+(defun mutex-value (mutex)
+ "Current owner of the mutex, NIL if the mutex is free. May return a
+stale value, use MUTEX-OWNER instead."
+ (mutex-%owner mutex))
+
+(defun holding-mutex-p (mutex)
+ "Test whether the current thread is holding MUTEX."
+ ;; This is about the only use for which a stale value of owner is
+ ;; sufficient.
+ (eq sb!thread:*current-thread* (mutex-%owner mutex)))
+
+(defsetf mutex-value set-mutex-value)
+
+(declaim (inline set-mutex-value))
+(defun set-mutex-value (mutex value)
+ (declare (ignore mutex value))
+ (error "~S is no longer supported." '(setf mutex-value)))
+
+(define-compiler-macro set-mutex-value (&whole form mutex value)
+ (declare (ignore mutex value))
+ (warn "~S is no longer supported, and will signal an error at runtime."
+ '(setf mutex-value))
+ form)
+