René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"ffi: getFunction() and the functions accessor rebuild wrappers on every call","articleBody":"### Version\n\nmain\n\n### Platform\n\n```text\nLinux\n```\n\n### Subsystem\n\nffi\n\n### What steps will reproduce the bug?\n\n`repro.c`\n```c\n#include \u003cstdint.h>\n\nint32_t add2(int32_t a, int32_t b) {\n  return a + b;\n}\n```\n\n`repro.js`\n```js\nimport { DynamicLibrary, suffix } from 'node:ffi';\nimport { stat } from 'node:fs/promises';\n\nconst libPath = new URL(`./repro.${suffix}`, import.meta.url).pathname;\nawait stat(libPath);\n\nconst lib = new DynamicLibrary(libPath);\nlib.getFunction('add2', { arguments: ['i32', 'i32'], return: 'i32' });\n\nconsole.log('same wrapper on two reads:', lib.functions.add2 === lib.functions.add2);\n\n// Idiomatic call through the accessor, which re-resolves on every iteration.\nconst before = process.memoryUsage.rss();\nlet sum = 0;\nfor (let i = 0; i \u003c 20000; i++) sum += lib.functions.add2(20, 22);\nconst after = process.memoryUsage.rss();\n\nconsole.log(`sum: ${sum}`);\nconsole.log(`rss growth: ${((after - before) / 1024 / 1024).toFixed(1)} MiB`);\n\nlib.close();\n```\n\nCommands to run:\n```console\n$ cc -shared -fPIC -O2 -o repro.so repro.c\n\n$ node --experimental-ffi repro.js\n```\n\n### How often does it reproduce? Is there a required condition?\n\nAlways\n\n### What is the expected behavior? Why is that the expected behavior?\n\nReading an already-resolved function off `library.functions` returns the same wrapper each time, and calling through the accessor in a loop does not grow memory.\n\n### What do you see instead?\n\n```console\nsame wrapper on two reads: false\nsum: 840000\nrss growth: 56.0 MiB\n```\n\nEach read builds a new wrapper, so `lib.functions.add2 !== lib.functions.add2`, and the loop allocates a fresh trampoline page plus a new `FFIFunctionInfo` per iteration, holding all of them until GC.\n\n\n\n### Additional information\n\n_No response_","author":{"url":"https://github.com/trivikr","@type":"Person","name":"trivikr"},"datePublished":"2026-08-02T23:10:50Z","url":"https://github.com/nodejs/node/issues/64970"}