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Re: [libmicrohttpd] Hang with MHD_OPTION_THREAD_POOL_SIZE on Windows

From: Jonathan McDougall
Subject: Re: [libmicrohttpd] Hang with MHD_OPTION_THREAD_POOL_SIZE on Windows
Date: Sun, 9 Dec 2018 13:47:11 -0500

On 12/9/18, Evgeny Grin <address@hidden> wrote:
> Why do you this that flag WSA_FLAG_OVERLAPPED should fix something?
> Looking at documentation, it should change nothing to non-overlapped I/O.

Most of my previous message was an attempt at explaining this, so I'll
have to repeat a few things.

Your link doesn't mention non-blocking sockets because it's specifically
about overlapped I/O. The article about overlapped vs. non-blocking

    Although the current Winsock implementation requires
    overlapped I/O attribute for nonblocking socket mode, [...]

It refers to another support article, #179942, but it's a 404. A google
search of its title finds a cached version, which says[2]:

    The Winsock 2 socket flag WSA_FLAG_OVERLAPPED needs to be
    set if the socket will be used in non-blocking mode when
    running on Windows NT 4.0. Failure to set this flag can
    result in subsequent Winsock API failure.

    [...] If the socket will be set to non-blocking mode (on
    Windows NT 4.0), the socket must also be created with its
    overlapped attribute set, even if no overlapped I/O will
    be performed with the socket.

Regarding the mentions of Windows NT 4.0, I don't see a date on the
article, but it talks about the differences between Windows 95 and NT
4.0, so I'd guess it was written in 1996-1997, at a time when the kernel
was different between these two versions. Since Windows has been using
the NT kernel since XP, I assume this article still applies to recent

These two articles, combined with other bits of information I found in
my other post, plus the fact that it does solve all the symptoms, leads
me to believe that the flag is mandatory for non-blocking sockets, even
if no overlapped I/O is performed.


Jonathan McDougall

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