Index: build/config-cache.jam
===================================================================
--- build/config-cache.jam	(revision 0)
+++ build/config-cache.jam	(working copy)
@@ -0,0 +1,79 @@
+# Copyright 2012 Steven Watanabe
+# Distributed under the Boost Software License, Version 1.0.
+# (See accompanying file LICENSE_1_0.txt or http://www.boost.org/LICENSE_1_0.txt)
+
+import modules ;
+import errors ;
+import regex ;
+import path ;
+import project ;
+
+rule get ( name )
+{
+    return $(.vars.$(name)) ;
+}
+
+rule set ( name : value * )
+{
+    .all-vars += $(name) ;
+    .vars.$(name) = $(value) ;
+}
+
+rule save ( )
+{
+    if $(.cache-file)
+    {
+        local target = <new-cache-file>$(.cache-file) ;
+        local contents = "# Automatically generated by Boost.Build.\n# Do not edit.\n\nmodule config-cache {\n" ;
+        for local var in $(.all-vars)
+        {
+            local transformed ;
+            for local value in $(.vars.$(var))
+            {
+                transformed += [ regex.escape $(value) : \"\\ : \\ ] ;
+            }
+            local quoted = \"$(transformed)\" ;
+            contents += "  set \"$(var)\" : $(quoted) ;\n" ;
+        }
+        contents += "}\n" ;
+        FILE_CONTENTS on $(target) = $(contents) ;
+        ALWAYS $(target) ;
+        config-cache.write $(target) ;
+        UPDATE_NOW $(target) : [ modules.peek configure : .log-fd ] : ignore-minus-n ;
+    }
+}
+
+actions write
+{
+    @($(STDOUT):E=$(FILE_CONTENTS:J=)) > "$(<)"
+}
+
+rule load ( cache-file ? )
+{
+    if $(.cache-file)
+    {
+        errors.error duplicate load of cache file ;
+    }
+    if $(cache-file)
+    {
+        cache-file = $(cache-file) ;
+    }
+    else
+    {
+        local global-build-dir = [ project.global-build-dir ] ;
+        if $(global-build-dir)
+        {
+            cache-file = [ path.join $(global-build-dir) project-cache.jam ] ;
+        }
+        else
+        {
+            local project-root = [ project.find-project-root "." ] ;
+            cache-file = [ path.join $(project-root) "project-cache.jam" ] ;
+        }
+    }
+    if [ path.exists $(cache-file) ] && ! ( --reconfigure in [ modules.peek : ARGV ] )
+    {
+        include <old-cache-file>$(cache-file) ;
+    }
+    .cache-file = $(cache-file) ;
+}

Property changes on: build/config-cache.jam
___________________________________________________________________
Added: svn:eol-style
## -0,0 +1 ##
+native
\ No newline at end of property
Added: svn:mime-type
## -0,0 +1 ##
+text/plain
\ No newline at end of property
Added: svn:keywords
## -0,0 +1 ##
+Id
\ No newline at end of property
Index: build/configure.jam
===================================================================
--- build/configure.jam	(revision 80856)
+++ build/configure.jam	(working copy)
@@ -16,6 +16,7 @@
 import property ;
 import property-set ;
 import targets ;
+import config-cache ;
 
 
 rule log-summary ( )
@@ -134,7 +135,11 @@
     {
         .$(what)-tested.$(ps) = true ;
 
-        local targets = [ targets.generate-from-reference
+        local cache-name = $(what) [ $(ps).raw ] ;
+        cache-name = $(cache-name:J=-) ;
+        local value = [ config-cache.get $(cache-name) ] ;
+        
+        local targets = [ targets.generate-from-reference 
             $(metatarget-reference) : $(project) : $(ps) ] ;
 
         local jam-targets ;
@@ -142,10 +147,24 @@
         {
             jam-targets += [ $(t).actualize ] ;
         }
-
-        if ! UPDATE_NOW in [ RULENAMES ]
+             
+        if $(value)
         {
-            # Cannot determine. Assume existence.
+            local x = [ PAD "    - $(what)" : $(.width) ] ; 
+            if $(value) = true
+            {
+                .$(what)-supported.$(ps) = yes ;
+                result = true ;
+                log-check-result "$(x) : yes (cached)" ;
+            }
+            else
+            {
+                log-check-result "$(x) : no (cached)" ;
+            }
+        }       
+        else if ! UPDATE_NOW in [ RULENAMES ]
+        {
+            # Cannot determine. Assume existance.
         }
         else
         {
@@ -162,6 +181,17 @@
                 log-check-result "$(x) : no" ;
             }
         }
+        if ! $(value)
+        {
+            if $(result)
+            {
+                config-cache.set $(cache-name) : true ;
+            }
+            else
+            {
+                config-cache.set $(cache-name) : false ;
+            }
+        }        
         return $(result) ;
     }
     else
Index: build/project.jam
===================================================================
--- build/project.jam	(revision 80856)
+++ build/project.jam	(working copy)
@@ -114,6 +114,19 @@
 }
 
 
+# Returns the path to the project root of location if
+# it exists.  Otherwise returns nothing.
+#
+rule find-project-root ( location )
+{
+    local found = [ path.glob-in-parents $(location) : $(JAMROOT) ] ;
+    if $(found)
+    {
+        return [ path.parent $(found) ] ;
+    }
+}
+
+
 # Returns the project module corresponding to the given project-id or plain
 # directory name. Returns nothing if such a project can not be found.
 #
@@ -409,6 +422,12 @@
 }
 
 
+rule global-build-dir ( )
+{
+    return $(.global-build-dir) ;
+}
+
+
 # Initialize the module for a project.
 #
 rule initialize (
Index: build-system.jam
===================================================================
--- build-system.jam	(revision 80856)
+++ build-system.jam	(working copy)
@@ -27,6 +27,7 @@
 import utility ;
 import version ;
 import virtual-target ;
+import config-cache ;
 
 
 ################################################################################
@@ -538,6 +539,8 @@
 
     version.verify-engine-version ;
 
+    config-cache.load ;
+
     load-configuration-files ;
 
     # Load explicitly specified toolset modules.
@@ -736,6 +739,7 @@
         actual-targets += [ $(t).actualize ] ;
     }
 
+    config-cache.save ;
 
     # If XML data output has been requested prepare additional rules and targets
     # so we can hook into Jam to collect build data while its building and have
Index: test/BoostBuild.py
===================================================================
--- test/BoostBuild.py	(revision 80856)
+++ test/BoostBuild.py	(working copy)
@@ -702,6 +702,7 @@
         # Boost Build's 'configure' functionality (unfinished at the time)
         # produces this file.
         self.ignore("bin/config.log")
+        self.ignore("project-cache.jam")
 
         # Compiled Python files created when running Python based Boost Build.
         self.ignore("*.pyc")