[Libevent-users] Re: IOCP writes

[Toby Douglass]

Rhythmic Fistman wrote:
>> From: "Toby Douglass" <toby.douglass at summerblue.net>

>> I've realised, though, that if you issue a write on a socket which
>> currently has an outstanding reading, when the IOCP completes, you don't
>> immediately know which operation has completed.
> 
> You use two different OVERLAPPED structures. The pointers returned
> by GetQueuedCompletionStatus will be different.

Yup.  I'll be passing in a struct which contains that overlapped as its
first member.  When it comes back to be, I'll cast the overlapped
pointer to my struct type.  I think this means though I need a malloc
per write, since I have to create the overlapped structure.  That's bad,
since the point of this is high throughput.

>> The obvious answer is to use select() to check the socket when an IOCP
>> completes, but that's very awkward, because of the race conditions, for
>> the other operation could complete in the time between the IOCP complete
>> and select() and you have multiple threads calling GQCS concurrently.
>> Locking would be required, which would be Bad.
> 
> That's doesn't sound right..., IOCP type progs really shouldn't need 
> select.

Quite right.