Reduce allocations in ProjectState's ctor #76369
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The AsyncLazy allocations in the ProjectState ctor are accounting for 0.6% of allocations during the typing scenario in the csharp editing speedometer test. The construction of these objects can be deferred until they are queried (or copied). Local testing has about 80-90% of these lazy objects never being used, so this should save at around 0.5% of the allocations in this scenario.
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JoeRobich
approved these changes
Dec 11, 2024
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| _lazyChecksums ??= AsyncLazy.Create(static (self, cancellationToken) => self.ComputeChecksumsAsync(cancellationToken), arg: this); |
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i'm oogy on this. there's a race here where multipel threads could see null and assign a new value. I'm not 100% convinced that computing the checksum is guaranteed to produce the exact same result both times.
can you make this an interlocked CAS so only one wins?
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Sure, I can do that. I was definitely under the impression that computing the checksum would generate the same values if it happened to get unlucky and run multiple times.
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i want to believe that that would be the case... but i don't think it's proven to be true.
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OK, switched to use Interlocked.CompareExchange
…verlapping work does occur, then have both callers use the same result.
CyrusNajmabadi
approved these changes
Dec 11, 2024
This was referenced Dec 13, 2024
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The AsyncLazy allocations in the ProjectState ctor are accounting for 0.6% of allocations during the typing scenario in the csharp editing speedometer test.
The construction of these objects can be deferred until they are queried (or copied). Local testing has about 80-90% of these lazy objects never being used, so this should save at around 0.5% of the allocations in this scenario.