Async Watcher Issue on Windows

Marc Lehmann schmorp at
Sun Feb 19 02:36:20 CET 2012

On Thu, Feb 16, 2012 at 06:07:13PM +0200, Anton Kirilov <akirilov at> wrote:
> I have stumbled upon an issue with async watchers on Windows that has been previously reported on the mail list - ev_async_send() fails (silently) to signal the watcher. My OS is Windows XP SP3, and I have a fully updated version of Visual C++ Express 2010.

maybe this is an xp thing, I will think about it.

> Finally, WriteFile() fails because it has specific expectations for its parameters that are not satisfied, as documented here:

Well, the documentation is contradicting - WriteFile says the lpOverlapped
parameter can be NULL, unless the overlapped flag is specified when
opening the hFile, which is not the case (the socekt call does not specify
that flag), so this is a windows bug somewhere - which explains why
apparently only some platforms are affected (i.e. not the ones I try it
on, windows 2000 and win7).

I'll have a look whether WSASocket works, thanks for verifying it on your

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