diff -r eda6988c0d81 -r f08d439fab8c src/cpu/zero/vm/globals_zero.hpp
--- a/src/cpu/zero/vm/globals_zero.hpp	Tue Sep 20 23:50:16 2011 -0700
+++ b/src/cpu/zero/vm/globals_zero.hpp	Sun Sep 25 16:03:29 2011 -0700
@@ -52,7 +52,11 @@
 define_pd_global(bool,  RewriteBytecodes,     true);
 define_pd_global(bool,  RewriteFrequentPairs, true);
 
+#ifdef _ALLBSD_SOURCE
+define_pd_global(bool,  UseMembar,            true);
+#else
 define_pd_global(bool,  UseMembar,            false);
+#endif
 
 // GC Ergo Flags
 define_pd_global(intx, CMSYoungGenPerWorker, 16*M);  // default max size of CMS young gen, per GC worker thread