On 29 September 2016 at 03:39, Hallvard Breien Furuseth h.b.furuseth@usit.uio.no wrote:

Yes. Your concern seems to reduce to a doc bug and an otherwise- harmless file descriptor leak which it is too late to fix completely. So I ended up thinking of resource leaks in general.

Why is it harmless in your opinion?

It'd be pretty intrusive of a _library_ to forbid the user to fork() at all without exec().

From my point of view, that is what the LMDB doc says. I can't use

LMDB and fork(). We're probably approaching this from different angles though: I want to take something away that is de-facto possible, but was not documented to be that way.

No, I mean a partial env_close to be called _after_ the fork, in the child. A child which does not want FD-leaks must in any case do a close() loop or close the mdb_env_get_fd() descriptor. So maybe we just as well should give him a more thorough "free resources in child" call which cleans up a bit for exec()-less programs as well. (It'll need an argument which says just what is safe to clean up - e.g. it can't do much much if the parent is already multi-threaded.)

Sorry, I misunderstood you here.

If I understand you correctly, LMDB would be safe to use in these scenarios in an ideal world:

1. mdb_env_open(), fork(), exec() (without fd leaks I'd argue) 2. mdb_env_open(), pthread_create(), fork() 3. mdb_env_open(), fork()

As far as I understand you are after 2 and 3, while I want 1. Case 2 seems unlikely, given that forking a multi-threaded program is so hard that is rarely makes sense [1]. Case 3 is simply a matter of reordering the calls.

1: http://thorstenball.com/blog/2014/10/13/why-threads-cant-fork/