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, 25 insertions, 23 deletions

diff --git a/core/SCsub b/core/SCsub
index c508ecc37e..c8e2e10b9f 100644
--- a/core/SCsub
+++ b/core/SCsub
@@ -2,7 +2,9 @@
 
 Import('env')
 
-import methods
+import core_builders
+import make_binders
+from platform_methods import run_in_subprocess
 
 env.core_sources = []
 
@@ -21,7 +23,7 @@ gd_cpp += gd_inc
 gd_cpp += "void ProjectSettings::register_global_defaults() {\n" + gd_call + "\n}\n"
 
 with open("global_defaults.gen.cpp", "w") as f:
-	f.write(gd_cpp)
+    f.write(gd_cpp)
 
 
 # Generate AES256 script encryption key
@@ -48,26 +50,27 @@ if ("SCRIPT_AES256_ENCRYPTION_KEY" in os.environ):
         txt = "0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0"
         print("Invalid AES256 encryption key, not 64 bits hex: " + e)
 
+# NOTE: It is safe to generate this file here, since this is still executed serially
 with open("script_encryption_key.gen.cpp", "w") as f:
-	f.write("#include \"project_settings.h\"\nuint8_t script_encryption_key[32]={" + txt + "};\n")
+    f.write("#include \"project_settings.h\"\nuint8_t script_encryption_key[32]={" + txt + "};\n")
 
 
 # Add required thirdparty code. Header paths are hardcoded, we don't need to append
 # to the include path (saves a few chars on the compiler invocation for touchy MSVC...)
 thirdparty_dir = "#thirdparty/misc/"
 thirdparty_sources = [
-	# C sources
-	"base64.c",
-	"fastlz.c",
-	"sha256.c",
-	"smaz.c",
-
-	# C++ sources
-	"aes256.cpp",
-	"hq2x.cpp",
-	"md5.cpp",
-	"pcg.cpp",
-	"triangulator.cpp",
+    # C sources
+    "base64.c",
+    "fastlz.c",
+    "sha256.c",
+    "smaz.c",
+
+    # C++ sources
+    "aes256.cpp",
+    "hq2x.cpp",
+    "md5.cpp",
+    "pcg.cpp",
+    "triangulator.cpp",
 ]
 thirdparty_sources = [thirdparty_dir + file for file in thirdparty_sources]
 env.add_source_files(env.core_sources, thirdparty_sources)
@@ -76,9 +79,9 @@ env.add_source_files(env.core_sources, thirdparty_sources)
 # However, our version has some custom modifications, so it won't compile with the system one
 thirdparty_minizip_dir = "#thirdparty/minizip/"
 thirdparty_minizip_sources = [
-	"ioapi.c",
-	"unzip.c",
-	"zip.c",
+    "ioapi.c",
+    "unzip.c",
+    "zip.c",
 ]
 thirdparty_minizip_sources = [thirdparty_minizip_dir + file for file in thirdparty_minizip_sources]
 env.add_source_files(env.core_sources, thirdparty_minizip_sources)
@@ -92,20 +95,19 @@ env.add_source_files(env.core_sources, "*.cpp")
 
 
 # Make binders
-import make_binders
-env.CommandNoCache(['method_bind.gen.inc', 'method_bind_ext.gen.inc'], 'make_binders.py', make_binders.run)
+env.CommandNoCache(['method_bind.gen.inc', 'method_bind_ext.gen.inc'], 'make_binders.py', run_in_subprocess(make_binders.run))
 
 # Authors
 env.Depends('#core/authors.gen.h', "../AUTHORS.md")
-env.CommandNoCache('#core/authors.gen.h', "../AUTHORS.md", methods.make_authors_header)
+env.CommandNoCache('#core/authors.gen.h', "../AUTHORS.md", run_in_subprocess(core_builders.make_authors_header))
 
 # Donors
 env.Depends('#core/donors.gen.h', "../DONORS.md")
-env.CommandNoCache('#core/donors.gen.h', "../DONORS.md", methods.make_donors_header)
+env.CommandNoCache('#core/donors.gen.h', "../DONORS.md", run_in_subprocess(core_builders.make_donors_header))
 
 # License
 env.Depends('#core/license.gen.h', ["../COPYRIGHT.txt", "../LICENSE.txt"])
-env.CommandNoCache('#core/license.gen.h', ["../COPYRIGHT.txt", "../LICENSE.txt"], methods.make_license_header)
+env.CommandNoCache('#core/license.gen.h', ["../COPYRIGHT.txt", "../LICENSE.txt"], run_in_subprocess(core_builders.make_license_header))
 
 # Chain load SCsubs
 SConscript('os/SCsub')