+    }
+
+    // Remove the current domain (and its duplicates) from the domains stack and
+    // set the active domain to its parent (if any) so that the domain's error
+    // handler doesn't run in its own context. This prevents any event emitter
+    // created or any exception thrown in that error handler from recursively
+    // executing that error handler.
+    const origDomainsStack = stack.slice();
+    const origActiveDomain = process.domain;
+
+    // Travel the domains stack from top to bottom to find the first domain
+    // instance that is not a duplicate of the current active domain.
+    let idx = stack.length - 1;
+    while (idx > -1 && process.domain === stack[idx]) {
+      --idx;
+    }
+
+    // Change the stack to not contain the current active domain, and only the
+    // domains above it on the stack.
+    if (idx < 0) {
+      stack.length = 0;
+    } else {
+      stack.splice(idx + 1);
+    }
+
+    // Change the current active domain
+    if (stack.length > 0) {
+      exports.active = process.domain = stack[stack.length - 1];
+    } else {
+      exports.active = process.domain = null;
+    }
+
+    updateExceptionCapture();
+
+    domain.emit('error', er);
+
+    // Now that the domain's error handler has completed, restore the domains
+    // stack and the active domain to their original values.
+    exports._stack = stack = origDomainsStack;
+    exports.active = process.domain = origActiveDomain;
+    updateExceptionCapture();
+
+    return false;
+  }
+
+  domain.enter();
+  const ret = ReflectApply(eventEmit, this, args);
+  domain.exit();
+
+  return ret;
+};