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fix: work around setTimeout memory leak, improve wrappers (#75727)
Potential fix for a leak reported in #74855 on older node versions (see [comment](#74855 (comment))). ### Background When running middleware (or other edge functions) in `next start`, we wrap them in an edge runtime sandbox. this includes polyfills of `setTimeout` and `setInterval` which return `number` instead of `NodeJS.Timeout`. Unfortunately, on some older node versions, converting a `NodeJS.Timeout` to a number will cause that timeout to leak: nodejs/node#53335 The leaked timeout will also hold onto the callback, thus also leaking anything that was closed over (which can be a lot of things!) ### Solution Ideally, users just upgrade to a Node version that includes the fix: - [node v20.16.0](nodejs/node#53945) - [node v22.4.0](nodejs/node#53583) - node v23.0.0 But we're currently still supporting node 18, so we can't necessarily rely on that. Luckily, as noted in the description of the nodejs issue, calling `clearTimeout` seems to unleak the timeout, so we can just do that after the callback runs! ### Unrelated stuff I did While i was at it, I also fixed a (very niche) discrepancy from how `setTimeout` and `setInterval` behave on the web. when running the callback, node sets `this` to the Timeout instance: ```js > void setTimeout(function () {console.log('this in setTimeout:', this) } ) undefined > this in setTimeout: Timeout { ... } ``` but on the web, `this` is always set to `globalThis`. Our wrapper now correctly does this. ### Testing <details> <summary>Collapsed because it's long</summary> Verifying this is kinda tricky, so bear with me... Here's a script that can verify whether calling `clearTimeout` fixes the leak by using a FinalizationRegistry and triggering GC to observe whether memory leaked or not. `setTimeoutWithFix` is a simplified version of `webSetTimeoutPolyfill` from the PR. ```js // setTimeout-test.js if (typeof gc !== 'function') { console.log('this test must be run with --expose-gc') process.exit(1) } function setTimeoutWithFix(callback, ms, ...args) { const wrappedCallback = function () { try { return callback.apply(this, args) } finally { clearTimeout(timeout) } } const timeout = setTimeout(wrappedCallback, ms) return timeout } const didFinalize = {} const registry = new FinalizationRegistry((id) => { didFinalize[id] = true }) { const id = 'node setTimeout'.padEnd(26, ' ') const timeout = setTimeout(() => {}, 0) registry.register(timeout, id) didFinalize[id] = false } { const id = 'node setTimeout as number'.padEnd(26, ' ') const timeout = setTimeout(() => {}, 0) timeout[Symbol.toPrimitive]() registry.register(timeout, id) didFinalize[id] = false } { const id = 'fixed setTimeout'.padEnd(26, ' ') const timeout = setTimeoutWithFix(() => {}, 0) registry.register(timeout, id) didFinalize[id] = false } { const id = 'fixed setTimeout as number'.padEnd(26, ' ') const timeout = setTimeoutWithFix(() => {}, 0) timeout[Symbol.toPrimitive]() registry.register(timeout, id) didFinalize[id] = false } // wait for the timeouts to run void setTimeout(() => { gc() // trigger garbage collection void registry // ...but make sure we keep the registry alive // wait a task so that finalization callbacks can run setTimeout(() => console.log('did the Timeout get released after GC?', didFinalize) ) }, 10) ``` To run it, Install the required node versions: ```bash for ver in v20.15.0 v20.16.0 v22.3.0 v22.4.0 v23.0.0; do ( nvm install "$ver" ); done ``` And run the test: ```bash for ver in v20.15.0 v20.16.0 v22.3.0 v22.4.0 v23.0.0; do ( echo '-------------------' nvm use "$ver" && node --expose-gc setTimeout-test.js echo ); done ``` The output on my machine is as follows. Note that the `node setTimeout as number` case comes up as false on the older versions (because it leaks and doesn't get finalized), but `fixed setTimeout as number` (which calls `clearTimeout`) gets released fine, which is exactly what we want. ```terminal ------------------- Now using node v20.15.0 (npm v10.7.0) did the Timeout get released after GC? { 'node setTimeout ': true, 'node setTimeout as number ': false, 'fixed setTimeout ': true, 'fixed setTimeout as number': true } ------------------- Now using node v20.16.0 (npm v10.8.1) did the Timeout get released after GC? { 'node setTimeout ': true, 'node setTimeout as number ': true, 'fixed setTimeout ': true, 'fixed setTimeout as number': true } ------------------- Now using node v22.3.0 (npm v10.8.1) did the Timeout get released after GC? { 'node setTimeout ': true, 'node setTimeout as number ': false, 'fixed setTimeout ': true, 'fixed setTimeout as number': true } ------------------- Now using node v22.4.0 (npm v10.8.1) did the Timeout get released after GC? { 'node setTimeout ': true, 'node setTimeout as number ': true, 'fixed setTimeout ': true, 'fixed setTimeout as number': true } ------------------- Now using node v23.0.0 (npm v10.9.0) did the Timeout get released after GC? { 'node setTimeout ': true, 'node setTimeout as number ': true, 'fixed setTimeout ': true, 'fixed setTimeout as number': true } ``` </details>
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