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.

2 files changed, 136 insertions, 126 deletions

diff --git a/main/SCsub b/main/SCsub
index 0692175799..9af102600e 100644
--- a/main/SCsub
+++ b/main/SCsub
@@ -1,128 +1,8 @@
 #!/usr/bin/env python
 
 Import('env')
-from compat import byte_to_str
-from collections import OrderedDict
-
-def make_splash(target, source, env):
-
-    src = source[0].srcnode().abspath
-    dst = target[0].srcnode().abspath
-
-    with open(src, "rb") as f:
-        buf = f.read()
-
-    with open(dst, "w") as g:
-        g.write("/* THIS FILE IS GENERATED DO NOT EDIT */\n")
-        g.write("#ifndef BOOT_SPLASH_H\n")
-        g.write("#define BOOT_SPLASH_H\n")
-        g.write('static const Color boot_splash_bg_color = Color::html("#232323");\n')
-        g.write("static const unsigned char boot_splash_png[] = {\n")
-        for i in range(len(buf)):
-            g.write(byte_to_str(buf[i]) + ",\n")
-        g.write("};\n")
-        g.write("#endif")
-
-
-def make_splash_editor(target, source, env):
-
-    src = source[0].srcnode().abspath
-    dst = target[0].srcnode().abspath
-
-    with open(src, "rb") as f:
-        buf = f.read()
-
-    with open(dst, "w") as g:
-        g.write("/* THIS FILE IS GENERATED DO NOT EDIT */\n")
-        g.write("#ifndef BOOT_SPLASH_EDITOR_H\n")
-        g.write("#define BOOT_SPLASH_EDITOR_H\n")
-        g.write('static const Color boot_splash_editor_bg_color = Color::html("#232323");\n')
-        g.write("static const unsigned char boot_splash_editor_png[] = {\n")
-        for i in range(len(buf)):
-            g.write(byte_to_str(buf[i]) + ",\n")
-        g.write("};\n")
-        g.write("#endif")
-
-
-def make_app_icon(target, source, env):
-
-    src = source[0].srcnode().abspath
-    dst = target[0].srcnode().abspath
-
-    with open(src, "rb") as f:
-        buf = f.read()
-
-    with open(dst, "w") as g:
-        g.write("/* THIS FILE IS GENERATED DO NOT EDIT */\n")
-        g.write("#ifndef APP_ICON_H\n")
-        g.write("#define APP_ICON_H\n")
-        g.write("static const unsigned char app_icon_png[] = {\n")
-        for i in range(len(buf)):
-            g.write(byte_to_str(buf[i]) + ",\n")
-        g.write("};\n")
-        g.write("#endif")
-
-def make_default_controller_mappings(target, source, env):
-    dst = target[0].srcnode().abspath
-    g = open(dst, "w")
-
-    g.write("/* THIS FILE IS GENERATED DO NOT EDIT */\n")
-    g.write("#include \"default_controller_mappings.h\"\n")
-    g.write("#include \"typedefs.h\"\n")
-
-    # ensure mappings have a consistent order
-    platform_mappings = OrderedDict()
-    for src in source:
-        src_path = src.srcnode().abspath
-        with open(src_path, "r") as f:
-            # read mapping file and skip header
-            mapping_file_lines = f.readlines()[2:]
-
-        current_platform = None
-        for line in mapping_file_lines:
-            if not line:
-                continue
-            line = line.strip()
-            if len(line) == 0:
-                continue
-            if line[0] == "#":
-                current_platform = line[1:].strip()
-                if current_platform not in platform_mappings:
-                    platform_mappings[current_platform] = {}
-            elif current_platform:
-                line_parts = line.split(",")
-                guid = line_parts[0]
-                if guid in platform_mappings[current_platform]:
-                    g.write("// WARNING - DATABASE {} OVERWROTE PRIOR MAPPING: {} {}\n".format(src_path, current_platform, platform_mappings[current_platform][guid]))
-                valid_mapping = True
-                for input_map in line_parts[2:]:
-                    if "+" in input_map or "-" in input_map or "~" in input_map:
-                        g.write("// WARNING - DISCARDED UNSUPPORTED MAPPING TYPE FROM DATABASE {}: {} {}\n".format(src_path, current_platform, line))
-                        valid_mapping = False
-                        break
-                if valid_mapping:
-                    platform_mappings[current_platform][guid] = line
-            
-    platform_variables = {
-        "Linux": "#if X11_ENABLED",
-        "Windows": "#ifdef WINDOWS_ENABLED",
-        "Mac OS X": "#ifdef OSX_ENABLED",
-        "Android": "#if defined(__ANDROID__)",
-        "iOS": "#ifdef IPHONE_ENABLED",
-        "Javascript": "#ifdef JAVASCRIPT_ENABLED",
-        "UWP": "#ifdef UWP_ENABLED",
-    }
-
-    g.write("const char* DefaultControllerMappings::mappings[] = {\n")
-    for platform, mappings in platform_mappings.items():
-        variable = platform_variables[platform]
-        g.write("{}\n".format(variable))
-        for mapping in mappings.values():
-            g.write("\t\"{}\",\n".format(mapping))
-        g.write("#endif\n")
-
-    g.write("\tNULL\n};\n")
-    g.close()
+from platform_methods import run_in_subprocess
+import main_builders
 
 env.main_sources = []
 env.add_source_files(env.main_sources, "*.cpp")
@@ -131,20 +11,20 @@ env.add_source_files(env.main_sources, "*.cpp")
 controller_databases = ["#main/gamecontrollerdb.txt", "#main/gamecontrollerdb_205.txt", "#main/gamecontrollerdb_204.txt", "#main/godotcontrollerdb.txt"]
 
 env.Depends("#main/default_controller_mappings.gen.cpp", controller_databases)
-env.CommandNoCache("#main/default_controller_mappings.gen.cpp", controller_databases, make_default_controller_mappings)
+env.CommandNoCache("#main/default_controller_mappings.gen.cpp", controller_databases, run_in_subprocess(main_builders.make_default_controller_mappings))
 
 env.main_sources.append("#main/default_controller_mappings.gen.cpp")
 
 Export('env')
 
 env.Depends("#main/splash.gen.h", "#main/splash.png")
-env.CommandNoCache("#main/splash.gen.h", "#main/splash.png", make_splash)
+env.CommandNoCache("#main/splash.gen.h", "#main/splash.png", run_in_subprocess(main_builders.make_splash))
 
 env.Depends("#main/splash_editor.gen.h", "#main/splash_editor.png")
-env.CommandNoCache("#main/splash_editor.gen.h", "#main/splash_editor.png", make_splash_editor)
+env.CommandNoCache("#main/splash_editor.gen.h", "#main/splash_editor.png", run_in_subprocess(main_builders.make_splash_editor))
 
 env.Depends("#main/app_icon.gen.h", "#main/app_icon.png")
-env.CommandNoCache("#main/app_icon.gen.h", "#main/app_icon.png", make_app_icon)
+env.CommandNoCache("#main/app_icon.gen.h", "#main/app_icon.png", run_in_subprocess(main_builders.make_app_icon))
 
 SConscript('tests/SCsub')
 
diff --git a/main/main_builders.py b/main/main_builders.py
new file mode 100644
index 0000000000..6d45768493
--- /dev/null
+++ b/main/main_builders.py
@@ -0,0 +1,130 @@
+"""Functions used to generate source files during build time
+
+All such functions are invoked in a subprocess on Windows to prevent build flakiness.
+
+"""
+from platform_methods import subprocess_main
+from compat import byte_to_str
+from collections import OrderedDict
+
+
+def make_splash(target, source, env):
+    src = source[0]
+    dst = target[0]
+
+    with open(src, "rb") as f:
+        buf = f.read()
+
+    with open(dst, "w") as g:
+        g.write("/* THIS FILE IS GENERATED DO NOT EDIT */\n")
+        g.write("#ifndef BOOT_SPLASH_H\n")
+        g.write("#define BOOT_SPLASH_H\n")
+        g.write('static const Color boot_splash_bg_color = Color::html("#232323");\n')
+        g.write("static const unsigned char boot_splash_png[] = {\n")
+        for i in range(len(buf)):
+            g.write(byte_to_str(buf[i]) + ",\n")
+        g.write("};\n")
+        g.write("#endif")
+
+
+def make_splash_editor(target, source, env):
+    src = source[0]
+    dst = target[0]
+
+    with open(src, "rb") as f:
+        buf = f.read()
+
+    with open(dst, "w") as g:
+        g.write("/* THIS FILE IS GENERATED DO NOT EDIT */\n")
+        g.write("#ifndef BOOT_SPLASH_EDITOR_H\n")
+        g.write("#define BOOT_SPLASH_EDITOR_H\n")
+        g.write('static const Color boot_splash_editor_bg_color = Color::html("#232323");\n')
+        g.write("static const unsigned char boot_splash_editor_png[] = {\n")
+        for i in range(len(buf)):
+            g.write(byte_to_str(buf[i]) + ",\n")
+        g.write("};\n")
+        g.write("#endif")
+
+
+def make_app_icon(target, source, env):
+    src = source[0]
+    dst = target[0]
+
+    with open(src, "rb") as f:
+        buf = f.read()
+
+    with open(dst, "w") as g:
+        g.write("/* THIS FILE IS GENERATED DO NOT EDIT */\n")
+        g.write("#ifndef APP_ICON_H\n")
+        g.write("#define APP_ICON_H\n")
+        g.write("static const unsigned char app_icon_png[] = {\n")
+        for i in range(len(buf)):
+            g.write(byte_to_str(buf[i]) + ",\n")
+        g.write("};\n")
+        g.write("#endif")
+
+
+def make_default_controller_mappings(target, source, env):
+    dst = target[0]
+    g = open(dst, "w")
+
+    g.write("/* THIS FILE IS GENERATED DO NOT EDIT */\n")
+    g.write("#include \"default_controller_mappings.h\"\n")
+    g.write("#include \"typedefs.h\"\n")
+
+    # ensure mappings have a consistent order
+    platform_mappings = OrderedDict()
+    for src_path in source:
+        with open(src_path, "r") as f:
+            # read mapping file and skip header
+            mapping_file_lines = f.readlines()[2:]
+
+        current_platform = None
+        for line in mapping_file_lines:
+            if not line:
+                continue
+            line = line.strip()
+            if len(line) == 0:
+                continue
+            if line[0] == "#":
+                current_platform = line[1:].strip()
+                if current_platform not in platform_mappings:
+                    platform_mappings[current_platform] = {}
+            elif current_platform:
+                line_parts = line.split(",")
+                guid = line_parts[0]
+                if guid in platform_mappings[current_platform]:
+                    g.write("// WARNING - DATABASE {} OVERWROTE PRIOR MAPPING: {} {}\n".format(src_path, current_platform, platform_mappings[current_platform][guid]))
+                valid_mapping = True
+                for input_map in line_parts[2:]:
+                    if "+" in input_map or "-" in input_map or "~" in input_map:
+                        g.write("// WARNING - DISCARDED UNSUPPORTED MAPPING TYPE FROM DATABASE {}: {} {}\n".format(src_path, current_platform, line))
+                        valid_mapping = False
+                        break
+                if valid_mapping:
+                    platform_mappings[current_platform][guid] = line
+
+    platform_variables = {
+        "Linux": "#if X11_ENABLED",
+        "Windows": "#ifdef WINDOWS_ENABLED",
+        "Mac OS X": "#ifdef OSX_ENABLED",
+        "Android": "#if defined(__ANDROID__)",
+        "iOS": "#ifdef IPHONE_ENABLED",
+        "Javascript": "#ifdef JAVASCRIPT_ENABLED",
+        "UWP": "#ifdef UWP_ENABLED",
+    }
+
+    g.write("const char* DefaultControllerMappings::mappings[] = {\n")
+    for platform, mappings in platform_mappings.items():
+        variable = platform_variables[platform]
+        g.write("{}\n".format(variable))
+        for mapping in mappings.values():
+            g.write("\t\"{}\",\n".format(mapping))
+        g.write("#endif\n")
+
+    g.write("\tNULL\n};\n")
+    g.close()
+
+
+if __name__ == '__main__':
+    subprocess_main(globals())