Can someone explain how select/poll/epoll interacts with C# code in socket Select() or SocketAsyncEventArgs?

[cjmld5]

Can someone explain how select/poll/epoll interacts with C# code in socket Select() or SocketAsyncEventArgs?
below example:

Socket.Select() 
-> UnsafeNclNativeMethods.OSSOCK.select(0, array, array2, array3, ref socketTime)
-> [DllImport("ws2_32.dll", SetLastError = true)]
     internal static extern int select([In] int ignoredParameter, [In][Out] IntPtr[] readfds, [In][Out] IntPtr[] writefds, [In][Out] IntPtr[] exceptfds, [In] ref TimeValue timeout)

and how winsock2 interacts with dotnet runtime?it seems in C++ we could add a head
#include<winsock2.h>
and see select code below:

#if INCL_WINSOCK_API_PROTOTYPES
WINSOCK_API_LINKAGE
int
WSAAPI
select(
    _In_ int nfds,
    _Inout_opt_ fd_set FAR * readfds,
    _Inout_opt_ fd_set FAR * writefds,
    _Inout_opt_ fd_set FAR * exceptfds,
    _In_opt_ const struct timeval FAR * timeout
    );
#endif /* INCL_WINSOCK_API_PROTOTYPES */

and here could not find some relations to interacts with dotnet runtime pal_networking.c？How should they be strung together？

[huoyaoyuan]

@dotnet/ncl

[wfurt]

That really depends on how the socket is used from c# @cjmld5. For example, you can use synchronous read and write and neither one would be used. You can use Socket.Select or Socket.Poll and that would translate pretty much directly to OS calls. The epoll comes in picture when Async methods are used. In ideal case, I would suggest not to mix sync & async - pick one and stick to it.

[cjmld5]

yes，this should not be a better practice that mix usage of sync & async. it seems that it is a knowledge blind spot for me on how Socket.Select or Socket.Poll translate to OS calls：Socket.Select gose to winsock2 and how winsock2 go to ws2_32.dll`s select method, and how winsock2 goes to https://github.com/dotnet/runtime/blob/main/src/libraries/Common/src/Interop/Windows/WinSock/Interop.select.cs or other platform *.cs

[ManickaP]

About the select and diff between *NIX and Win: on Windows we p/invoke directly into system libraries without the native shims (pal_networking.c): https://github.com/dotnet/runtime/blob/main/src/libraries/Common/src/Interop/Windows/WinSock/Interop.select.cs since Windows has stable APIs.

I hope this helps a bit.

[cjmld5]

could u explain more about "we p/invoke directly into system libraries without the native shims" like how select Eventually goes to "Interop.select.cs"？