From cb2ca234bb39d8e02b08d2866860e8d3a00b5887 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bartek=20Iwa=C5=84czuk?= <biwanczuk@gmail.com>
Date: Fri, 14 Apr 2023 02:41:32 +0200
Subject: refactor(core): limit number of boundary crossings between Rust and
 V8 (#18652)

This commit refactors "deno_core" to do fewer boundary crossings
from Rust to V8. In other words we are now calling V8 from Rust fewer
times.

This is done by merging 3 distinct callbacks into a single one. Instead
of having "op resolve" callback, "next tick" callback and "macrotask
queue" callback, we now have only "Deno.core.eventLoopTick" callback,
which is responsible for doing the same actions previous 3 callbacks.

On each of the event loop we were doing at least 2 boundary crosses
(timers macrotask queue callback and unhandled promise rejection
callback) and up to 4 crosses if there were op response and next tick
callbacks coming from Node.js compatibility layer. Now this is all done
in a single callback.

Closes https://github.com/denoland/deno/issues/18620
---
 core/01_core.js | 45 ++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 40 insertions(+), 5 deletions(-)

(limited to 'core/01_core.js')

diff --git a/core/01_core.js b/core/01_core.js
index 4cefb52e9..6231c0766 100644
--- a/core/01_core.js
+++ b/core/01_core.js
@@ -133,13 +133,48 @@
     return promiseRing[idx] != NO_PROMISE;
   }
 
-  function opresolve() {
-    for (let i = 0; i < arguments.length; i += 2) {
+  const macrotaskCallbacks = [];
+  const nextTickCallbacks = [];
+
+  function setMacrotaskCallback(cb) {
+    ArrayPrototypePush(macrotaskCallbacks, cb);
+  }
+
+  function setNextTickCallback(cb) {
+    ArrayPrototypePush(nextTickCallbacks, cb);
+  }
+
+  // This function has variable number of arguments. The last argument describes
+  // if there's a "next tick" scheduled by the Node.js compat layer. Arguments
+  // before last are alternating integers and any values that describe the
+  // responses of async ops.
+  function eventLoopTick() {
+    // First respond to all pending ops.
+    for (let i = 0; i < arguments.length - 1; i += 2) {
       const promiseId = arguments[i];
       const res = arguments[i + 1];
       const promise = getPromise(promiseId);
       promise.resolve(res);
     }
+    // Drain nextTick queue if there's a tick scheduled.
+    if (arguments[arguments.length - 1]) {
+      for (let i = 0; i < nextTickCallbacks.length; i++) {
+        nextTickCallbacks[i]();
+      }
+    } else {
+      ops.op_run_microtasks();
+    }
+    // Finally drain macrotask queue.
+    for (let i = 0; i < macrotaskCallbacks.length; i++) {
+      const cb = macrotaskCallbacks[i];
+      while (true) {
+        const res = cb();
+        ops.op_run_microtasks();
+        if (res === true) {
+          break;
+        }
+      }
+    }
   }
 
   function registerErrorClass(className, errorClass) {
@@ -406,7 +441,7 @@
     registerErrorBuilder,
     registerErrorClass,
     buildCustomError,
-    opresolve,
+    eventLoopTick,
     BadResource,
     BadResourcePrototype,
     Interrupted,
@@ -428,8 +463,8 @@
     writeSync: (rid, buffer) => ops.op_write_sync(rid, buffer),
     shutdown: opAsync.bind(null, "op_shutdown"),
     print: (msg, isErr) => ops.op_print(msg, isErr),
-    setMacrotaskCallback: (fn) => ops.op_set_macrotask_callback(fn),
-    setNextTickCallback: (fn) => ops.op_set_next_tick_callback(fn),
+    setMacrotaskCallback,
+    setNextTickCallback,
     runMicrotasks: () => ops.op_run_microtasks(),
     hasTickScheduled: () => ops.op_has_tick_scheduled(),
     setHasTickScheduled: (bool) => ops.op_set_has_tick_scheduled(bool),
-- 
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