CODEWITHSUNDEEP
parallel-processingmakefilegnu-make
Jens
Jens

Reputation: 72639

parallel GNU make and rules that create several targets at once

I have in my GNU makefile (among others) several rules of the form

a b c d: x
        program $^

i.e. program creates the files a, b, c and d with just one invokation. When I run this with gmake -j 4, make spawns four program runs in parallel, because none of the files exist and none has a dependency on the other.

I can fix this by providing a "fake dependency chain" (for lack of a better term):

a: x
        program $^
b: a
c: b
d: c

Is there a more elegant way to teach gmake to run program only once, even in a parallel build?

EDIT: Any solution should obey the dependency on x and do nothing if a - d are up to date with respect to x.

Upvotes: 0

Views: 541

Answers (1)

MadScientist
MadScientist

Reputation: 100836

If your targets all share a common stem, then you can use pattern rules:

%.a %.b %.c %.d:
        touch $*.a $*.b $*.c $*.d

If they don't then the only thing you can do is create a sentinel file:

a b c d: .sentinel ;
.sentinel: ; touch a b c d $@

Upvotes: 1

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