the real problem is not that fstat and ftell lock the CRT

I agree with that, but rather than pointing the finger at accept(), (which (assumption!) locks the underlying file descriptor as it will be modified by when the call completes), but rather at the PerlIO that calls f*() calls on sockets.

I guess you could also blame the CRT for locking the file descriptors before checking whether they are valid handles for the operation to be performed.

Is it possible to recode accept to avoid the CRT?

On a cursory inspection I don't think so. accept() is just redined as win32_accept(), and that essentially just calls the CRT accept():

SOCKET
win32_accept(SOCKET s, struct sockaddr *addr, int *addrlen)
{
    SOCKET r;

    SOCKET_TEST((r = accept(TO_SOCKET(s), addr, addrlen)), INVALID_SOC
+KET);
    return OPEN_SOCKET(r);
}
[download]

I don't have access to the MSCRT sources, (I think you can pay for such access?), but from my point of view it's an opaque box. And probably should be.

In the end, like so many others, the root of this problem lies in the difficulty of trying to make a non-POSIX OS act like POSIX. It's amazing that as much works as does.

Personally, I would assume that the VC CRT then calls the appropriate Winsock functions, which would be accept as imported from winsock.h. Maybe looking at whatever CRT/call sequence mingw uses could help, even if it moves Perl towards bringing its own OS to the table...

Maybe looking at whatever CRT/call sequence mingw uses could help,

They almost certainly call accept(), which is probably what is being called now.

But I don't think changing the accept() call is the right way to address problems in PerlIO. The former currently works, it's the latter that has problems.

even if it moves Perl towards bringing its own OS to the table

Perl already has far too many layers, one atop the other. Each added by a different person with a different agenda, and all intermingling in a way that is a nightmare to unravel. They never seem to throw anything away, just gloss over with a shiny new coat of code. Adding more layers isn't the right approach.

---

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"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

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