Running builder (content generator) functions in subprocesses on Windows

- Refactored all builder (make_*) functions into separate Python modules along to the build tree
- Introduced utility function to wrap all invocations on Windows, but does not change it elsewhere
- Introduced stub to use the builders module as a stand alone script and invoke a selected function

There is a problem with file handles related to writing generated content (*.gen.h and *.gen.cpp)
on Windows, which randomly causes a SHARING VIOLATION error to the compiler resulting in flaky
builds. Running all such content generators in a new subprocess instead of directly inside the
build script works around the issue.

Yes, I tried the multiprocessing module. It did not work due to conflict with SCons on cPickle.
Suggested workaround did not fully work either.

Using the run_in_subprocess wrapper on osx and x11 platforms as well for consistency. In case of
running a cross-compilation on Windows they would still be used, but likely it will not happen
in practice. What counts is that the build itself is running on which platform, not the target
platform.

Some generated files are written directly in an SConstruct or SCsub file, before the parallel build starts. They don't need to be written in a subprocess, apparently, so I left them as is.

1 files changed, 4 insertions, 2 deletions

diff --git a/SConstruct b/SConstruct
index 1135f7a3bd..2cc486fd1b 100644
--- a/SConstruct
+++ b/SConstruct
@@ -8,6 +8,8 @@ import os.path
 import glob
 import sys
 import methods
+import gles_builders
+from platform_methods import run_in_subprocess
 
 # scan possible build platforms
 
@@ -444,8 +446,8 @@ if selected_platform in platform_list:
         methods.no_verbose(sys, env)
 
     if (not env["platform"] == "server"): # FIXME: detect GLES3
-        env.Append( BUILDERS = { 'GLES3_GLSL' : env.Builder(action = methods.build_gles3_headers, suffix = 'glsl.gen.h', src_suffix = '.glsl') } )
-        env.Append( BUILDERS = { 'GLES2_GLSL' : env.Builder(action = methods.build_gles2_headers, suffix = 'glsl.gen.h', src_suffix = '.glsl') } )
+        env.Append(BUILDERS = { 'GLES3_GLSL' : env.Builder(action=run_in_subprocess(gles_builders.build_gles3_headers), suffix='glsl.gen.h', src_suffix='.glsl')})
+        env.Append(BUILDERS = { 'GLES2_GLSL' : env.Builder(action=run_in_subprocess(gles_builders.build_gles2_headers), suffix='glsl.gen.h', src_suffix='.glsl')})
 
     scons_cache_path = os.environ.get("SCONS_CACHE")
     if scons_cache_path != None: