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Re: unix domain socket with shared memory ?

----- Original Message -----
From: "Ralf Habacker" <>
To: "cygwin" <>
Sent: Thursday, February 07, 2002 1:17 AM
Subject: unix domain socket with shared memory ?

> Hi all,
> cfg has told me about the current process of cygwin daemon
implementation with ipc support.
> I initial have heard last year, that this work would be started, but
because of so much other work I have lost the
> contact to the ongoing process.

It's currently paused, waiting for the development team to persuade
Chris that the _core_ (not the IPC part) is ready for (finaly filenaming
and then) inclusion.

> Now I was looking into the ongoing work and it seems to me in a mostly
read state, isn't it. I like to say: Great
> work to all who have worked on it. :-)

Thank you. The main folk are Egor Duda who created an inital
proof-of-concept for solving a security issue, most of the developers
list bouncing round ideas, and then I (*bow*) took Egors proof of
concept and created the generic daemon, and the win9x support that it
now has. Gary R. Van Sickle has also spent some time recently being a
guinea pig, which I appreciate :].

> The reason why I'm writing this is that I have recognized some
performance issues with unix domain sockets, which

> Because the cygwin-daemon branch provides the long missed ipc support,
the way for for speeding up unix domain
> sockets with a shared memory implementation may be free. (I not be not
first one, who tells about this, because I
> have seen some guys before talking about this possibility)

Hmm, the cygwin-daemon IPC implementation may allow this, but so does
the existing mmap implementation. So I think a better approach may be
via mmap (more mature code) with the daemon providing
cross-process-persistence (if needed).

> One open topic for me is how to handle forking. I imagine, that
because the file handles are duplicated, the shared
> memory has to be duplicatd too, but because the socket file name is
the same, does it use the same shared memory
> area as the parent or not ???

Forking is easy to implement (see the fixup_after_fork functions) but
shouldn't be needed if implemented on top of mmap or IPC memory regions.
What maybe an issue is the logic for how it should behave.

If you write, who reads? The parent or the child? The first reader? Once
this question is answered, you will find making fork() work straight
forward. Advice can be offered at that point if needed.

> My intention whis this thread is to make sure, that this strategy is a
possible way and I'm willing to spent some t
> ime to get this running, although I think I'm not be able to handle
this whole task alone.

Yes, it's possible. Is the daemon needed? Maybe not, maybe. You will get
assistance in doing this.


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