Merge pull request SCons#4464 from acmorrow/flip-sched-default

Make the NewParallel scheduler the default, even for -j1 builds

Author: bdbaddog

CHANGES.txt

@@ -56,6 +56,16 @@ RELEASE  VERSION/DATE TO BE FILLED IN LATER
   From Prabhu S. Khalsa:
     - Fix typo in user documentation (issue #4458)
 
+  From Andrew Morrow:
+    - The NewParallel scheduler is now the default, the `tm_v2` flag is removed,
+      and the old scheduler is opt-in under `--experimental=legacy_sched`. Additionally,
+      the new scheduler is now used for -j1 builds as well.
+    - A python interpreter with support for the `threading` package is now required,
+      and this is enforced on startup. SCons currently sets its minimum supported
+      Python to 3.6, and it was not until Python 3.7 where `threading` became
+      default supported. In practice, we expect most real world Python 3.6 deployments
+      will have `threading` support enabled, so this will not be an issue.
+
   From Mats Wichmann:
     - Add support for Python 3.13 (as of alpha 2). So far only affects
       expected bytecodes in ActionTests.py.
@@ -7950,4 +7960,3 @@ A brief overview of important functionality available in release 0.01:
   - Linux packages available in RPM and Debian format.
 
   - Windows installer available.
-

RELEASE.txt

@@ -33,6 +33,7 @@ CHANGED/ENHANCED EXISTING FUNCTIONALITY
   that the generated function argument list matches the function's
   prototype when including a header file. Fixes GH Issue #4320
 - Now supports pre-release Python 3.13
+- Support for Python versions without support for the `threading` package has been removed
 
 FIXES
 -----

SCons/SConf.py

@@ -251,10 +251,9 @@ def display_cached_string(self, bi) -> None:
     def failed(self):
         # check, if the reason was a ConfigureDryRunError or a
         # ConfigureCacheError and if yes, reraise the exception
-        exc_type = self.exc_info()[0]
+        exc_type, exc, _ = self.exc_info()
         if issubclass(exc_type, SConfError):
-            # TODO pylint E0704: bare raise not inside except
-            raise
+            raise exc
         elif issubclass(exc_type, SCons.Errors.BuildError):
             # we ignore Build Errors (occurs, when a test doesn't pass)
             # Clear the exception to prevent the contained traceback

SCons/Script/Main.py

@@ -1447,6 +1447,13 @@ def main() -> None:
         sys.stderr.write("scons: *** Minimum Python version is %d.%d.%d\n" %minimum_python_version)
         sys.exit(1)
 
+    try:
+        import threading
+    except ImportError:
+        msg = "scons: *** SCons version %s requires a Python interpreter with support for the `threading` package"
+        sys.stderr.write(msg % SConsVersion)
+        sys.exit(1)
+
     parts = ["SCons by Steven Knight et al.:\n"]
     try:
         import SCons

SCons/Script/SConsOptions.py

@@ -40,7 +40,7 @@
 
 diskcheck_all = SCons.Node.FS.diskcheck_types()
 
-experimental_features = {'warp_speed', 'transporter', 'ninja', 'tm_v2'}
+experimental_features = {'warp_speed', 'transporter', 'ninja', 'legacy_sched'}
 
 
 def diskcheck_convert(value):