makefile - How to express dependence on a shared library when making multithreaded -

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i use shared library.so in order avoid remake executables (which linked against it) when implementation (library.cpp), not interface (library.hpp), has changed, i.e.

obj/library.o:    library.cpp library.hpp lib/library.so:    obj/library.o  program        :    program.cpp library.hpp                 $(cxx) program.cpp -llib -lrary

thus, program not depend on library.cpp or library.so. however, when making scratch (rather remaking because of changes files), library.so must made before program. can ensured setting:

default:    library.so program

but when using make -j broken.

so correct way 1) ensure library.so made before program 2) avoid re-making program if library.cpp has changed?

the solution want order-only prerequisite.

from types of prerequisites section of gnu make manual:

occasionally, however, have situation want impose specific ordering on rules invoked without forcing target updated if 1 of rules executed. in case, want define order-only prerequisites. order-only prerequisites can specified placing pipe symbol (|) in prerequisites list: prerequisites left of pipe symbol normal; prerequisites right order-only:

targets : normal-prerequisites | order-only-prerequisites

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