Re: master 2c79a8f 2/2: Use posix_spawn if possible.

[Saulius Menkevicius <sauliusmenkevicius@fastmail.com>]

Sorry I did not mention the platform, this happens on Linux/x64 and has 
been reported by multiple persons:

- https://github.com/razzmatazz/csharp-language-server/issues/12


The issue has been noticed when dotnet-based LSP servers are used with 
emacs/lsp-mode, -- in particular lsp-mode starts the server using 
`make-process` and then communicates over stdio. Link to the code that 
launches the server:

- https://github.com/emacs-lsp/lsp-mode/blob/master/lsp-mode.el#L6925


We have csharp-ls and fsac servers launched with the same mechanism as 
are for other languages -- which are working ok with posix_spawn 
enabled. It only breaks for those before-mentioned LSP servers that are 
implemented on top of dotnet and use dotnet runtime (same thing as JVM, 
but for C#/F#/CLR languages).

Now it appears, that switch to posix_spawn broke communication over 
stdio to those dotnet-based LSP servers for some technical reason, -- I 
didn't investigate yet why, because it is a bit over my head. I *think* 
there is an interplay between posix_spawn-based process launch 
implementation in emacs and dotnet runtime stdio abstractions/platform 
layer -- because otherwise other language servers work with that commit 
that enables posix_spawn, like those based on JVM too.


I know this is a bit of a corner case as posix_spawn brings performance 
benefits, but just FYI.

BR,

-Saulius Menkevicius


Am 25.01.22 um 10:41 schrieb Eli Zaretskii:
> On January 25, 2022 8:48:12 AM GMT+02:00, Saulius Menkevicius <sauliusmenkevicius@fastmail.com> wrote:
>> Hi,
>>
>> I know this has been merged a couple of months ago to `master` but I
>> would like to report breakage that occurs due to that commit.
>>
>> We have csharp-ls (C#) and fsautocomplete (F#) LSP servers that stopped
>> working with that commit (git-bisected to
>> a60053f8368e058229721f1bf1567c2b1676b239).
>>
>> I did not delve too much into the details or prepare a minimal test case
>> but this appears to be an interplay between dotnet runtime (v6) and
>> posix_spawn.
>>
>> Not sure if that warrants a revert but just a heads-up.
> Can you explain how dotnet runtime comes into play here?  Does Emacs invoke a dotnet process or something?
>
> And on what OS does this happen?