[PATCH v4 4/8] server: Defer postprocessing until after setting initial status in send_socket handler.

[Jinoh Kang]

On 3/5/22 09:13, Zebediah Figura wrote:
> On 3/4/22 13:16, Jinoh Kang wrote:
>> On 3/5/22 02:51, Zebediah Figura wrote:
>>> On 3/3/22 07:30, Jinoh Kang wrote:
>>>> This allows the client to postpone the initial I/O until the server has
>>>> queued the I/O request.  The server should perform the postprocessing
>>>> only after the initial I/O has been done.
>>>>
>>>> In the case of send_socket, the manipulation of event flags shall
>>>> ideally be done *after* (not *before*) the client has attempted the
>>>> initial I/O, since the outbound queue status of the socket may change in
>>>> the meanwhile.  Also, the implicitly bound address is available only
>>>> after the send* system call has been performed.
>>>>
>>>> Signed-off-by: Jinoh Kang <jinoh.kang.kr at gmail.com>
>>>> ---
>>>>
>>>> Notes:
>>>>       v1 -> v2:
>>>>       - pass around total size of data to be transmitted
>>>>       - detect short write in send_socket_initial_callback
>>>>       v2 -> v3: no changes
>>>>       v3 -> v4: no changes
>>>>
>>>>    dlls/ntdll/unix/socket.c | 15 ++++++++++++++
>>>>    server/protocol.def      |  1 +
>>>>    server/sock.c            | 42 +++++++++++++++++++++++++++-------------
>>>>    3 files changed, 45 insertions(+), 13 deletions(-)
>>>>
>>>
>>> I still am failing to see the need to do this, especially by adding a new callback. What's preventing send_socket from working the same way as recv_socket?
>>
>> As stated in the commit message, none of the actions in send_socket_initial_callback can be performed *before* the initial I/O.
>>
>> In send_socket, "send() calls only clear and reselect events if unsuccessful."
>> We can tell if the I/O has succeeded only after set_async_direct_result.
>> Therefore, we can only clear and reselect events after the client tells us the initial I/O has been unsuccessful.
>>
> Right, sorry, I'm not thinking this through, or reading apparently...

No need to be sorry; I'm sometimes guilty of this too :-/.  I'll try to be more clear the next time.

> 
> I still am not thrilled about adding a new callback, though, at least if it can be avoided.

To be fair, extending structs and introducing indirect calls are a pet peeve of mine too.

> In this case I wonder if we can make use of sock_reselect_async().
> 
> The exact conditions (and timing) under which we need to clear the AFD_POLL_WRITE bit are not really clear. In particular the correct condition may not be "status != STATUS_SUCCESS" but "status == STATUS_PENDING || status == STATUS_DEVICE_NOT_READY". I can't off the top of my head think of any interesting cases where send() returns an error (other than EWOULDBLOCK) but subsequent calls can succeed...

Does STATUS_NO_MEMORY count?  ;-)

> 
> But assuming that we only really need to clear flags when the kernel send buffer is full, I think the right thing to do would be to clear events if "async_waiting( &sock->write_q )".

We still need to account for nonblocking I/O (STATUS_DEVICE_NOT_READY), and also is_short_write, which is another indicator for a full send buffer.  Otherwise, it breaks ws2_32:sock:test_write_events.
Also, note the implicitly bound address.

In any case I think the co-routine pattern is inevitable due to the client-server role split.  In this case, AFD.SYS can do both pre- and post-processing inside a single function, but wineserver can't block for the client to finish the I/O.


-- 
Sincerely,
Jinoh Kang