process: make tick callback and promise rejection callback more robust

- Rename `internalTickCallback` to `processTicksAndRejections`, make
  sure it does not get called if it's not set in C++.
- Rename `emitPromiseRejectionWarnings` to `processPromiseRejections`
  since it also emit events that are not warnings.
- Sets `SetPromiseRejectCallback` in the `Environment` constructor
  to make sure it only gets called once per-isolate, and make
  sure it does not get called if it's not set in C++.
- Wrap promise rejection callback initialization into
  `listenForRejections()`.
- Add comments.

PR-URL: https://github.com/nodejs/node/pull/25200
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>

2 files changed, 20 insertions, 15 deletions

diff --git a/lib/internal/process/next_tick.js b/lib/internal/process/next_tick.js
index 0bfe168975..24104ec34a 100644
--- a/lib/internal/process/next_tick.js
+++ b/lib/internal/process/next_tick.js
@@ -6,15 +6,14 @@ const {
   tickInfo,
   // Used to run V8's micro task queue.
   runMicrotasks,
-  setTickCallback,
-  initializePromiseRejectCallback
+  setTickCallback
 } = internalBinding('task_queue');
 
 const {
   setHasRejectionToWarn,
   hasRejectionToWarn,
-  promiseRejectHandler,
-  emitPromiseRejectionWarnings
+  listenForRejections,
+  processPromiseRejections
 } = require('internal/process/promises');
 
 const {
@@ -49,10 +48,10 @@ function runNextTicks() {
   if (!hasTickScheduled() && !hasRejectionToWarn())
     return;
 
-  internalTickCallback();
+  processTicksAndRejections();
 }
 
-function internalTickCallback() {
+function processTicksAndRejections() {
   let tock;
   do {
     while (tock = queue.shift()) {
@@ -80,7 +79,7 @@ function internalTickCallback() {
     }
     setHasTickScheduled(false);
     runMicrotasks();
-  } while (!queue.isEmpty() || emitPromiseRejectionWarnings());
+  } while (!queue.isEmpty() || processPromiseRejections());
   setHasRejectionToWarn(false);
 }
 
@@ -134,11 +133,10 @@ function nextTick(callback) {
 // TODO(joyeecheung): make this a factory class so that node.js can
 // control the side effects caused by the initializers.
 exports.setup = function() {
-  // Initializes the per-isolate promise rejection callback which
-  // will call the handler being passed into this function.
-  initializePromiseRejectCallback(promiseRejectHandler);
+  // Sets the per-isolate promise rejection callback
+  listenForRejections();
   // Sets the callback to be run in every tick.
-  setTickCallback(internalTickCallback);
+  setTickCallback(processTicksAndRejections);
   return {
     nextTick,
     runNextTicks
diff --git a/lib/internal/process/promises.js b/lib/internal/process/promises.js
index 047a9d43aa..f3e118e2ce 100644
--- a/lib/internal/process/promises.js
+++ b/lib/internal/process/promises.js
@@ -8,7 +8,8 @@ const {
     kPromiseHandlerAddedAfterReject,
     kPromiseResolveAfterResolved,
     kPromiseRejectAfterResolved
-  }
+  },
+  setPromiseRejectCallback
 } = internalBinding('task_queue');
 
 // *Must* match Environment::TickInfo::Fields in src/env.h.
@@ -117,7 +118,9 @@ function emitDeprecationWarning() {
   }
 }
 
-function emitPromiseRejectionWarnings() {
+// If this method returns true, at least one more tick need to be
+// scheduled to process any potential pending rejections
+function processPromiseRejections() {
   while (asyncHandledRejections.length > 0) {
     const { promise, warning } = asyncHandledRejections.shift();
     if (!process.emit('rejectionHandled', promise)) {
@@ -142,9 +145,13 @@ function emitPromiseRejectionWarnings() {
   return maybeScheduledTicks || pendingUnhandledRejections.length !== 0;
 }
 
+function listenForRejections() {
+  setPromiseRejectCallback(promiseRejectHandler);
+}
+
 module.exports = {
   hasRejectionToWarn,
   setHasRejectionToWarn,
-  promiseRejectHandler,
-  emitPromiseRejectionWarnings
+  listenForRejections,
+  processPromiseRejections
 };