Broom is a minimalistic init-process that can spawn a single immediate child and reaps the indirect children it has to adopt.
Inspired by the article, driven by the itch to do some Rust.
Let's say we run a docker-container with the following init-command:
sample-children/zombie-producer.sh 20 {10..5} {5..10}
That'll spawn quite a lot of child processes:
1 pts/0 Ss+ 0:00 sleep 20
6 pts/0 S+ 0:00 sleep 10
7 pts/0 S+ 0:00 \_ sleep 9
8 pts/0 S+ 0:00 \_ sleep 8
9 pts/0 S+ 0:00 \_ sleep 7
10 pts/0 S+ 0:00 \_ sleep 6
11 pts/0 S+ 0:00 \_ sleep 5
12 pts/0 S+ 0:00 \_ sleep 5
13 pts/0 S+ 0:00 \_ sleep 6
14 pts/0 S+ 0:00 \_ sleep 7
15 pts/0 S+ 0:00 \_ sleep 8
16 pts/0 S+ 0:00 \_ sleep 9
17 pts/0 S+ 0:00 \_ sleep 10
Some of them will terminate soon. Since their parent didn't wait its children the following picture emerges:
1 pts/0 Ss+ 0:00 sleep 20
6 pts/0 Z+ 0:00 [sleep] <defunct>
7 pts/0 Z+ 0:00 [sleep] <defunct>
8 pts/0 Z+ 0:00 [sleep] <defunct>
9 pts/0 Z+ 0:00 [sleep] <defunct>
10 pts/0 Z+ 0:00 [sleep] <defunct>
11 pts/0 Z+ 0:00 [sleep] <defunct>
12 pts/0 Z+ 0:00 [sleep] <defunct>
13 pts/0 Z+ 0:00 [sleep] <defunct>
14 pts/0 Z+ 0:00 [sleep] <defunct>
15 pts/0 Z+ 0:00 [sleep] <defunct>
16 pts/0 Z+ 0:00 [sleep] <defunct>
17 pts/0 Z+ 0:00 [sleep] <defunct>
... which is not good.
If we supply our program with a parent:
broom sample-children/zombie-producer.sh 20 {10..5} {5..10}
1 pts/0 Ss+ 0:00 target/release/broom sample-children/zombie-producer.sh 20 10 9 8 7 6 5 5 6 7 8 9 10
6 pts/0 S+ 0:00 sleep 20
7 pts/0 S+ 0:00 \_ sleep 10
8 pts/0 S+ 0:00 \_ sleep 9
9 pts/0 S+ 0:00 \_ sleep 8
10 pts/0 S+ 0:00 \_ sleep 7
11 pts/0 S+ 0:00 \_ sleep 6
12 pts/0 S+ 0:00 \_ sleep 5
13 pts/0 S+ 0:00 \_ sleep 5
14 pts/0 S+ 0:00 \_ sleep 6
15 pts/0 S+ 0:00 \_ sleep 7
16 pts/0 S+ 0:00 \_ sleep 8
17 pts/0 S+ 0:00 \_ sleep 9
18 pts/0 S+ 0:00 \_ sleep 10
The terminated children will be reaped in a timely manner:
1 pts/0 Ss+ 0:00 target/release/broom sample-children/zombie-producer.sh 20 10 9 8 7 6 5 5 6 7 8 9 10
6 pts/0 S+ 0:00 sleep 20
7 pts/0 Z+ 0:00 \_ [sleep] <defunct>