Parallel Execution
GNU `make' knows how to execute several commands at once. Normally,
`make' will execute only one command at a time, waiting for it to
finish before executing the next. However, the `-j' or `--jobs' option
tells `make' to execute many commands simultaneously.
Well, without examples in the manual, we are left to guess and
experiment. For instance, I have discovered that one will not see
parallelism with make -j a, but will with make -j b:
a:
sleep 11
sleep 12
b: c d
c:
sleep 7
d:
sleep 5
So this, say, could be documented.
Maybe mention that this shows equivalence with sleep tests:
$ f=$SECONDS;make -j x y;expr $SECONDS - $f
$ f=$SECONDS;make x& make y& wait;expr $SECONDS - $f
But wait, that is only if x and y don't have any dependencies.
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