Use v8.serialize when available. #5565
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very cool |
Codecov Report
@@ Coverage Diff @@
## master #5565 +/- ##
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+ Coverage 61.67% 61.75% +0.08%
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Files 213 213
Lines 7160 7165 +5
Branches 4 4
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+ Hits 4416 4425 +9
+ Misses 2743 2739 -4
Partials 1 1
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packages/jest-haste-map/src/index.js
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| if (version !== process.versions.v8) { | ||
| throw new Error('jest-haste-map: v8 versions do not match.'); | ||
| } | ||
| return hasteMap; |
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Setting null prototype is not necessary with v8.deserialize?
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Ah, that doesn't meet my expectation:
v8.deserialize(v8.serialize(Object.create(null))).__proto__ === Object.create(null).__proto__ // false
fix incoming
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Anyway, would be nice to extract this to a helper/module one day :) |
| fs.readFileSync(this._cachePath), | ||
| ); | ||
| if (version !== process.versions.v8) { | ||
| throw new Error('jest-haste-map: v8 versions do not match.'); |
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We should be smarter here, like purging the cache and keep it going, but for the moment it's OK.
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It does already do that. Exceptions from this function are caught in the parent and a new map is created which will overwrite this one. For all intents and purposes, this error message is not user visible at this time.
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@thymikee Yes, we've got to work on that soon; there are other parts where we could hugely benefit from this, like Exciting times ahead! |
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This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs. |
Summary
v8 (in Node 8+) has a new function called
v8.serializewhich can be used to encode/decode JavaScript data structures faster than JSON. This diff changesjest-haste-mapto use the new function in newer versions of Node and falls back to JSON if the serializer/deserializer aren't available. It also does a v8 version check to ensure we aren't trying to read a possible outdated binary blob. Making the cache work across node versions is a non goal and will be broken by this feature. If a user upgrades node, the function will throw and recreate the haste map.I benchmarked this on a 73mb haste map and got the following results averaged over 10 runs:
Reading is ~200ms faster and writing is 500ms faster. I suspect this is because of less validation work and less GC (edit: it's not GC). Since during startup we read the haste map once, write updates and then read it once per worker, this means that on a gigantic repo, this saves 500+200+(200*workers) time, or close to a second of actual time. On most repos out there in the world, there is likely no visible performance difference.
Next steps (up for grabs):
jest-serializepackage that uses either v8 serialize or JSON.jest-serializeacross Jest (jest-worker,jest-haste-map) and Metro.Test plan
I updated some of the tests to pass on either node 8+ or node versions below that.