René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"v24: discarded vm contexts cause OOM; possible V8 backport","articleBody":"### Version\n\nv24.21.0\n\n### Platform\n\n```text\nLinux x86_64, kernel 6.8.0-139-generic\n```\n\n### Subsystem\n\nvm, V8\n\n### What steps will reproduce the bug?\n\nSave as `repro.mjs`; run `node --max-old-space-size=128 repro.mjs`.\n\n```js\nimport { runInNewContext } from \"node:vm\";\nimport { setImmediate } from \"node:timers/promises\";\n\nconst source = `\n  globalThis.payload = new Array(1_000_000).fill(0);\n  ${Array.from({ length: 30 }, (_, index) => `\n    function work${index}(values) {\n      let result = 0;\n      for (let i = 0; i \u003c values.length; ++i) {\n        result += Math.sqrt(values[i] * values[i] + ${index});\n      }\n      return result;\n    }\n  `).join(\"\\n\")}\n  const values = [1, 2, 3, 4, 5];\n  for (let i = 0; i \u003c 1000; ++i) {\n    ${Array.from({ length: 30 }, (_, index) => `work${index}(values);`).join(\"\\n\")}\n  }\n`;\n\nfor (let i = 0; i \u003c 100; ++i) {\n  runInNewContext(source + `\\n// ${i}`);\n  await setImmediate();\n}\nconsole.log(\"Completed\");\n```\n\n### How often does it reproduce? Is there a required condition?\n\nRepeatedly on v24.15.0, v24.16.0, and v24.21.0. Completes on v22.23.2, v26.8.2, or with `--no-concurrent-recompilation` on v24.\n\n### What is the expected behavior? Why is that the expected behavior?\n\nPrint `Completed`; discarded contexts should be collectible.\n\n### What do you see instead?\n\n```\nFATAL ERROR: Reached heap limit Allocation failed - JavaScript heap out of memory\n```\n\n### Additional information\n\nThis surfaced in jsdom’s WPT runner with the default ~4 GB heap; the smaller limit makes this reproduction quick. Sampled heap retainers point through V8’s `IdentityMapBase` to realm prototypes, keeping entire windows alive.\n\nCould V8’s [“Stop collecting array and object prototypes”](https://github.com/v8/v8/commit/8901c793e4392dfea261bcbf9c679e2978847d4d) change be backported to v24? Its later [thread-safety follow-up](https://github.com/v8/v8/commit/c3553509f460b104cb8d4faf610d229a2d033f7b) might also be relevant.\n\nI haven't verified that those commits are the key ones, but it's worth trying.","author":{"url":"https://github.com/domenic","@type":"Person","name":"domenic"},"datePublished":"2026-09-16T03:36:30Z","url":"https://github.com/nodejs/node/issues/66053"}