On 3/29/2010 2:18 PM, tom honermann wrote:
.INTERMEDIATE: yacc.ts
all: y.tab.h y.tab.c y.output y.tab.o
clean:
rm -f y.tab.h y.tab.c y.output y.tab.o
grammar.y:
@touch $@
yacc.ts: grammar.y
@echo "Running yacc..."
@sleep 1
@touch y.tab.h y.tab.c y.output
y.tab.h y.tab.c y.output: yacc.ts
y.tab.o: y.tab.c y.tab.h
@echo "Compiling y.tab.c..."
@sleep 1
@touch $@
The only problem I could find with this approach is that downstream
targets might not get rebuilt as expected. For example, run gmake
once to build everything, then remove y.output and run gmake again.
Using make 3.81 on Linux, y.output is rebuilt which also rebuilds
y.tab.c and y.tab.h, but y.tab.o is not rebuilt (as might be expected
since y.tab.h and y.tab.c were regenerated). This makes sense because
gmake has no way of knowing that rebuilding y.output would also
regenerate y.tab.h and y.tab.c. A full solution for static multiple
target rules would recognize that these files had been regenerated and
would also rebuild y.tab.o. But, I think this is good enough for my
use cases.
This isn't working as well as I had at first thought. For example,
updating grammar.y doesn't always result in y.tab.o getting rebuilt.
This can be reproduced consistently in parallel make invocations:
rtdc60007stdb:$ gmake clean
rm -f y.tab.h y.tab.c y.output y.tab.o
rtdc60007stdb:$ gmake
Running yacc...
Compiling y.tab.c...
rtdc60007stdb:$ touch grammar.y
rtdc60007stdb:$ gmake
Running yacc...
Compiling y.tab.c...
rtdc60007stdb:$ gmake
gmake: Nothing to be done for `all'.
rtdc60007stdb:$ gmake clean
rm -f y.tab.h y.tab.c y.output y.tab.o
rtdc60007stdb:$ gmake -j
Running yacc...
Compiling y.tab.c...
rtdc60007stdb:$ touch grammar.y
rtdc60007stdb:$ gmake -j
Running yacc...
rtdc60007stdb:$ gmake -j
Compiling y.tab.c...
rtdc60007stdb:$ gmake -j
gmake: Nothing to be done for `all'.
Note that the second run using '-j' required an extra 'gmake' invocation
before everything was up to date. Bummer.
Tom.
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