X-Git-Url: http://repo.macrolet.net/gitweb/?a=blobdiff_plain;f=base-target-features.lisp-expr;h=5b97f7295761437ba5dc5e439a4d482f78295d0e;hb=78e261f4ad7a0f3a0cf805ecc0052f0ccbf8fcd0;hp=207a04fd36429b20f059c3b72cd99ab9bc74eca2;hpb=5930ee54090c03d242c70716683b12b95d74a089;p=sbcl.git

diff --git a/base-target-features.lisp-expr b/base-target-features.lisp-expr
index 207a04f..5b97f72 100644
--- a/base-target-features.lisp-expr
+++ b/base-target-features.lisp-expr
@@ -159,16 +159,21 @@
  ;; Note that no consistent effort to audit the SBCL library code for
  ;; thread safety has been performed, so caveat executor.
  ; :sb-thread
+
+ ;; Kernel support for futexes (so-called "fast userspace mutexes") is
+ ;; available in Linux 2.6 and some versions of 2.4 (Red Hat vendor
+ ;; kernels, possibly other vendors too).  We can take advantage of
+ ;; these to do faster and probably more reliable mutex and condition
+ ;; variable support.  An SBCL built with this feature will fall back
+ ;; to the old system if the futex() syscall is not available at
+ ;; runtime
+ ; :sb-futex
  
  ;; This affects the definition of a lot of things in bignum.lisp. It
  ;; doesn't seem to be documented anywhere what systems it might apply
  ;; to. It doesn't seem to be needed for X86 systems anyway.
  ; :32x16-divide
 
- ;; This is probably true for some processor types, but not X86. It
- ;; affects a lot of floating point code.
- ; :negative-zero-is-not-zero
-
  ;; This is set in classic CMU CL, and presumably there it means
  ;; that the floating point arithmetic implementation
  ;; conforms to IEEE's standard. Here it definitely means that the