NightOwl888 commented on code in PR #1138:
URL: https://github.com/apache/lucenenet/pull/1138#discussion_r1987719691
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src/Lucene.Net/Store/MMapDirectory.cs:
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@@ -314,7 +314,7 @@ internal virtual ByteBuffer[] Map(MMapIndexInput input,
FileStream fc, long offs
input.memoryMappedFile = MemoryMappedFile.CreateFromFile(
fileStream: fc,
mapName: null,
- capacity: length,
+ capacity: fc.Length, // use the full length of the file
Review Comment:
Lucene uses file locking to ensure that the `Map()` method is not called
during a write operation, so the `length` is consistent during this operation.
While you are correct that passing `0` is the equivalent operation as calling
`FileChannel.map()` in Java, passing the `length` should be fine. More
importantly, it has been tested very thoroughly using the `length` parameter
and we haven't had any reports of problems.
Also, since `length` is passed as a parameter to the method, we should be
using it to ensure that the end chunk is calculated using the same value. This
would fail in Java if there were a race condition here.
We could use `0` on .NET Framework and .NET Core and pass
`FileStream.Length` in all other cases, but it would require some messy
platform detection code or additional assemblies for different platforms. Using
`length` is the best way to ensure it is consistent.
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