scp stalls on uploading in cygwin 3.5 current master.

Fri Aug 25 08:48:32 GMT 2023

On 2023年8月24日 10:59:33 +0200
Corinna Vinschen wrote:
> > I'm not sure why at all, however, the following patch seems to
> > solve the issue.
> > 
> > diff --git a/winsup/cygwin/select.cc b/winsup/cygwin/select.cc
> > index 7b9473849..de5794c9f 100644
> > --- a/winsup/cygwin/select.cc
> > +++ b/winsup/cygwin/select.cc
> > @@ -1790,7 +1790,7 @@ peek_socket (select_record *me, bool)
> > if (events & FD_WRITE)
> > 	{
> > 	 wfd_set w = { 1, { fh->get_socket () } };
> > -	 TIMEVAL t = { 0 };
> > +	 TIMEVAL t = { .tv_sec = 0, .tv_usec = 1 };
> > 
> > 	 if (_win32_select (0, NULL, &w, NULL, &t) == 0)
> > 	 events &= ~FD_WRITE;
>> Yeah, this is weird. A TIMEVAL value of 0 indicates non-blocking,
> so why should waiting a usec make that better? It also potentially
> slows down Cygwin's select noticably if multiple sockets are part
> of the descriptor set.
>> Hmmm.
>> Is it possible that _win32_select returns with SOCKET_ERROR for 
> some reason?
>> Unfortunately I'm a bit swamped ATM, but rather than setting t to 1
> usec, what if the check goes:
>> if (_win32_select (0, NULL, &w, NULL, &t) != 1)
>> ?

This did not help. I looked into this deeper and noticed that:
1) _win32_select() sometimes returns 0.
2) If _win32_select() returns 0, WaitForMultipleObjects(..., INFINITE)
 is called in thread_socket().
3) WaitForMultipleObjects() sometimes does not return for FD_WRITE
 for unknown reason.
This causes the stall.
-- 
Takashi Yano <takashi.yano@nifty.ne.jp>