[lldb-dev] Pipe issue on LLDB Windows?

[Zachary Turner]

No worries.  Do you want to commit that fix by itself, or should I?


On Thu, Aug 7, 2014 at 2:30 PM, Deepak Panickal <deepak at codeplay.com> wrote:

> Yeah, I had done that, thanks.
> Just wanted to find out if it’s just us with the issue as didn’t see
> anything mentioned on the list.
>
> On 7 Aug 2014, at 22:26, Zachary Turner <zturner at google.com> wrote:
>
> 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
>>>>>
>>>>
>>>>
>>>
>>>
>>
>>
>
>
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