Only create a default Environment when asked to. (Chad Austin)

5 files changed, 16 insertions, 7 deletions

diff --git a/src/CHANGES.txt b/src/CHANGES.txt
index abbf744..33e481d 100644
--- a/src/CHANGES.txt
+++ b/src/CHANGES.txt
@@ -17,6 +17,9 @@ RELEASE 0.XX - XXX
   - Give a Value Nodes a timestamp of the system time when they're
     created, so they'll work when using timestamp-based signatures.
 
+  - Add a DefaultEnvironment() function that only creates a default
+    environment on-demand (for fetching source files, e.g.).
+
   From Steven Knight:
 
   - Tighten up the scons -H help output.
diff --git a/src/engine/SCons/Defaults.py b/src/engine/SCons/Defaults.py
index e2bb3b4..aa0fbd9 100644
--- a/src/engine/SCons/Defaults.py
+++ b/src/engine/SCons/Defaults.py
@@ -44,6 +44,7 @@ import string
 
 import SCons.Action
 import SCons.Builder
+import SCons.Environment
 import SCons.Node.Alias
 import SCons.Node.FS
 import SCons.Scanner.C
@@ -56,6 +57,15 @@ import SCons.Scanner.Prog
 # interface.
 _default_env = None
 
+# Lazily instantiate the default environment so the overhead of creating
+# it doesn't apply when it's not needed.
+def DefaultEnvironment():
+    global _default_env
+    if not _default_env:
+        _default_env = SCons.Environment.Environment()
+    return _default_env
+
+
 def alias_builder(env, target, source):
     pass
 
diff --git a/src/engine/SCons/Node/FS.py b/src/engine/SCons/Node/FS.py
index 1f88330..a17cee0 100644
--- a/src/engine/SCons/Node/FS.py
+++ b/src/engine/SCons/Node/FS.py
@@ -168,7 +168,7 @@ def get_DefaultSCCSBuilder():
         import SCons.Builder
         import SCons.Defaults
         DefaultSCCSBuilder = SCons.Builder.Builder(action = '$SCCSCOM',
-                                                   env = SCons.Defaults._default_env)
+                                                   env = SCons.Defaults.DefaultEnvironment())
     return DefaultSCCSBuilder
 
 def get_DefaultRCSBuilder():
@@ -177,7 +177,7 @@ def get_DefaultRCSBuilder():
         import SCons.Builder
         import SCons.Defaults
         DefaultRCSBuilder = SCons.Builder.Builder(action = '$RCS_COCOM',
-                                                  env = SCons.Defaults._default_env)
+                                                  env = SCons.Defaults.DefaultEnvironment())
     return DefaultRCSBuilder
 
 #
diff --git a/src/engine/SCons/Script/SConscript.py b/src/engine/SCons/Script/SConscript.py
index 5f7f4b5..313a3f2 100644
--- a/src/engine/SCons/Script/SConscript.py
+++ b/src/engine/SCons/Script/SConscript.py
@@ -513,7 +513,6 @@ def BuildDefaultGlobals():
     """
 
     globals = {}
-    globals['_default_env']      = SCons.Defaults._default_env
     globals['Action']            = SCons.Action.Action
     globals['AddPostAction']     = AddPostAction
     globals['AddPreAction']      = AddPreAction
@@ -526,6 +525,7 @@ def BuildDefaultGlobals():
     globals['Configure']         = SCons.SConf.SConf
     globals['CScan']             = SCons.Defaults.CScan
     globals['Default']           = Default
+    globals['DefaultEnvironment'] = SCons.Defaults.DefaultEnvironment
     globals['Dir']               = SCons.Node.FS.default_fs.Dir
     globals['EnsurePythonVersion'] = EnsurePythonVersion
     globals['EnsureSConsVersion'] = EnsureSConsVersion
diff --git a/src/engine/SCons/Script/__init__.py b/src/engine/SCons/Script/__init__.py
index fe56568..c171a91 100644
--- a/src/engine/SCons/Script/__init__.py
+++ b/src/engine/SCons/Script/__init__.py
@@ -750,10 +750,6 @@ def _main(args, parser):
 
     SCons.Node.FS.default_fs.set_toplevel_dir(os.getcwd())
 
-    # Now that the top-level directory has been set,
-    # we can initialize the default Environment.
-    SCons.Defaults._default_env = SCons.Environment.Environment()
-
     scripts = []
     if options.file:
         scripts.extend(options.file)