[Box Backup-commit] Re: #3: Merge Win32 branch

[Chris Wilson]

Hi Charles,

On Sun, 25 Mar 2007, trac at fluffy.co.uk wrote:

> [1486] I don't know if I can do this, but I'm going to try :-)
>
> I'd like to veto this change. You seem to have done a partial re- 
> implementation of a completion port - see CreateIoCompletionPort and 
> friends.

Thanks for the suggestion, but I'm afraid that after reading the 
CreateIoCompletionPort docs I'm still not completely sure how I could use 
it to replace [1486].

So far, what I understand (I think) is that the command socket thread, 
instead of calling WaitForMultipleObjects, would call 
GetQueuedCompletionStatus, which blocks until either (i) the main thread 
posts a message to the port with PostQueuedCompletionStatus, or (ii) a 
packet is received over the command socket by the pending overlapped I/O. 
Is that correct?

What bothers me is that MSDN says "After an instance of an open file is 
associated with an I/O completion port, it cannot be used in the 
ReadFileEx or WriteFileEx function."

I assume that this means that I have to use overlapped I/O for both 
reading and writing from the pipe? I don't care about completion of 
writes, although I suppose I could dispatch the next waiting message (if 
any) to the pipe in this case.

And how do I actually read or write on the pipe, if ReadFileEx and 
WriteFileEx are forbidden? Do good old ReadFile and WriteFile work 
properly?

I have a feeling that implementing this will move the WinNamedPipeStream 
API so far away from POSIX that I will have to create a new class that 
doesn't extend IOStream for this purpose. While it might be a cleaner 
solution to the current overlapped/nonoverlapped read branches in the 
code, I'm worried about the duplication of code and possible maintenance 
headaches.

Are there any samples of using CreateIoCompletionPort and 
PostQueuedCompletionStatus that I can freely copy and adapt for use in 
this case?


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