[newlib-cygwin] Cygwin: signal: Increase chance of handling signal in main thread

[Takashi Yano]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=c48d58d838d90df6247123c487686699742d75de

commit c48d58d838d90df6247123c487686699742d75de
Author: Takashi Yano <takashi.yano@nifty.ne.jp>
Date:   Tue Dec 3 22:14:44 2024 +0900

    Cygwin: signal: Increase chance of handling signal in main thread
    
    If the process() fails and the signal remains in the queue, the most
    possible reason is that the target thread is already armed by another
    signal and does not handle it yet. With this patch, to increase the
    chance of handling it in the other threads, call yield() before
    retrying process().
    
    Addresses: https://cygwin.com/pipermail/cygwin/2024-November/256744.html
    Fixes: e10f822a2b39 ("Cygwin: signal: Handle queued signal without explicit __SIGFLUSH")
    Reported-by: Christian Franke <Christian.Franke@t-online.de>
    Reviewed-by:
    Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>

Diff:
---
 winsup/cygwin/sigproc.cc | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/winsup/cygwin/sigproc.cc b/winsup/cygwin/sigproc.cc
index c74596f31..9680f6968 100644
--- a/winsup/cygwin/sigproc.cc
+++ b/winsup/cygwin/sigproc.cc
@@ -1325,7 +1325,10 @@ wait_sig (VOID *)
 	pack.si.si_signo = __SIGFLUSH;
       else if (sigq.start.next
 	       && PeekNamedPipe (my_readsig, NULL, 0, NULL, &nb, NULL) && !nb)
-	pack.si.si_signo = __SIGFLUSH;
+	{
+	  yield ();
+	  pack.si.si_signo = __SIGFLUSH;
+	}
       else if (!ReadFile (my_readsig, &pack, sizeof (pack), &nb, NULL))
 	Sleep (INFINITE);	/* Assume were exiting.  Never exit this thread */
       else if (nb != sizeof (pack) || !pack.si.si_signo)