ptr_test.cc

// g++ ptr_test.cc --shared -o ptr_test.so
#include <cstdint>

static uint32_t g_p = 0;

extern "C" {

void* gen_ptr() {
  return (void*)&g_p;
}

void digest_ptr(void* p) {
  (*(uint32_t*)p) ++;
}

}

toArrayBuffer_bench.js

import * as ffi from "bun:ffi"
const link = ffi.dlopen("ptr_test.so", {
  gen_ptr: {
    returns: ffi.FFIType.ptr
  },
  digest_ptr: {
    args: [ffi.FFIType.ptr]
  }
})
const lib = link.symbols

function withToArrayBuffer() {
  const p = lib.gen_ptr();
  const a = ffi.toArrayBuffer(p, 0, 1);
  lib.digest_ptr(ffi.ptr(a));
}

function withoutToArrayBuffer() {
  const p = lib.gen_ptr();
  lib.digest_ptr(p);
}

for (let i = 0; i < 100000; ++i) {
  withToArrayBuffer();
  withoutToArrayBuffer();
}

const iters = 10000000;

{
  const t0 = performance.now();
  for (let i = 0; i < iters; ++i) {
    withToArrayBuffer();
  }
  const t1 = performance.now();
  console.log("toArrayBuffer", (t1-t0) * 1e6 / iters, "ns/iter");
}

{
  const t0 = performance.now();
  for (let i = 0; i < iters; ++i) {
    withoutToArrayBuffer();
  }
  const t1 = performance.now();
  console.log("Without toArrayBuffer", (t1-t0) * 1e6 / iters, "ns/iter");
}

On a canary build, this is the output:

toArrayBuffer 135.7197583 ns/iter
Without toArrayBuffer 34.2141875 ns/iter