On 14/06/2018 20:34, Howard Chu wrote:

Hallvard Breien Furuseth wrote:

...

Wait, what?  The child didn't write any pids to the table.  If there are pids for it to clear, something is wrong. That can be:

No, there most likely aren't PIDs for it to clear. But most importantly, it must not clear using env->me_pid since that is still the parent's PID.

...

• The pid is from an older run, and the system reused the pid.  If we

code for this, it should be to clear such pids during mdb_env_open.    It gets very arbitrary to clear them when the user does env_close()    in the child and the child happens to have the that reused pid.

No. If the system reused the PID then that means the previous owner of that PID is dead already anyway.

Right...

If there are any table entries under that PID there's no problem removing them.

The problem is that it's arbitrary. Something is exiting without clearing its pid slots, and 0.001% of the time this code will catch it.

Better to skip this cleanup, or to always do it - but "always" belongs in env_open(). If a new env is seeing its pid in use, then it can safely clean it out. Last we talked about that, I liked it and you did not:-)

...

• The child opened a new MDB_env with the same path, and closes the

parent's env afterwards.  Don't Do That, users.  But what to do in    this situation, if we are to have code for it, is to do nothing with    the lockfile.  Not close it either, since closing it will lose the    lock for the env which was opened in the child.

That's a completely different case. This ITS is specifically about a process with an open environment that subsequently forks.

No, I mean:

Parent, pid P: open env A.

Child, pid Q: - open and start using env B with the same path. - close env A, while B is still open. With the new code, this clears pid Q - i.e. B's pids. But lmdb.h already lists that as a "don't do that", because it also removes B's lock on the lockfile.