SMP problems with examples/Makefile.am

[Bo Forslund <bo dot forslund at abc dot se>]

Hello!


It is SMP problems with the Makefile in the examples dir.

I tested 30-40 compiles of the examples on a single-CPU box using  a
Makefile built by the original Makefile.am containing the lines

foo-glue.c: foo.defs
 build-guile-gtk glue $< >tmp && mv tmp $@

main.c: foo.defs
 build-guile-gtk main $< >tmp && mv tmp $@

And it just worked. Every time.


On the dual-CPU box it failed most of the times with really odd result.
Sometimes the build created a main.c identical to foo-glue.c.  Sometimes
the foo-glue.c or main.c was created with a couple of thousand
NULL characters (displayed as ^@ in emacs) and a chopped off line with
the extern sgtk_.... vars, and the rest of foo-glue.c as it should look.

 something like

/* Generated by build-guile-gtk from "foo.defs".  Do not edit. */

#include <libguile.h>
#include <guile-gtk.h>
#include <foo.h>


^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@
^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@
several thousands of ^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@
info sgtk_gdk_cap_style_info;
extern sgtk_enum_info sgtk_gdk_join_style_info;
extern sgtk_enum_info sgtk_gdk_cursor_type_info;
extern sgtk_enum_info sgtk_gdk_event_type_info;
extern sgtk_enum_info sgtk_gdk_notify_type_info;

### The rest of the file OK.


Having Makefile.am looking like this works on both the uni-cpu and the
dual-cpu box.

foo-glue.c: foo.defs
 build-guile-gtk glue $< >$@

main.c: foo.defs
 build-guile-gtk main $< >$@


I can't say that I really understand what the line "$< tmp && mv tmp $@"
does. Doesn't the line "$< >$@" work very much the same? Perhaps someone
can explain what can happen on parallell builds?


Bo