GNU make's -j option

Question

Ever since I learned about -j I\'ve used -j8 blithely. The other day I was compiling an atlas installation and the make failed. Eventually I tracked it down to things being ma

Answer 1

It is a good idea to have an automated test to test the -j option of ALL the make files. Even the best developers have problems with the -j option of make. The most common issues is the simplest.

myrule: subrule1 subrule2
     echo done

subrule1:
     echo hello

subrule2:
     echo world

In normal make, you will see hello -> world -> done. With make -j 4, you will might see world -> hello -> done

Where I have see this happen most is with the creation of output directories. For example:

build: $(DIRS) $(OBJECTS)
     echo done

$(DIRS):
     -@mkdir -p $@

$(OBJECTS):
     $(CC) ...