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

[Zebediah Figura]

On 3/5/22 02:24, Jinoh Kang wrote:
> 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?  ;-)

Not at all ;-)

> 
>>
>> 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.
> 
> 
Right. Maybe we could make use of async_set_completion_callback() 
instead? I think the only reason that can't work is if the sock name 
needs to be updated and visible *before* the I/O is necessarily complete.