added register-finalizer-and-custodian-shutdown

pkgs/racket-doc/scribblings/foreign/custodian.scrbl

@@ -38,7 +38,8 @@ if the finalizer is not run in atomic mode, then there's no guarantee
 that either of the custodian or finalizer callbacks has completed by
 the time that the custodian shutdown has completed; @racket[v] might
 be no longer registered to the custodian, while the finalizer for
-@racket[v] might be still running or merely queued to run.}
+@racket[v] might be still running or merely queued to run. See also
+@racket[register-finalizer-and-custodian-shutdown].}
 
 
 @defproc[(unregister-custodian-shutdown [v any/c]
@@ -48,3 +49,18 @@ be no longer registered to the custodian, while the finalizer for
 Cancels a custodian-shutdown registration, where @racket[registration]
 is a previous result from @racket[register-custodian-shutdown] applied
 to @racket[v].}
+
+@defproc[(register-finalizer-and-custodian-shutdown
+                 [v any/c]
+                 [callback (any/c . -> . any)]
+                 [custodian custodian? (current-custodian)]
+                 [#:at-exit? at-exit? any/c #f]
+                 [#:weak? weak? any/c #f])
+         void?]{
+
+Registers @racket[callback] to be applied (in atomic mode) to
+@racket[v] when @racket[custodian] is shutdown or when @racket[v] is
+about to be collected by the garbage collector, whichever happens
+first. The @racket[callback] is only applied to @racket[v] once.
+
+@history[#:added "6.1.1.6"]}

racket/collects/ffi/unsafe/custodian.rkt

@@ -1,7 +1,9 @@
 #lang racket/base
-(require ffi/unsafe)
+(require ffi/unsafe
+         ffi/unsafe/atomic)
 
 (provide (protect-out register-custodian-shutdown
+                      register-finalizer-and-custodian-shutdown
                       unregister-custodian-shutdown))
 
 (define _Scheme_Custodian_Reference-pointer
@@ -41,3 +43,20 @@
 
 (define (unregister-custodian-shutdown obj mref)
   (scheme_remove_managed mref obj))
+
+(define (register-finalizer-and-custodian-shutdown value callback
+                                                   [custodian (current-custodian)]
+                                                   #:at-exit? [at-exit? #f])
+  (define done? #f)
+  (define (do-callback obj) ; called in atomic mode
+    (unless done?
+      (set! done? #t)
+      (callback obj)))
+  (define registration
+    (register-custodian-shutdown value do-callback custodian #:at-exit? at-exit?))
+  (register-finalizer value
+    (lambda (obj)
+      (call-as-atomic
+       (lambda ()
+         (unregister-custodian-shutdown obj registration)
+         (do-callback obj))))))