Feature/support atomic append

[cortex-bt]

This pr is to fix the issue/solution raised on this thread #221

[nblumhardt]

Thanks for sending this! I might be misunderstanding how the patch works, but looks like this will break the .NET 8/9 builds on other platforms by enabling atomic append, but throwing in the platform check?

Separate note, we'll also need to think about what this might mean for partially-updated applications: writers using atomic append, and writers using the OS mutex, will not coordinate. This might need some API design consideration, e.g. by keeping platform defaults in the shared: true overload of WriteTo.File(), but perhaps adding an overload that accepts a sharing model? Needs some thought. Does seem to align with having both variants of the shared file sink in the same binary, if we do that to handle the non-Windows case mentioned above.

[nblumhardt]

This should be OR rather than AND. To keep things simple, perhaps we just put OS_MUTEX in the net6.0 property group below, add a block for netstandard2.0, and remove this block?

[cortex-bt]

agreed. Have made those changes now

[nblumhardt]

This will break shared flag support on non-Windows platforms; we'd need to fall back to the OS mutex variant in the non-Windows cases.

[cortex-bt]

How about reverting back to using new FileStream in the if statement for no windows platforms. So net8/9 would work with the CreateFile method while the rest still work as before using the FileStream ?

e.g

if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
{
_fileOutput = CreateFile(
_path,
FileMode.Append,
FileSystemRights.AppendData,
FileShare.ReadWrite,
length,
FileOptions.None);
_fileStreamBufferLength = length;
}
else
{
_fileOutput = new FileStream(
_path,
FileMode.Append,
FileSystemRights.AppendData,
FileShare.ReadWrite,
length,
FileOptions.None);
}

[nblumhardt]

The OS mutex would still need to be used; the machinery around atomic append and the mutex ensure writes are not overlapping, which otherwise creates garbled logs when multiple processes share the same log file.

[cortex-bt]

so then something like this in the csproj would be more appropriate

So for windows platforms it enables ATOMIC_APPEND and for non-Windows OS_MUTEX

[nblumhardt]

CSPROJ settings like that are applied at build time, but the same packaged net8.0 and net9.0 binaries need to run on both platforms. The example above would just make the package work only for the same OS as the build server.

[cortex-bt]

Do you have any recommendations on how we could fall back to the OS mutex variant in the non-Windows cases? Or is this something that needs further planning?