Re: thread model for mxe-octave build

[John W. Eaton]

On 02/22/2018 12:02 PM, JohnD wrote:
> > -----Original Message-----
> > From: John W. Eaton [mailto:address@hidden
> > Sent: Thursday, February 22, 2018 11:44 AM
> > To: John Donoghue; Octave Maintainers List
> > Cc: address@hidden
> > Subject: thread model for mxe-octave build
> >
> > I had someone ask why C++11 threads (mutext, condition_variable_any) wasn't
> > working with .oct files built with Octave 4.2.1.  After a little searching, I 
> > found
> > that we are configuring GCC with
> > --enable-threads=win32 instead of --enable-threads=posix.  Apparently the
> > latter is required to enable C++11 thread features.  Is there any reason to not
> > use --enable-threads=posix by default in our builds?  I tried building 
> > native-gcc
> > with this option and it allowed my test program to compile but I don't know
> > whether there might be other problems.  From what I hve read, it seems that
> > even if GCC is built with this option you can still use Windows threading
> > features directly.  I've seen some mention of performance issues "in some
> > situations" but no explanation of what that might be.
> >
> > jwe
>
> No reason I know of except that mxe was/is using win32

I tried changing the following change:

diff --git a/src/build-gcc.mk b/src/build-gcc.mk
--- a/src/build-gcc.mk
+++ b/src/build-gcc.mk
@@ -31,7 +31,7 @@ ifeq ($(MXE_SYSTEM),mingw)
     --disable-nls \
     --without-x \
     --disable-win32-registry \
-    --enable-threads=win32
+    --enable-threads=posix
   ifneq ($(TARGET),x86_64-w64-mingw32)
     $(PKG)_SYSDEP_CONFIGURE_OPTIONS += \
     --libdir='$(BUILD_TOOLS_PREFIX)/lib' \
diff --git a/src/native-gcc.mk b/src/native-gcc.mk
--- a/src/native-gcc.mk
+++ b/src/native-gcc.mk
@@ -25,7 +25,7 @@ ifeq ($(MXE_SYSTEM),mingw)
     --without-x \
     --disable-win32-registry \
     --with-native-system-header-dir='$(HOST_PREFIX)/include' \
-    --enable-threads=win32
+    --enable-threads=posix
   ifneq ($(ENABLE_WINDOWS_64),yes)
     $(PKG)_SYSDEP_CONFIGURE_OPTIONS += \
       $(ENABLE_SHARED_OR_STATIC) \

The build-gcc target fails because pthread.h is not available:

In file included from 
/home/jwe/build/mxe-octave-w64-32-posix/tmp-build-gcc/gcc-7.2.0/libgcc/gthr.h:148:0,
                 from 
/home/jwe/build/mxe-octave-w64-32-posix/tmp-build-gcc/gcc-7.2.0/libgcc/libgcov-interface.c:27:
./gthr-default.h:35:10: fatal error: pthread.h: No such file or directory
 #include <pthread.h>
          ^~~~~~~~~~~
compilation terminated.
Makefile:915: recipe for target '_gcov_dump.o' failed
make[6]: *** [_gcov_dump.o] Error 1

Maybe this is just a dependency ordering issue, but I'm not sure how to 
fix it.

Using --enable-threads=win32 for build-gcc and --enable-threads=posix 
for native-gcc allows the build to succeed, but I'm not sure that is a 
proper configuration.  Even if it is, we will also need to use posix 
threads for build-gcc if we want to start using C++11 threading features 
in Octave itself.  Any ideas about how to build a GCC cross compiler for 
Windows that has the posix thread model enabled?

jwe