paulirwin commented on issue #1090:
URL: https://github.com/apache/lucenenet/issues/1090#issuecomment-2574368190
@NightOwl888 Actually, once I started digging into this, I'm no longer sure
about that. I think the exception is coming from here:
```c#
if (input.memoryMappedFile is null)
{
input.memoryMappedFile = MemoryMappedFile.CreateFromFile(
fileStream: fc,
mapName: null,
capacity: length,
access: MemoryMappedFileAccess.Read,
#if FEATURE_MEMORYMAPPEDFILESECURITY
memoryMappedFileSecurity: null,
#endif
inheritability: HandleInheritability.Inheritable,
leaveOpen: true); // LUCENENET: We explicitly dispose
the FileStream separately.
}
```
This is the place where `MemoryMappedFile.CreateCore` could be inlined, and
it also does the `capacity` parameter check. (The later call with the "adjust"
math ultimately calls CreateViewAccessor which does not have a capacity. I do
think we can still do what you suggest, though.) I can't currently explain the
failure, because the capacity is just set to the FileStream length, and that is
also what that method checks for internally, so they should be equal - that is,
unless the FileStream changed length somehow between the MMapIndexInput ctor
and the call to CreateFromFile... if that is true, we could pass `fc.Length`
instead of `length` as the capacity to help cut down on the likelihood of that
changing, but probably wouldn't eliminate it. Let me know if I'm missing
something on this or if you have any other ideas.
Where it throws the exception in
`MemoryMappedFile.VerifyMemoryMappedFileAccess`:
```c#
if (fileSize > capacity)
{
throw new ArgumentOutOfRangeException(nameof(capacity),
SR.ArgumentOutOfRange_CapacityGEFileSizeRequired);
}
```
https://source.dot.net/#System.IO.MemoryMappedFiles/System/IO/MemoryMappedFiles/MemoryMappedFile.Unix.cs,26
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