https://bugs.openldap.org/show_bug.cgi?id=10518

Issue ID: 10518 Summary: Every write transaction leaks a mutex on Windows Product: LMDB Version: unspecified Hardware: x86_64 OS: Windows Status: UNCONFIRMED Keywords: needs_review Severity: normal Priority: --- Component: liblmdb Assignee: bugs@openldap.org Reporter: bhargavabhat@gmail.com Target Milestone: ---

Created attachment 1152 --> https://bugs.openldap.org/attachment.cgi?id=1152&action=edit Create and use the mutex for the duration of the env

I see that on master3 branch, every write transaction leaks a mutex.

LMDB creates a new mutex on every non-read-only transaction in `mdb_txn_renew0`.

In `mdb_txn_end`, when the write transaction finishes, it sets `mode` to 0 and unlocks it.

``` if (!txn->mt_parent) { env->me_txn = NULL; mode = 0; if (env->me_txns) UNLOCK_MUTEX(env->me_wmutex); } ```

Later, it does this.

``` if (mode & MDB_END_FREE) { if (!F_ISSET(txn->mt_flags, MDB_TXN_RDONLY)) pthread_mutex_destroy(&txn->mt_child_mutex); // never reached free(txn); } ```

So we just don't close the mutex. It's probably not a big deal on non-Windows platforms, but on Windows, the number of handles owned by the process keeps increasing which limits the total number of write transactions we can do in the lifetime of the process.

I didn't really understand why we need to create a mutex on every non-read-only transaction. Can we just tie the lifetime of the mutex to the environment instead of the transaction?

I'm attaching a patch which tries to fix it.