[newlib-cygwin/main] Cygwin: don't wait infinitely on a pthread cancel event

[newlib-cygwin/main] Cygwin: don't wait infinitely on a pthread cancel event

[Corinna Vinschen]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=a02144808c5bc4e9753bfeabf06313c6413e1cd3

commit a02144808c5bc4e9753bfeabf06313c6413e1cd3
Author:     Corinna Vinschen <corinna@vinschen.de>
AuthorDate: Mon Jul 17 18:02:04 2023 +0200
Commit:     Corinna Vinschen <corinna@vinschen.de>
CommitDate: Tue Jul 18 22:21:36 2023 +0200

    Cygwin: don't wait infinitely on a pthread cancel event
    
    Starting with commit 42faed412857 ("* thread.h (class pthread): Add bool
    member canceled."), pthread::testcancel waits infinitely on cancel_event
    after it checked if the canceled variable is set.  However, this might
    introduce a deadlock, if the thread calling pthread_cancel is terminated
    after setting canceled to true, but before calling SetEvent on cancel_event.
    
    In fact, it's not at all necessary to wait infinitely.  By definition,
    the thread is only canceled if cancel_event is set.  The canceled
    variable is just a helper to speed up code.  We can safely assume that
    the thread hasn't been canceled yet, if canceled is set, but cancel_event
    isn't.
    
    Fixes: 42faed412857 ("* thread.h (class pthread): Add bool member canceled.")
    Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

Diff:
---
 winsup/cygwin/thread.cc | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/winsup/cygwin/thread.cc b/winsup/cygwin/thread.cc
index afddf42821ad..7bb4f9fc8341 100644
--- a/winsup/cygwin/thread.cc
+++ b/winsup/cygwin/thread.cc
@@ -962,12 +962,9 @@ pthread::testcancel ()
      pthread_testcancel function a lot without adding the overhead of
      an OS call.  Only if the thread is marked as canceled, we wait for
      cancel_event being really set, on the off-chance that pthread_cancel
-     gets interrupted before calling SetEvent. */
-  if (canceled)
-    {
-      WaitForSingleObject (cancel_event, INFINITE);
-      cancel_self ();
-    }
+     gets interrupted or terminated before calling SetEvent. */
+  if (canceled && IsEventSignalled (cancel_event))
+    cancel_self ();
 }
 
 /* Return cancel event handle if it exists *and* cancel is not disabled.