Cygwin: signal: Do not handle signal when __SIGFLUSHFAST is sent

The commit a22a0ad was not exactly the correct thing. Even with
the patch, some hangs still happen. This patch overrides the previous
commit to fix these hangs.

Addresses: https://cygwin.com/pipermail/cygwin/2024-December/256987.html
Fixes: a22a0ad ("Cygwin: signal: Do not handle signal when __SIGFLUSHFAST is sent")
Reported-by: Jeremy Drake <[email protected]>
Reviewed-by:
Signed-off-by: Takashi Yano <[email protected]>

Author: tyan0

winsup/cygwin/sigproc.cc

@@ -751,14 +751,21 @@ sig_send (_pinfo *p, siginfo_t& si, _cygtls *tls)
       res = WriteFile (sendsig, leader, packsize, &nb, NULL);
       if (!res || packsize == nb)
 	break;
-      if (cygwait (NULL, 10, cw_sig_eintr) == WAIT_SIGNALED
-	  && pack.si.si_signo != __SIGFLUSHFAST)
-	_my_tls.call_signal_handler ();
+      if (pack.si.si_signo == __SIGFLUSHFAST)
+	Sleep (10);
+      else /* Handle signals */
+	do
+	  {
+	    DWORD rc = WaitForSingleObject (_my_tls.get_signal_arrived (), 10);
+	    if (rc == WAIT_OBJECT_0)
+	      {
+		_my_tls.call_signal_handler ();
+		continue;
+	      }
+	  }
+	while (false);
       res = 0;
     }
-  /* Re-assert signal_arrived which has been cleared in cygwait(). */
-  if (_my_tls.sig)
-    _my_tls.set_signal_arrived ();
 
   if (!res)
     {
@@ -789,16 +796,20 @@ sig_send (_pinfo *p, siginfo_t& si, _cygtls *tls)
   if (wait_for_completion)
     {
       sigproc_printf ("Waiting for pack.wakeup %p", pack.wakeup);
-      do
-	{
-	  rc = cygwait (pack.wakeup, WSSC, cw_sig_eintr);
-	  if (rc == WAIT_SIGNALED && pack.si.si_signo != __SIGFLUSHFAST)
-	    _my_tls.call_signal_handler ();
-	}
-      while (rc != WAIT_OBJECT_0 && rc != WAIT_TIMEOUT);
-      /* Re-assert signal_arrived which has been cleared in cygwait(). */
-      if (_my_tls.sig)
-	_my_tls.set_signal_arrived ();
+      if (pack.si.si_signo == __SIGFLUSHFAST)
+	rc = WaitForSingleObject (pack.wakeup, WSSC);
+      else /* Handle signals */
+	do
+	  {
+	    HANDLE w[2] = {pack.wakeup, _my_tls.get_signal_arrived ()};
+	    rc = WaitForMultipleObjects (2, w, FALSE, WSSC);
+	    if (rc == WAIT_OBJECT_0 + 1) /* signal arrived */
+	      {
+		_my_tls.call_signal_handler ();
+		continue;
+	      }
+	  }
+	while (false);
       ForceCloseHandle (pack.wakeup);
     }
   else