[PATCH v3 2/2] Cygwin: signal: Do not handle signal when __SIGFLUSHFAST is sent

[Takashi Yano]

The commit a22a0ad7c4f0 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/256954.html
Addresses: https://cygwin.com/pipermail/cygwin/2024-December/256987.html
Fixes: d243e51ef1d3 ("Cygwin: signal: Fix deadlock between main thread and sig thread")
Fixes: a22a0ad7c4f0 ("Cygwin: signal: Do not handle signal when __SIGFLUSHFAST is sent")
Reported-by: Daisuke Fujimura <booleanlabel@gmail.com>
Reported-by: Jeremy Drake <cygwin@jdrake.com>
Reviewed-by:
Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>
---
 winsup/cygwin/sigproc.cc | 33 +++++++++++++++++++++++++++------
 1 file changed, 27 insertions(+), 6 deletions(-)

diff --git a/winsup/cygwin/sigproc.cc b/winsup/cygwin/sigproc.cc
index ba7818a68..4dcdd94de 100644
--- a/winsup/cygwin/sigproc.cc
+++ b/winsup/cygwin/sigproc.cc
@@ -751,8 +751,19 @@ 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)
-	_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;
     }
 
@@ -785,7 +796,20 @@ sig_send (_pinfo *p, siginfo_t& si, _cygtls *tls)
   if (wait_for_completion)
     {
       sigproc_printf ("Waiting for pack.wakeup %p", pack.wakeup);
-      rc = cygwait (pack.wakeup, WSSC);
+      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
@@ -806,9 +830,6 @@ sig_send (_pinfo *p, siginfo_t& si, _cygtls *tls)
       rc = -1;
     }
 
-  if (wait_for_completion && si.si_signo != __SIGFLUSHFAST)
-    _my_tls.call_signal_handler ();
-
 out:
   if (communing && rc)
     {
-- 
2.45.1