;;;; finalization based on weak pointers ;;;; This software is part of the SBCL system. See the README file for ;;;; more information. ;;;; ;;;; This software is derived from the CMU CL system, which was ;;;; written at Carnegie Mellon University and released into the ;;;; public domain. The software is in the public domain and is ;;;; provided with absolutely no warranty. See the COPYING and CREDITS ;;;; files for more information. (in-package "SB!IMPL") (defglobal **finalizer-store** nil) (defglobal **finalizer-store-lock** (sb!thread:make-mutex :name "Finalizer store lock.")) (defmacro with-finalizer-store-lock (&body body) `(sb!thread::with-system-mutex (**finalizer-store-lock** :without-gcing t) ,@body)) (defun finalize (object function &key dont-save) #!+sb-doc "Arrange for the designated FUNCTION to be called when there are no more references to OBJECT, including references in FUNCTION itself. If DONT-SAVE is true, the finalizer will be cancelled when SAVE-LISP-AND-DIE is called: this is useful for finalizers deallocating system memory, which might otherwise be called with addresses from the old image. In a multithreaded environment FUNCTION may be called in any thread. In both single and multithreaded environments FUNCTION may be called in any dynamic scope: consequences are unspecified if FUNCTION is not fully re-entrant. Errors from FUNCTION are handled and cause a WARNING to be signalled in whichever thread the FUNCTION was called in. Examples: ;;; GOOD, assuming RELEASE-HANDLE is re-entrant. (let* ((handle (get-handle)) (object (make-object handle))) (finalize object (lambda () (release-handle handle))) object) ;;; BAD, finalizer refers to object being finalized, causing ;;; it to be retained indefinitely! (let* ((handle (get-handle)) (object (make-object handle))) (finalize object (lambda () (release-handle (object-handle object))))) ;;; BAD, not re-entrant! (defvar *rec* nil) (defun oops () (when *rec* (error \"recursive OOPS\")) (let ((*rec* t)) (gc))) ; or just cons enough to cause one (progn (finalize \"oops\" #'oops) (oops)) ; GC causes re-entry to #'oops due to the finalizer ; -> ERROR, caught, WARNING signalled" (unless object (error "Cannot finalize NIL.")) (with-finalizer-store-lock (push (list (make-weak-pointer object) function dont-save) **finalizer-store**)) object) (defun deinit-finalizers () ;; remove :dont-save finalizers (with-finalizer-store-lock (setf **finalizer-store** (delete-if #'third **finalizer-store**))) nil) (defun cancel-finalization (object) #!+sb-doc "Cancel any finalization for OBJECT." ;; Check for NIL to avoid deleting finalizers that are waiting to be ;; run. (when object (with-finalizer-store-lock (setf **finalizer-store** (delete object **finalizer-store** :key (lambda (list) (weak-pointer-value (car list)))))) object)) (defun run-pending-finalizers () (let (pending) (with-finalizer-store-lock (setf **finalizer-store** (delete-if (lambda (list) (when (null (weak-pointer-value (car list))) (push (second list) pending) t)) **finalizer-store**))) ;; We want to run the finalizer bodies outside the lock in case ;; finalization of X causes finalization to be added for Y. (dolist (fun pending) (handler-case (funcall fun) (error (c) (warn "Error calling finalizer ~S:~% ~S" fun c))))) nil)