In this Reddit post, FergoTheGreat examines the behavior of asynchronous file I/O in .NET on Linux, noting possible discrepancies between .NET’s async indicators and actual Linux kernel flags.

Exploring Async File I/O Behavior in .NET on Linux

Author: FergoTheGreat

The post investigates a potential discrepancy in how asynchronous file I/O is implemented or reported on Linux systems when using .NET. Specifically:

  • Async File Handle Creation in .NET: When a file handle is created with methods such as File.OpenHandle or FileStream (possibly combined with SafeFileHandle) and with either FileOptions.Asynchronous or useAsync = true, the resulting file handle in .NET reports its asynchronous capability via .IsAsync == true.

  • Linux File Descriptor Flags: However, upon further inspection using the Linux fcntl system call with F_GETFL, the handle does not show the typical Linux async flags such as O_ASYNC or O_NONBLOCK, which are indicators of asynchronous or non-blocking I/O at the OS level.

  • Observed Behavior: The resulting handle appears identical to one opened for synchronous I/O. This observation could suggest that, in practice, the underlying Linux implementation may not set kernel-level async flags, even though .NET reports async capabilities.

  • Implications: Developers relying on .NET’s async file I/O on Linux might not be truly getting kernel-accelerated asynchronous behavior, perhaps getting thread-based or emulated async semantics instead.

  • Discussion Source: The discussion was initiated in a Reddit thread by the user FergoTheGreat, raising questions for investigation or clarification by the .NET community.

References

Additional Notes

  • This question is particularly relevant for high-performance applications or those relying on true Linux async characteristics for I/O scalability.
  • Further research or official .NET documentation review may be needed to understand the complete picture.

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