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Date: Thu, 24 Aug 2023 12:31:31 +0900
To: cygwin AT cygwin DOT com
Subject: Re: scp stalls on uploading in cygwin 3.5 current master.
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From: Takashi Yano via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>
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On Thu, 24 Aug 2023 06:05:02 +0900
Takashi Yano wrote:
> Hi Corinna,
> 
> After the commit dedbbd74d0a8, "scp file server:." stalls.
> I confirmed this when the "server" is a Linux machine.
> The problem does not occur if it is reverted.
> 
> Could you please have a look?
> 
> commit dedbbd74d0a8f3b7dfae6188321703a47bb8a2b3
> Author: Corinna Vinschen <corinna AT vinschen DOT de>
> Date:   Tue Aug 1 14:22:55 2023 +0200
> 
>     Cygwin: select: workaround FD_WRITE network event handling
>     
>     The FD_WRITE event is a false friend.  It indicates ready to write
>     even if the next send fails with WSAEWOULDBLOCK.  *After* the fact,
>     FD_WRITE will be cleared until sending is again possible, but that
>     is too late for a select/write loop.
>     
>     Workaround that by using the WinSock select function when peeking
>     at a socket and FD_WRITE gets indicated. WinSock select fortunately
>     indicates writability correctly.
>     
>     Fixes: 70e476d27be8 ("(peek_socket): Use event handling for peeking socket.")
>     Signed-off-by: Corinna Vinschen <corinna AT vinschen DOT de>

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;

-- 
Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>

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