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Date:	Tue, 24 Feb 2026 10:36:28 +0900
To:	cygwin AT cygwin DOT com
Subject:	General clipboard issue on cygwin (mintty, putclip, getclip,
	/dev/clipboard)
Message-Id:	<20260224103628.fdbd7396311092795834c24f@nifty.ne.jp>
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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>
Cc:	Mark Geisert <mark AT maxrnd DOT com>
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Hi,

I encountered a clipboard issue common to cygwin.

Affected components:
/dev/clipboard, putclip/getclip, mintty

The issue:
If the clipbard is opened by `OpenClipboard(NULL)`, occasionally
SetClipboardData() and GetClipboardData() fails with
ERROR_CLIPBOARD_NOT_OPEN.

When UltraVNC Viewer (https://uvnc.com/) is opened, this issue
happens with a very high probability (> ~90%).

$ echo AAAA > /dev/clipboard
echo: write error: Permission denied

On mintty, text selection by mouse and clicking center button
fails at the first attempt.

For putlclip/getclip, the following command outputs nothing
in a few attempts. ("ABCD" is lost.)
$ echo ABCD |putclip; for a in `seq 100`; do getclip |putclip; done; getclip

$


Solutions:
This can be solved by passing non-zero HWND to OpenClipboard().
Therefore, as for mintty, the following patch is ok I think.
diff --git a/src/winclip.c b/src/winclip.c
index 12c54525..a7cbe365 100644
--- a/src/winclip.c
+++ b/src/winclip.c
@@ -1324,7 +1324,7 @@ static void
 do_win_paste(bool do_path)
 {
   //printf("OpenClipboard win_paste\n");
-  if (!OpenClipboard(null))
+  if (!OpenClipboard(wnd))
     return;

   if (cfg.input_clears_selection)

However, for /dev/clipbard and {put|get}clip, there is no
suitable HWND to pass to OpenClipboard(). Fortunately, I
found the patch attached solves the /dev/clipboard issue.

This is not smart, however it works.

I think similar patch is ok for putclip/getclip.

Any suggestions and comments will be appreciated.

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

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