process: add deferTick

Adds a new scheduling primitive to resolve zaldo when mixing
traditional Node async programming with async/await and Promises.

We cannot "fix" nextTick without breaking the whole ecosystem.
nextTick usage should be discouraged and we should try to
incrementally move to this new primitive.

TODO:
- [] Fill in concrete examples
- [] Add tests
- [] Add benchmarks
- [] Do we need async hook logic or not?
- [] process._exiting?
- [] Anything else we are unhappy with in regard to nextTick which
     we want to fix?

Author: ronag

lib/internal/bootstrap/node.js

@@ -303,8 +303,9 @@ process.emitWarning = emitWarning;
 // bootstrap to make sure that any operation done before this are synchronous.
 // If any ticks or timers are scheduled before this they are unlikely to work.
 {
-  const { nextTick, runNextTicks } = setupTaskQueue();
+  const { nextTick, runNextTicks, deferTick } = setupTaskQueue();
   process.nextTick = nextTick;
+  process.deferTick = deferTick;
   // Used to emulate a tick manually in the JS land.
   // A better name for this function would be `runNextTicks` but
   // it has been exposed to the process object so we keep this legacy name

lib/internal/process/task_queues.js

@@ -53,6 +53,7 @@ function setHasTickScheduled(value) {
 }
 
 const queue = new FixedQueue();
+const deferQueue = new FixedQueue();
 
 // Should be in sync with RunNextTicksNative in node_task_queue.cc
 function runNextTicks() {
@@ -93,6 +94,9 @@ function processTicksAndRejections() {
       emitAfter(asyncId);
     }
     runMicrotasks();
+    while ((tock = deferQueue.shift()) !== null) {
+      tock.callback.apply(null, tock.args);
+    }
   } while (!queue.isEmpty() || processPromiseRejections());
   setHasTickScheduled(false);
   setHasRejectionToWarn(false);
@@ -133,6 +137,19 @@ function nextTick(callback) {
   queue.push(tickObject);
 }
 
+function deferTick(callback, ...args) {
+  validateFunction(callback, 'callback');
+
+  if (process._exiting)
+    return;
+
+  if (tickInfo[kHasTickScheduled] === 0) {
+    tickInfo[kHasTickScheduled] = 1;
+  }
+
+  deferQueue.push({ callback, args });
+}
+
 function runMicrotask() {
   this.runInAsyncScope(() => {
     const callback = this.callback;
@@ -166,6 +183,7 @@ module.exports = {
     setTickCallback(processTicksAndRejections);
     return {
       nextTick,
+      deferTick,
       runNextTicks,
     };
   },