diff --git a/test/common/gc.js b/test/common/gc.js new file mode 100644 index 00000000000000..af637af7bedcd6 --- /dev/null +++ b/test/common/gc.js @@ -0,0 +1,70 @@ +'use strict'; + +// TODO(joyeecheung): merge ongc.js and gcUntil from common/index.js +// into this. + +// This function can be used to check if an object factor leaks or not, +// but it needs to be used with care: +// 1. The test should be set up with an ideally small +// --max-old-space-size or --max-heap-size, which combined with +// the maxCount parameter can reproduce a leak of the objects +// created by fn(). +// 2. This works under the assumption that if *none* of the objects +// created by fn() can be garbage-collected, the test would crash due +// to OOM. +// 3. If *any* of the objects created by fn() can be garbage-collected, +// it is considered leak-free. The FinalizationRegistry is used to +// terminate the test early once we detect any of the object is +// garbage-collected to make the test less prone to false positives. +// This may be especially important for memory management relying on +// emphemeron GC which can be inefficient to deal with extremely fast +// heap growth. +// Note that this can still produce false positives. When the test using +// this function still crashes due to OOM, inspect the heap to confirm +// if a leak is present (e.g. using heap snapshots). +// The generateSnapshotAt parameter can be used to specify a count +// interval to create the heap snapshot which may enforce a more thorough GC. +// This can be tried for code paths that require it for the GC to catch up +// with heap growth. However this type of forced GC can be in conflict with +// other logic in V8 such as bytecode aging, and it can slow down the test +// significantly, so it should be used scarcely and only as a last resort. +async function checkIfCollectable( + fn, maxCount = 4096, generateSnapshotAt = Infinity, logEvery = 128) { + let anyFinalized = false; + let count = 0; + + const f = new FinalizationRegistry(() => { + anyFinalized = true; + }); + + async function createObject() { + const obj = await fn(); + f.register(obj); + if (count++ < maxCount && !anyFinalized) { + setImmediate(createObject, 1); + } + // This can force a more thorough GC, but can slow the test down + // significantly in a big heap. Use it with care. + if (count % generateSnapshotAt === 0) { + // XXX(joyeecheung): This itself can consume a bit of JS heap memory, + // but the other alternative writeHeapSnapshot can run into disk space + // not enough problems in the CI & be slower depending on file system. + // Just do this for now as long as it works and only invent some + // internal voodoo when we absolutely have no other choice. + require('v8').getHeapSnapshot().pause().read(); + console.log(`Generated heap snapshot at ${count}`); + } + if (count % logEvery === 0) { + console.log(`Created ${count} objects`); + } + if (anyFinalized) { + console.log(`Found finalized object at ${count}, stop testing`); + } + } + + createObject(); +} + +module.exports = { + checkIfCollectable, +};