Re: IOCPs again

From:

"Igor Tandetnik" <itandetnik@mvps.org>

Newsgroups:

microsoft.public.vc.language,microsoft.public.vc.mfc

Date:

Mon, 20 Aug 2007 08:08:21 -0400

Message-ID:

<eV6GPLy4HHA.1484@TK2MSFTNGP06.phx.gbl>

"SD" <sd@nospamgroup.com> wrote in message
news:1B4D7535-E787-4C7F-88FC-A5714073BF69@microsoft.com

1. What is the purpose of the OVERLAPPED structure in an IOCP? It is
not very clear from MSDN. Do we need 1 such structure for every
read/write operation?

Yes. Basically, OVERLAPPED pointer uniquely identifies a particular
asynchronous I/O operation. You pass it to, say, ReadFile, and get it
back in GetQueuedCompletionStatus.

It is common to maintain additional per-operation state by extending
OVERLAPPED structure with your own fields - like this:

struct OpState {
    OVERLAPPED overlapped;
    int moreState;
};

// or

struct OpState : public OVERLAPPED {
    int moreState;
};

2. Also, MSDN says that once a handle(like socket) is associated with
an IOCP, it cannnot be used to do ReadFile/ WriteFile operations. In
that case how do you send/ receive data?

Where do you see that? You must have misunderstood something.
--
With best wishes,
Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925