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Re: mdb_dbi_open and threads
Hallvard Breien Furuseth wrote:
On 22. mai 2017 14:00, Howard Chu wrote:
Muhammed Muneer wrote:
Hallvard wrote
"With threads 1 and 2 coexisting? When thread 2 called mdb_dbi_open(),
thread 1's prospect of using mdb_dbi_open() at all was lost."
Yeah with both coexisting. Thats what I thought.
Sorry, I should have said with _transactions_ #1 and #2 coexisting,
_transaction_ #1's prospect of using mdb_dbi_open() at all was lost.
Transaction #3 in thread #1 can use it if it stared after txn#2 ended.
Anyway, just forget about being clever with DBIs. LMDB does not support
DBI cleverness, that's one of its trade-offs for speed and simplicity.
Exactly.
If you want to use dbi_open in multiple threads then put it in your own
wrapper function, protected by a mutex.
Wait, what? mdb_dbi_open() isn't coded to handle concurrent txns
calling it, regardless of any mutexes the caller has. In particular,
it does not use nor update the environment's numdbs, so the two
transactions could end up creating the same DBI for different DBs.
Yes. This is only safe if you also close the dbi in the same txn that opened
it. Which you are probably doing, if you are opening and closing on the fly.
Naturally you will also have to wrap dbi_close the same way.
If we did support this, txn_commit() of the txn which used dbi_open()
would also need the mutex.
--
-- Howard Chu
CTO, Symas Corp. http://www.symas.com
Director, Highland Sun http://highlandsun.com/hyc/
Chief Architect, OpenLDAP http://www.openldap.org/project/