perf: resolve `Promise`s natively for async ops #1163

CyanChanges · 2025-07-20T15:51:08Z

Supersede #1158

Waiting for

~~Missing binding for Exception::CaptureStackTrace rusty_v8#1818~~
waiting for for deno_core updates to the latest rusty_v8

Summary

22% more performant async ops,
(by resolve Promises natively)
and less memory usage (no need of preparing an array of results)

const ops = Deno.core.ops;
// ops.op_print(Object.keys(ops).join('\n')+'\n')
function tImm(tag, p) {
  const symbol = Symbol('k.notImm')
  function check(v) {
    const imm = v !== symbol
    // ops.op_print(`@${tag} ${imm}\n`)
  }
  const p1 = Promise.any([p, Promise.resolve(symbol)])
  p1.then(check, check)
}
for (let i = 0; i < 50000; i++) {
tImm("op_void_async", ops.op_void_async())
tImm("op_void_async_deferred", ops.op_void_async_deferred())
tImm("op_error_async", ops.op_error_async())
}
// ops.op_print("Hello World\n")

CyanChanges · 2025-07-20T16:01:07Z

Help wanted

async stacktrace for error is gone rn

I need do the same but in native:

somewhat solution: (obviously bad, but at least it kinda works)

Don't have a bindings for this, also this is private i guess (https://github.com/v8/v8/blob/e3529d092163dcfbbb454257dc4103bdebfeda48/src/execution/messages.h#L150

This one should be public?, but still no binding for it i guess: https://github.com/v8/v8/blob/e3529d092163dcfbbb454257dc4103bdebfeda48/include/v8-exception.h#L69

I didn't found a considerable solutions, maybe I need to add bindings to rusty_v8 first?
UPDATE: denoland/rusty_v8#1818

core/01_core.js

bartlomieju · 2025-08-04T15:28:06Z

core/01_core.js

    op_unref_op(promiseId);
  }

  function refOpPromise(promise) {


Note to self, verify purpose of refOp and refOpPromise and if they can be de-duped

Since promiseId is now private so it's not able to be retrieved in JS side directly so I add ops for ref/unref promises directly

bartlomieju · 2025-08-04T15:31:18Z

core/runtime/op_driver/futures_unordered_driver.rs

+    self.promises.borrow().get(promise_id as usize).is_some()
+  }
+
+  fn _get_promise<'s>(


Note to self, remove if not needed before landing

bartlomieju · 2025-08-04T15:37:03Z

core/runtime/op_driver/futures_unordered_driver.rs

      queue,
      completed_waker,
      arena: Default::default(),
+      promises: Default::default(),


This needs to be pre-allocated

bartlomieju · 2025-08-04T15:46:28Z

@CyanChanges can you please provide result when running this code in your PR and on main?

// bench.js
const ops = Deno.core.ops;
// ops.op_print(Object.keys(ops).join('\n')+'\n')

async function bench(name, op) {
  const start = new Date();
  for (let i = 0; i < 500000; i++) {
    await op();
  }
  const end = new Date();
  const duration = end - start;
  ops.op_print(`${name} took ${duration}ms\n`);
}

await bench("op_void_async", ops.op_void_async)
await bench("op_void_async_deferred", ops.op_void_async_deferred)

target/release/dcore bench.js

// bench_batched.js
const ops = Deno.core.ops;
// ops.op_print(Object.keys(ops).join('\n')+'\n')

async function bench(name, op) {
  const start = new Date();
  const batched = new Array(500000).fill(op);
  await Promise.all(batched.map((fn) => fn()));
  const end = new Date();
  const duration = end - start;
  ops.op_print(`${name} took ${duration}ms\n`);
}

await bench("op_void_async", ops.op_void_async)
await bench("op_void_async_deferred", ops.op_void_async_deferred)

target/release/dcore bench_batched.js

From our benchmarks this PR appears to be significantly slower than main:

// this PR
target/release/dcore bench.js
🛑 deno_core binary is meant for development and testing purposes.
Run bench.js
op_void_async took 198ms
op_void_async_deferred took 1166ms

// main

./dcore_main bench.js                                                           [INS]
🛑 deno_core binary is meant for development and testing purposes.
Run bench.js
op_void_async took 35ms
op_void_async_deferred took 974ms

CyanChanges · 2025-08-04T16:11:51Z

@CyanChanges can you please provide result when running this code in your PR and on main?

// bench.js
const ops = Deno.core.ops;
// ops.op_print(Object.keys(ops).join('\n')+'\n')

async function bench(name, op) {
  const start = new Date();
  for (let i = 0; i < 500000; i++) {
    await op();
  }
  const end = new Date();
  const duration = end - start;
  ops.op_print(`${name} took ${duration}ms\n`);
}

await bench("op_void_async", ops.op_void_async)
await bench("op_void_async_deferred", ops.op_void_async_deferred)

target/release/dcore bench.js

// bench_batched.js
const ops = Deno.core.ops;
// ops.op_print(Object.keys(ops).join('\n')+'\n')

async function bench(name, op) {
  const start = new Date();
  const batched = new Array(500000).fill(op);
  await Promise.all(batched.map((fn) => fn()));
  const end = new Date();
  const duration = end - start;
  ops.op_print(`${name} took ${duration}ms\n`);
}

await bench("op_void_async", ops.op_void_async)
await bench("op_void_async_deferred", ops.op_void_async_deferred)

target/release/dcore bench_batched.js

From our benchmarks this PR appears to be significantly slower than main:

// this PR
target/release/dcore bench.js
🛑 deno_core binary is meant for development and testing purposes.
Run bench.js
op_void_async took 198ms
op_void_async_deferred took 1166ms

// main

./dcore_main bench.js                                                           [INS]
🛑 deno_core binary is meant for development and testing purposes.
Run bench.js
op_void_async took 35ms
op_void_async_deferred took 974ms

@CyanChanges can you please provide result when running this code in your PR and on main?

// bench.js
const ops = Deno.core.ops;
// ops.op_print(Object.keys(ops).join('\n')+'\n')

async function bench(name, op) {
  const start = new Date();
  for (let i = 0; i < 500000; i++) {
    await op();
  }
  const end = new Date();
  const duration = end - start;
  ops.op_print(`${name} took ${duration}ms\n`);
}

await bench("op_void_async", ops.op_void_async)
await bench("op_void_async_deferred", ops.op_void_async_deferred)

target/release/dcore bench.js

// bench_batched.js
const ops = Deno.core.ops;
// ops.op_print(Object.keys(ops).join('\n')+'\n')

async function bench(name, op) {
  const start = new Date();
  const batched = new Array(500000).fill(op);
  await Promise.all(batched.map((fn) => fn()));
  const end = new Date();
  const duration = end - start;
  ops.op_print(`${name} took ${duration}ms\n`);
}

await bench("op_void_async", ops.op_void_async)
await bench("op_void_async_deferred", ops.op_void_async_deferred)

target/release/dcore bench_batched.js

From our benchmarks this PR appears to be significantly slower than main:

// this PR
target/release/dcore bench.js
🛑 deno_core binary is meant for development and testing purposes.
Run bench.js
op_void_async took 198ms
op_void_async_deferred took 1166ms

// main

./dcore_main bench.js                                                           [INS]
🛑 deno_core binary is meant for development and testing purposes.
Run bench.js
op_void_async took 35ms
op_void_async_deferred took 974ms

I just switched to NixOS recently, so I needs to configure the dev environment and rebuild it. It may take a while tho

CyanChanges · 2025-08-04T16:16:58Z

@CyanChanges can you please provide result when running this code in your PR and on main?

// bench.js
const ops = Deno.core.ops;
// ops.op_print(Object.keys(ops).join('\n')+'\n')

async function bench(name, op) {
  const start = new Date();
  for (let i = 0; i < 500000; i++) {
    await op();
  }
  const end = new Date();
  const duration = end - start;
  ops.op_print(`${name} took ${duration}ms\n`);
}

await bench("op_void_async", ops.op_void_async)
await bench("op_void_async_deferred", ops.op_void_async_deferred)

target/release/dcore bench.js

// bench_batched.js
const ops = Deno.core.ops;
// ops.op_print(Object.keys(ops).join('\n')+'\n')

async function bench(name, op) {
  const start = new Date();
  const batched = new Array(500000).fill(op);
  await Promise.all(batched.map((fn) => fn()));
  const end = new Date();
  const duration = end - start;
  ops.op_print(`${name} took ${duration}ms\n`);
}

await bench("op_void_async", ops.op_void_async)
await bench("op_void_async_deferred", ops.op_void_async_deferred)

target/release/dcore bench_batched.js

From our benchmarks this PR appears to be significantly slower than main:

// this PR
target/release/dcore bench.js
🛑 deno_core binary is meant for development and testing purposes.
Run bench.js
op_void_async took 198ms
op_void_async_deferred took 1166ms

// main

./dcore_main bench.js                                                           [INS]
🛑 deno_core binary is meant for development and testing purposes.
Run bench.js
op_void_async took 35ms
op_void_async_deferred took 974ms

CyanChanges · 2025-08-04T16:20:55Z

Yeah seems the improvements of the PR are mainly from `op_error_async`

littledivy

I tried using internalized strings and re-using the v8::Private. It cuts down some overhead but still not as fast as main:

diff --git a/core/runtime/op_driver/mod.rs b/core/runtime/op_driver/mod.rs
index 4a9eaa8..fe66a8f 100644
--- a/core/runtime/op_driver/mod.rs
+++ b/core/runtime/op_driver/mod.rs
@@ -21,7 +21,6 @@ pub use self::op_results::OpResult;
 use self::op_results::PendingOpInfo;
 pub use self::op_results::V8OpMappingContext;
 pub use self::op_results::V8RetValMapper;
-use crate::runtime::v8_static_strings::INTERNAL_PROMISE_ID;

 #[derive(Default)]
 /// Returns a set of stats on inflight ops.
@@ -37,6 +36,10 @@ pub enum OpScheduling {
   Deferred,
 }

+thread_local! {
+static PRIVATE_PROMISE_ID: std::cell::OnceCell<v8::Global<v8::Private>> = std::cell::OnceCell::new();
+}
+
 /// `OpDriver` encapsulates the interface for handling operations within Deno's runtime.
 ///
 /// This trait defines methods for submitting ops and polling readiness inside of the
@@ -55,8 +58,21 @@ pub(crate) trait OpDriver<C: OpMappingContext = V8OpMappingContext>:
     &self,
     scope: &mut v8::HandleScope<'s>,
   ) -> v8::Local<'s, v8::Private> {
-    let name = INTERNAL_PROMISE_ID.v8_string(scope).unwrap();
-    v8::Private::for_api(scope, Some(name))
+    PRIVATE_PROMISE_ID.with(move |cell| {
+      let global = cell.get_or_init(|| {
+        let internalized = v8::String::new_from_one_byte(
+          scope,
+          b"a",
+          v8::NewStringType::Internalized,
+        )
+        .unwrap();
+
+        let private = v8::Private::for_api(scope, Some(internalized));
+        v8::Global::new(scope, private)
+      });
+
+      v8::Local::new(scope, global)
+    })
   }

   fn _get_promise<'s>(
diff --git a/core/runtime/v8_static_strings.rs b/core/runtime/v8_static_strings.rs
index 1bee095..c5c0528 100644
--- a/core/runtime/v8_static_strings.rs
+++ b/core/runtime/v8_static_strings.rs
@@ -33,7 +33,6 @@ v8_static_strings!(
   NAME = "name",
   OPS = "ops",
   RESOLVE = "resolve",
-  INTERNAL_PROMISE_ID = "Promise#Deno.core.internalPromiseId",
   STACK = "stack",
   URL = "url",
   WASM_INSTANCE = "WasmInstance",

$ ./dcore_main test.mjs                                                  [INS]
🛑 deno_core binary is meant for development and testing purposes.
Run test.mjs
op_void_async took 45ms
op_void_async_deferred took 1270ms
$ target/release/dcore test.mjs                                           [INS]
🛑 deno_core binary is meant for development and testing purposes.
Run test.mjs
op_void_async took 174ms
op_void_async_deferred took 1394ms

perf: resolve Promises natively for async ops

43af50c

This was referenced Jul 20, 2025

perf: faster timer #1164

Draft

perf: optimize event_loop_tick and async ops #1158

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format

eef350b

bartlomieju reviewed Aug 4, 2025

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bartlomieju reviewed Aug 4, 2025

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CyanChanges added 2 commits August 4, 2025 23:32

remove debug print

6caca38

Merge branch 'main' into native-async-ops

86cdf4c

bartlomieju reviewed Aug 4, 2025

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littledivy reviewed Aug 6, 2025

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