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.

7 files changed, 75 insertions, 27 deletions

diff --git a/platform/SCsub b/platform/SCsub
index 2019a30be7..0f9c2047a0 100644
--- a/platform/SCsub
+++ b/platform/SCsub
@@ -18,10 +18,13 @@ for platform in env.platform_apis:
 reg_apis_inc += '\n'
 reg_apis += '}\n\n'
 unreg_apis += '}\n'
+
+# NOTE: It is safe to generate this file here, since this is still execute serially
 with open_utf8('register_platform_apis.gen.cpp', 'w') as f:
-	f.write(reg_apis_inc)
-	f.write(reg_apis)
-	f.write(unreg_apis)
+    f.write(reg_apis_inc)
+    f.write(reg_apis)
+    f.write(unreg_apis)
+
 platform_sources.append('register_platform_apis.gen.cpp')
 
 lib = env.add_library('platform', platform_sources)
diff --git a/platform/osx/SCsub b/platform/osx/SCsub
index 4dfa46528a..5c973c30c2 100644
--- a/platform/osx/SCsub
+++ b/platform/osx/SCsub
@@ -3,14 +3,8 @@
 import os
 Import('env')
 
-def make_debug(target, source, env):
-    if (env["macports_clang"] != 'no'):
-        mpprefix = os.environ.get("MACPORTS_PREFIX", "/opt/local")
-        mpclangver = env["macports_clang"]
-        os.system(mpprefix + '/libexec/llvm-' + mpclangver + '/bin/llvm-dsymutil {0} -o {0}.dSYM'.format(target[0]))
-    else:
-        os.system('dsymutil {0} -o {0}.dSYM'.format(target[0]))
-    os.system('strip -u -r {0}'.format(target[0]))
+from platform_methods import run_in_subprocess
+import platform_osx_builders
 
 files = [
     'crash_handler_osx.mm',
@@ -25,5 +19,5 @@ files = [
 prog = env.add_program('#bin/godot', files)
 
 if (env["debug_symbols"] == "full" or env["debug_symbols"] == "yes") and env["separate_debug_symbols"]:
-    env.AddPostAction(prog, make_debug)
+    env.AddPostAction(prog, run_in_subprocess(platform_osx_builders.make_debug_osx))
 
diff --git a/platform/osx/platform_osx_builders.py b/platform/osx/platform_osx_builders.py
new file mode 100644
index 0000000000..81997f674b
--- /dev/null
+++ b/platform/osx/platform_osx_builders.py
@@ -0,0 +1,21 @@
+"""Functions used to generate source files during build time
+
+All such functions are invoked in a subprocess on Windows to prevent build flakiness.
+
+"""
+import os
+from platform_methods import subprocess_main
+
+
+def make_debug_osx(target, source, env):
+    if (env["macports_clang"] != 'no'):
+        mpprefix = os.environ.get("MACPORTS_PREFIX", "/opt/local")
+        mpclangver = env["macports_clang"]
+        os.system(mpprefix + '/libexec/llvm-' + mpclangver + '/bin/llvm-dsymutil {0} -o {0}.dSYM'.format(target[0]))
+    else:
+        os.system('dsymutil {0} -o {0}.dSYM'.format(target[0]))
+    os.system('strip -u -r {0}'.format(target[0]))
+
+
+if __name__ == '__main__':
+    subprocess_main(globals())
diff --git a/platform/windows/SCsub b/platform/windows/SCsub
index ed3827353d..53ed3bf887 100644
--- a/platform/windows/SCsub
+++ b/platform/windows/SCsub
@@ -3,15 +3,8 @@
 import os
 Import('env')
 
-def make_debug_mingw(target, source, env):
-    mingw_prefix = ""
-    if (env["bits"] == "32"):
-        mingw_prefix = env["mingw_prefix_32"]
-    else:
-        mingw_prefix = env["mingw_prefix_64"]
-    os.system(mingw_prefix + 'objcopy --only-keep-debug {0} {0}.debugsymbols'.format(target[0]))
-    os.system(mingw_prefix + 'strip --strip-debug --strip-unneeded {0}'.format(target[0]))
-    os.system(mingw_prefix + 'objcopy --add-gnu-debuglink={0}.debugsymbols {0}'.format(target[0]))
+from platform_methods import run_in_subprocess
+import platform_windows_builders
 
 common_win = [
     "context_gl_win.cpp",
@@ -40,4 +33,4 @@ if env['vsproj']:
 
 if not os.getenv("VCINSTALLDIR"):
     if (env["debug_symbols"] == "full" or env["debug_symbols"] == "yes") and env["separate_debug_symbols"]:
-        env.AddPostAction(prog, make_debug_mingw)
+        env.AddPostAction(prog, run_in_subprocess(platform_windows_builders.make_debug_mingw))
diff --git a/platform/windows/platform_windows_builders.py b/platform/windows/platform_windows_builders.py
new file mode 100644
index 0000000000..a1ad3b8b50
--- /dev/null
+++ b/platform/windows/platform_windows_builders.py
@@ -0,0 +1,22 @@
+"""Functions used to generate source files during build time
+
+All such functions are invoked in a subprocess on Windows to prevent build flakiness.
+
+"""
+import os
+from platform_methods import subprocess_main
+
+
+def make_debug_mingw(target, source, env):
+    mingw_prefix = ""
+    if (env["bits"] == "32"):
+        mingw_prefix = env["mingw_prefix_32"]
+    else:
+        mingw_prefix = env["mingw_prefix_64"]
+    os.system(mingw_prefix + 'objcopy --only-keep-debug {0} {0}.debugsymbols'.format(target[0]))
+    os.system(mingw_prefix + 'strip --strip-debug --strip-unneeded {0}'.format(target[0]))
+    os.system(mingw_prefix + 'objcopy --add-gnu-debuglink={0}.debugsymbols {0}'.format(target[0]))
+
+
+if __name__ == '__main__':
+    subprocess_main(globals())
diff --git a/platform/x11/SCsub b/platform/x11/SCsub
index d0f77892ef..d3901eb798 100644
--- a/platform/x11/SCsub
+++ b/platform/x11/SCsub
@@ -3,10 +3,8 @@
 import os
 Import('env')
 
-def make_debug(target, source, env):
-    os.system('objcopy --only-keep-debug {0} {0}.debugsymbols'.format(target[0]))
-    os.system('strip --strip-debug --strip-unneeded {0}'.format(target[0]))
-    os.system('objcopy --add-gnu-debuglink={0}.debugsymbols {0}'.format(target[0]))
+from platform_methods import run_in_subprocess
+import platform_x11_builders
 
 common_x11 = [
     "context_gl_x11.cpp",
@@ -20,4 +18,4 @@ common_x11 = [
 prog = env.add_program('#bin/godot', ['godot_x11.cpp'] + common_x11)
 
 if (env["debug_symbols"] == "full" or env["debug_symbols"] == "yes") and env["separate_debug_symbols"]:
-    env.AddPostAction(prog, make_debug)
+    env.AddPostAction(prog, run_in_subprocess(platform_x11_builders.make_debug_x11))
diff --git a/platform/x11/platform_x11_builders.py b/platform/x11/platform_x11_builders.py
new file mode 100644
index 0000000000..5ff0c6fb14
--- /dev/null
+++ b/platform/x11/platform_x11_builders.py
@@ -0,0 +1,17 @@
+"""Functions used to generate source files during build time
+
+All such functions are invoked in a subprocess on Windows to prevent build flakiness.
+
+"""
+import os
+from platform_methods import subprocess_main
+
+
+def make_debug_x11(target, source, env):
+    os.system('objcopy --only-keep-debug {0} {0}.debugsymbols'.format(target[0]))
+    os.system('strip --strip-debug --strip-unneeded {0}'.format(target[0]))
+    os.system('objcopy --add-gnu-debuglink={0}.debugsymbols {0}'.format(target[0]))
+
+
+if __name__ == '__main__':
+    subprocess_main(globals())