Re: Static multiple target rules

[tom honermann]

On 3/30/2010 2:14 AM, Edward Welbourne wrote:
> > >    y.tab.h y.tab.c y.output: yacc.ts
> > >       
> I don't actually see that y.output serves any role in this; simply
> remove every reference to it and your example should be clearer.
>   
It actually does serve a roll for testing purposes.  Try the following 
with this test case:

   gmake clean
   gmake
   rm y.output
   gmake
   gmake

With GNU make 3.81, the second to last gmake invocation rebuilds 
y.output which also
rebuilds y.tab.h and y.tab.c, but y.tab.o (now out of date) doesn't get 
rebuilt.  An additional
gmake invocation is necessary to get everything up to date - which is 
not desirable behavior.
> > >    y.tab.o: y.tab.c y.tab.h
> > >       
> I don't understand .INTERMEDIATE well enough to know why this chain
> fails to lead to y.tab.o's rule being run after yacc.ts's rule has
> been run, in your -j case.  Something strange is going on,
>   
I think what is happening is that time stamps are being checked "too 
early" in some cases.
Make can't infer that y.tab.h, y.tab.c, and y.output are updated by the 
commands for
yacc.ts.  Depending on when it checks the time stamps for those files, 
it may see the
times before or after the commands for yacc.ts are run.  I recall seeing 
emails regarding
GNU make caching time stamps, so that could contribute to this.  
Parallel builds would
behave differently since a shared cache isn't used and each process 
would have to
check time stamps on its own.  So, behavior varies.