Conserve /proc/$pid after a process exit

[Yubin Ruan]

Does anyone have ideas how to preserve a /proc/$pid directory after a process
exit? I want to perform some audit on some process A from within
another process B. Process B have the pid of process A but after A
exit, B can no longer retrieve
info from /proc/$pid. I am wondering whether it is possible for B to
have a special "handle" of /proc/$pid so that after A exist B can
still read from it.

In my situation, A know nothing of B so A can send no message to B.

Are there any mechanism for this purpose? Locking that dir?

Thanks,
Yubin