Reduce allocations in PollingWildCardChangeToken #116175
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Pull Request Overview
This PR aims to reduce allocations in PollingWildCardChangeToken by modifying how timestamps and hash computations are handled.
- Changed _lastScanTimeUtc from a nullable DateTime to a non-nullable DateTime with a Ticks check as a sentinel value.
- Optimized ComputeHash by using MemoryMarshal for zero-allocation conversions in the NET build.
- Updated hash assignment logic and simplified the HasChanged property.
Comments suppressed due to low confidence (3)
src/libraries/Microsoft.Extensions.FileProviders.Physical/src/PollingWildCardChangeToken.cs:141
- Using the conditional assignment (??=) here means that once _previousHash is set, it will never update even if file contents change. Please verify that this behavior is intended for correct change tracking.
_previousHash ??= currentHash;
src/libraries/Microsoft.Extensions.FileProviders.Physical/src/PollingWildCardChangeToken.cs:179
- Ensure that using MemoryMarshal.AsBytes on an array containing lastChangedUtc produces a consistent byte representation compared to using BinaryPrimitives.WriteInt64LittleEndian in the non-NET branch.
sha256.AppendData(MemoryMarshal.AsBytes([lastChangedUtc]));
src/libraries/Microsoft.Extensions.FileProviders.Physical/src/PollingWildCardChangeToken.cs:125
- [nitpick] Using _lastScanTimeUtc.Ticks != 0 as a sentinel for uninitialized state is clear, but please confirm that treating DateTime.MinValue as an appropriate default works correctly with all expected file timestamps.
if (_lastScanTimeUtc.Ticks != 0 && _lastScanTimeUtc < lastWriteTimeUtc)
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jkotas
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Inspired by this comment: #116111 (comment)