multiple targets created by one command verses --jobs 2

[dave russo]

I've run into a problem using make's job server capability because of a command that generates several targets in one execution.  The job server runs the command multiple times (concurrently) for each target but, because the command is designed to create all targets at once, the command interferes with itself and the build fails.  Even if I fix the command to not interfere with itself, I don't want it to run more than once.

I understand that by using pattern rules multiple targets can be built by running a rule just once, but I don't see a good way to express this particular command as a pattern rule.

My current makefile fragment looks like:

package.h package.c foo.h bar.h: foo.idl bar.idl package.dsc

    idl package.dsc

This "works" when --jobs is set to 1 because make re-checks dependencies after running rules: the rule is run once if any idl file changes, if one or more generated file is inadvertently deleted, or if one or more the generated files is named on the command line.

This fails when --jobs is set to anything greater than 1 because make sees that foo.h and bar.h are required (by other parts of the build) and concurrently runs the idl command.

I tried converting this to a pattern rule as follows:

%.h %.c foo.h bar.h: foo.idl bar.idl %.dsc

    idl package.dsc

But make fails with the following parser error:

makefile: *** mixed implicit and normal rules.  Stop.

I tried converting to the following:

%.h %.c: foo.idl bar.idl %.dsc

    idl package.dsc

foo.h bar.h: package.h

But this does not cover the case that one of the generated header files is deleted nor does it support naming these files as a goal on the command line.

Is there any other way to tell make to not build specified targets in parallel? It sure would be nice if there was some syntax that would allow one to group targets as being generated from a single rule (other than via pattern rules).

Any help would be appreciated.