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

Just thought I would add to subsetbrew's answer as it does not show the effect clearly. However adding some sleep commands does. Well it works on linux.

Then running make shows differences with:

• make
• make -j4

---

all: toprule1

toprule1: botrule2 subrule1 subrule2
    @echo toprule 1 start
    @sleep 0.01
    @echo toprule 1 done

subrule1: botrule1
    @echo subrule 1 start
    @sleep 0.08
    @echo subrule 1 done

subrule2: botrule1
    @echo subrule 2 start
    @sleep 0.05
    @echo subrule 2 done

botrule1:
    @echo botrule 1 start
    @sleep 0.20
    @echo "botrule 1 done (good prerequiste in sub)"

botrule2:
    @echo "botrule 2 start"
    @sleep 0.30
    @echo "botrule 2 done (bad prerequiste in top)"