[RFC] new syscall to allow notification when arbitrary pids die

[Chris Friesen]

I would like to get some comments on a new syscall that I am planning on 
implementing.  This syscall would allow a process to register to be notified 
when another process dies.  The calling process would specify the pid of the 
process in which it is interested and the signal which it wants to be sent when 
the process with the specified pid dies.  The api would be:

int sigexit(pid_t pid, int signum)

The implementation would add a new linked list to the task struct which would 
store pid/signal tuples for each process requesting notification.  On process 
death, in do_notify_parent we walk the list and send the specified signals to 
all the listeners.

I see two immediate uses for this.  One would be to enable a "watcher" process 
which can do useful things on the death of processes which registered with it 
(logging, respawning, notifying other processes, etc).  The watcher could keep a 
persistant list of what its monitoring and what for in a file, and if it ever 
died, the new watcher could scan the list and register to watch them all again. 
The second would be to enable mutual suicide pacts between processes. (I'm not 
sure when I would use this, but it sounds kind of fun.)

Anyone have any opinions on this?  There is a comment in exit_notify about not 
sending signals to arbitrary processes using the thread signals, but I'm not 
sure if that objection was to the idea or to the implementation.

Thanks,

Chris

-- 
Chris Friesen                    | MailStop: 043/33/F10
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