Closed ale5000-git closed 1 day ago
You've now reached the point where the abstractions break down and the implementation details start to leak out.
This has been discussed previously in issue #375.
It sometimes happens that $!
isn't the pid of the process you actually wanted to run. Instead it's the pid of an intermediate process.
If you run my_func_timeout
directly everything is fine and $!
reports the pid of the background process you wanted to kill.
Running it as a command substitution is more complex. If I add a call to ps
in the script here's what I get:
~ $ output=$(my_func_timeout)
[1] 2588
PID PPID USER TIME ELAPSED COMMAND
0 0 root 0:00 53:11 [System Process]
4 0 root 0:00 53:11 System
...
2940 2224 rmy 0:00 0:41 sh -l
2680 2940 rmy 0:00 0:41 conhost.exe
3168 2940 rmy 0:00 0:00 sh --fs 00000184
2588 3168 rmy 0:00 0:00 sh --fs 00000164
1236 3168 rmy 0:00 0:00 ps
2876 2588 rmy 0:00 0:00 sleep 120
Killing... 2588
$
The pid reported by $!
(2588) is an intermediate shell, an implementation detail. The sleep
is a child of that process. Passing 2588 to kill
signals the intermediate shell, not the sleep
.
I'd also modified the script so it passed the negative of the pid to kill
:
kill -9 "-${_pid}" 1>&2 || echo 1>&2 "${?}"
On Linux using a negative pid signals a process group. In busybox-w32 it approximates this by signalling the given pid and all its children. In the example above the effect of this was to kill process 2588 and its child, 2876, the sleep
. Which is (sort of) what was intended.
Whether this would work for you depends on what you actually want to achieve in your application.
The my_func
run cut
(some implementations may freeze forever), so I have to terminate it after some time.
The example with sleep and a negative pid seems to work on busybox-w32 but on bash online it say:
main.bash: line 15: kill: (-11684) - No such process
Do you know why it say this?
I don't know. My guess would be that the background process isn't a process group leader. (Though I must confess my knowledge of such things is minimal.)
Thanks for the reply. I guess there is not much that can be done, so I'm closing this.
PS: If there is someone that have an idea feel free to post even if it is closed.
Sample code:
I expected to see "End" after 1 second, but it doesn't work.