Concurrent Library Update

Another potential concurrency problem is the default rule for creating libraries that also modifies a fixed file, that is, the library. The inappropriate .c.a rule causes dmake to build each object file and then archive that object file. When dmake archives two object files in parallel, the concurrent updates will corrupt the archive file.

.c.a:
    $(COMPILE.c) -o $% $<
    $(AR) $(ARFLAGS) $@ $%
    $(RM) $%

A better method is to build each object file and then archive all the object files after completion of the builds. An appropriate suffix rule and the corresponding library rule are:

.c.a:
    $(COMPILE.c) -o $% $<

lib.a: lib.a($(OBJECTS))
    $(AR) $(ARFLAGS) $(OBJECTS)
    $(RM) $(OBJECTS)