churchyard / rpms / python3

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diff -up Python-3.2a1/Makefile.pre.in.parallel-grammar Python-3.2a1/Makefile.pre.in
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--- Python-3.2a1/Makefile.pre.in.parallel-grammar	2010-08-20 15:09:13.613527156 -0400
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+++ Python-3.2a1/Makefile.pre.in	2010-08-20 15:10:31.428135355 -0400
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@@ -222,6 +222,7 @@ IO_OBJS=	\
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 ##########################################################################
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 # Grammar
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+GRAMMAR_STAMP=	$(srcdir)/grammar-stamp
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 GRAMMAR_H=	$(srcdir)/Include/graminit.h
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 GRAMMAR_C=	$(srcdir)/Python/graminit.c
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 GRAMMAR_INPUT=	$(srcdir)/Grammar/Grammar
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@@ -557,9 +558,24 @@ Modules/python.o: $(srcdir)/Modules/pyth
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 $(IO_OBJS): $(IO_H)
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-$(GRAMMAR_H) $(GRAMMAR_C): $(PGEN) $(GRAMMAR_INPUT)
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+# GNU "make" interprets rules with two dependents as two copies of the rule.
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+#
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+# In a parallel build this can lead to pgen being run twice, once for each of
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+# GRAMMAR_H and GRAMMAR_C, leading to race conditions in which the compiler
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+# reads a partially-overwritten copy of one of these files, leading to syntax
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+# errors (or linker errors if the fragment happens to be syntactically valid C)
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+#
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+# See http://www.gnu.org/software/hello/manual/automake/Multiple-Outputs.html
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+# for more information
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+#
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+# Introduce ".grammar-stamp" as a contrived single output from PGEN to avoid
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+# this:
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+$(GRAMMAR_H) $(GRAMMAR_C): $(GRAMMAR_STAMP)
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+
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+$(GRAMMAR_STAMP): $(PGEN) $(GRAMMAR_INPUT)
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 		-@$(INSTALL) -d Include
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 		-$(PGEN) $(GRAMMAR_INPUT) $(GRAMMAR_H) $(GRAMMAR_C)
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+		touch $(GRAMMAR_STAMP)
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 $(PGEN):	$(PGENOBJS)
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 		$(CC) $(OPT) $(PY_LDFLAGS) $(PGENOBJS) $(LIBS) -o $(PGEN)