[lldb-dev] Pipe issue on LLDB Windows?

[Zachary Turner]

Ahh, I see.  Can you just put an #ifdef _WIN32 that doesn't add the pipe_fd
to the fd_set for Windows?  It's broken either way, but at least this way
it's less broken.


On Thu, Aug 7, 2014 at 2:25 PM, Deepak Panickal <deepak at codeplay.com> wrote:

> Yes, we have a regression in behaviour.
>
> Before _pipe() was added, pipes were ignored on Windows. They were
> not added to the read_fds list for select(). So, the BytesAvailable() did
> not error.
>
> However, now since pipes are created, it is added to the read_fds list and
> then select() fails like you said, because it is not a socket. It fails
> with a WSAENOTSOCK error. Due to this, the BytesAvailable() errors out and
> no data is read from the remote socket connection.
>
> I only found this after the merge, as we were not able to read data from
> our remote debug stub.
>
> On 7 Aug 2014, at 22:15, Zachary Turner <zturner at google.com> wrote:
>
> Yes, that's correct.  It's just that on Windows, select() won't accept a
> pipe, it will just return an error.  Which we also don't handle correctly,
> it turns out, since we assume that the error it's returning is an errno,
> which on Windows it's not.
>
> That said, I'm pretty sure ConnectionFileDescriptor has never worked on
> Windows.  Are you seeing a regression in behavior?  i.e. something worked
> before you merged, but now it doesn't?
>
>
> On Thu, Aug 7, 2014 at 2:06 PM, Deepak Panickal <deepak at codeplay.com>
> wrote:
>
>> Ah, so it is a known issue. Thanks, got it now.
>> We recently did a merge which brought in the new changes from upstream.
>>
>> Isn’t the ::select used in ConnectionFileDescriptor to wait till input is
>> available?
>> Not just from the command pipe, but also from the sockets.
>>
>> On 7 Aug 2014, at 21:38, Zachary Turner <zturner at google.com> wrote:
>>
>> Sorry, hit enter too soon.  I have been thinking about next steps for
>> fixing this in the longer term.  I think the way to go is that on Windows,
>> ConnectionFileDescriptor shouldn't even use select at all, nor should it
>> use the command pipe.  The purpose of the command pipe seems to be so that
>> various interrupt commands can be sent to interrupt the select, and then
>> terminate the connection or something else so that it doesn't block forever.
>>
>> On Windows, the closest equivalent to select is WaitForMultipleObjects.
>>  So I think on Windows we need to switch to using WFMO instead of select().
>>  The command pipe will be replaced by various event objects, which the user
>> will set according to which interruption command they want to send.  WFMO
>> doesn't accept sockets though, so we need to call WSAEventSelect() to get
>> an event handle corresponding to read/write operations on the socket.
>>
>> There's numerous other portability issues with this class currently, most
>> notably that select() on windows doesn't set errno
>>
>>
>> On Thu, Aug 7, 2014 at 1:34 PM, Zachary Turner <zturner at google.com>
>> wrote:
>>
>>> This is a known issue.  But I don't think this is a regression.  It's
>>> just always been this way.  Basically on Windows, select() only deals with
>>> sockets.  It doesn't work with pipes, files, or anything else.  In other
>>> words, ConnectionFileDescriptor is just fundamentally broken on Windows.  I
>>> recently pushed a large refactor to the socket logic in
>>> ConnectionFileDescriptor which is aimed at addressing this.  But it's only
>>> one step of what I think will be a long process to get
>>> ConnectionFileDescriptor working on Windows.
>>>
>>>
>>> On Thu, Aug 7, 2014 at 1:01 PM, Deepak Panickal <deepak at codeplay.com>
>>> wrote:
>>>
>>>> Hi,
>>>>
>>>> I have been seeing an issue with the refactored pipe support changes on
>>>> Windows using _pipe().
>>>>
>>>> This is specifically at the ::select function in
>>>> ConnectionFileDescriptor::BytesAvailable().
>>>> On Windows, the ::select fails if the pipe file descriptor is also
>>>> included and so the connection fails.
>>>>
>>>>
>>>> http://llvm.org/viewvc/llvm-project/lldb/trunk/source/Core/ConnectionFileDescriptor.cpp?view=markup
>>>>
>>>> Wanted to ask if anybody else on Windows is seeing any such issue?
>>>>
>>>> Thanks,
>>>> Deepak
>>>>
>>>>
>>>> _______________________________________________
>>>> lldb-dev mailing list
>>>> lldb-dev at cs.uiuc.edu
>>>> http://lists.cs.uiuc.edu/mailman/listinfo/lldb-dev
>>>>
>>>
>>>
>>
>>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/lldb-dev/attachments/20140807/0c6eadf2/attachment.html>