Only set locking thread if no interrupts

If the lock is acquired but we are immediately interrupted by
another thread, it will be unlocked while leaving the lockingThread
field set. This will cause all future locks by other fibers on that
thread to trigger a deadlock error, since the lock will appear to
have been acquired by a different fiber on that thread.

Patch by @yamam.

Fixes jruby#9218

Author: headius

core/src/main/java/org/jruby/ext/thread/Mutex.java

@@ -124,8 +124,6 @@ public IRubyObject lock(ThreadContext context) {
             }
         }
 
-        this.lockingThread = parentThread;
-
         // always check for thread interrupts after acquiring lock
         try {
             thread.pollThreadEvents(context);
@@ -137,6 +135,9 @@ public IRubyObject lock(ThreadContext context) {
             Helpers.throwException(t);
         }
 
+        // set locking thread once successfully locked with no interrupts
+        this.lockingThread = parentThread;
+
         return this;
     }