Add Thread.ignore_deadlock accessor

Setting this to true disables the deadlock detector.  It should
only be used in cases where the deadlock could be broken via some
external means, such as via a signal.

Now that $SAFE is no longer used, replace the safe_level_ VM flag
with ignore_deadlock for storing the setting.

Fixes [Bug #13768]

1 files changed, 3 insertions, 0 deletions

diff --git a/NEWS.md b/NEWS.md
index 83b7a5af9a..c7a4036a0a 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -178,6 +178,9 @@ Outstanding ones only.
       blocking. [[Feature #16786]]
     * `Thread#join` invokes the scheduler hooks `block`/`unblock` in a
       non-blocking execution context. [[Feature #16786]]
+    * `Thread.ignore_deadlock` accessor for disabling the default deadlock
+      detection, allowing the use of signal handlers to break deadlock.
+      [[Bug #13768]]
 
 * Mutex