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diff --git a/src/code/thread.lisp b/src/code/thread.lisp
index 1f2ddcc..37e89ac 100644
--- a/src/code/thread.lisp
+++ b/src/code/thread.lisp
@@ -1,29 +1,75 @@
+;;;; support for threads needed at cross-compile time
+
+;;;; 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!THREAD")
 
-(sb!xc:defmacro with-recursive-lock ((mutex) &body body)
-  (declare (ignore #!-sb-thread mutex))
+(def!struct mutex
+  #!+sb-doc
+  "Mutex type."
+  (name nil :type (or null simple-string))
+  (value nil)
+  #!+(and sb-lutex sb-thread)
+  (lutex (make-lutex)))
+
+(def!struct spinlock
+  #!+sb-doc
+  "Spinlock type."
+  (name nil :type (or null simple-string))
+  (value 0))
+
+(sb!xc:defmacro with-mutex ((mutex &key (value '*current-thread*) (wait-p t))
+                            &body body)
+  #!+sb-doc
+  "Acquire MUTEX for the dynamic scope of BODY, setting it to
+NEW-VALUE or some suitable default value if NIL.  If WAIT-P is non-NIL
+and the mutex is in use, sleep until it is available"
+  #!-sb-thread (declare (ignore mutex value wait-p))
   #!+sb-thread
-  (with-unique-names (cfp)
-    `(let ((,cfp (sb!kernel:current-fp)))
-      (unless (and (mutex-value ,mutex)
-		   (sb!vm:control-stack-pointer-valid-p
-		    (sb!sys:int-sap
-		     (sb!kernel:get-lisp-obj-address (mutex-value ,mutex)))))
-	;; this punning with MAKE-LISP-OBJ depends for its safety on
-	;; the frame pointer being a lispobj-aligned integer.  While
-	;; it is, then MAKE-LISP-OBJ will always return a FIXNUM, so
-	;; we're safe to do that.  Should this ever change, this
-	;; MAKE-LISP-OBJ could return something that looks like a
-	;; pointer, but pointing into neverneverland, which will
-	;; confuse GC completely.  -- CSR, 2003-06-03
-	(get-mutex ,mutex (sb!kernel:make-lisp-obj (sb!sys:sap-int ,cfp))))
-      (unwind-protect
-	   (progn ,@body)
-	(when (sb!sys:sap= (sb!sys:int-sap
-			    (sb!kernel:get-lisp-obj-address
-			     (mutex-value ,mutex)))
-			   ,cfp)
-	  (release-mutex ,mutex)))))
+  (with-unique-names (got mutex1)
+    `(let ((,mutex1 ,mutex)
+           ,got)
+       (/show0 "WITH-MUTEX")
+       (unwind-protect
+            ;; FIXME: async unwind in SETQ form
+            (when (setq ,got (get-mutex ,mutex1 ,value ,wait-p))
+              (locally
+                  ,@body))
+         (when ,got
+           (release-mutex ,mutex1)))))
+  ;; KLUDGE: this separate expansion for (NOT SB-THREAD) is not
+  ;; strictly necessary; GET-MUTEX and RELEASE-MUTEX are implemented.
+  ;; However, there would be a (possibly slight) performance hit in
+  ;; using them.
   #!-sb-thread
-  `(progn ,@body))
+  `(locally ,@body))
 
+(sb!xc:defmacro with-recursive-lock ((mutex) &body body)
+  #!+sb-doc
+  "Acquires MUTEX for the dynamic scope of BODY. Within that scope
+further recursive lock attempts for the same mutex succeed. It is
+allowed to mix WITH-MUTEX and WITH-RECURSIVE-LOCK for the same mutex
+provided the default value is used for the mutex."
+  #!-sb-thread
+  (declare (ignore mutex))
+  #!+sb-thread
+  (with-unique-names (mutex1 inner-lock-p)
+    `(let* ((,mutex1 ,mutex)
+            (,inner-lock-p (eq (mutex-value ,mutex1) *current-thread*)))
+       (unwind-protect
+            (progn
+              (unless ,inner-lock-p
+                (get-mutex ,mutex1))
+              (locally
+                  ,@body))
+         (unless ,inner-lock-p
+           (release-mutex ,mutex1)))))
+  #!-sb-thread
+  `(locally ,@body))