-;;; This lock is seized in the compiler, and related areas: the
-;;; compiler is not presently thread-safe
-(defvar *big-compiler-lock*
- (sb!thread:make-mutex :name "big compiler lock"))
+(defvar *stack-allocate-dynamic-extent* t
+ "If true (the default), the compiler respects DYNAMIC-EXTENT declarations
+and stack allocates otherwise inaccessible parts of the object whenever
+possible. Potentially long (over one page in size) vectors are, however, not
+stack allocated except in zero SAFETY code, as such a vector could overflow
+the stack without triggering overflow protection.")
+
+(!begin-collecting-cold-init-forms)
+;;; This lock is seized in the compiler, and related areas -- like the
+;;; classoid/layout/class system.
+(defglobal **world-lock** nil)
+(!cold-init-forms
+ (setf **world-lock** (sb!thread:make-mutex :name "World Lock")))
+(!defun-from-collected-cold-init-forms !world-lock-cold-init)
+
+(defmacro with-world-lock (() &body body)
+ `(sb!thread:with-recursive-lock (**world-lock**)
+ ,@body))