Re: Multiple threads and mdb_dbi_open

Thanks, I think I get it now.

On Thu, Sep 11, 2014 at 5:06 PM, Howard Chu hyc@symas.com wrote:

Harry B wrote:

...

Let me rephrase and see if I understand correctly.

1. If I have 10 threads (but only one database), then I would need to

create 10 dbi handles to the same DB and then use them as required from each thread making sure no two threads share the same DBI handle?

No. Re-read the documentation that you linked. It very clearly states that if you open the same DB multiple times you will get the same handle back, so why would you ever try to open it 10 times for 10 threads??

It also says very clearly that after the handle is persisted into the shared environment it may be used by other transactions.

2. Inside each thread, I would open a new transaction (as required for the

...

then relevant/appropriate read/write operation), but I would use a DBI handle obtained in the main thread even though that DBI was created using a different transaction handle that the one we are about to use for the current thread?

Thanks

...

-- Harry

On Thu, Sep 11, 2014 at 4:35 PM, Howard Chu <hyc@symas.com mailto:hyc@symas.com> wrote:

Harry B wrote:

    Hello,

    As per the documentation here
    http://symas.com/mdb/doc/__group__mdb.html#__

gac08cad5b096925642ca359a6d6f0__562a http://symas.com/mdb/doc/group__mdb.html# gac08cad5b096925642ca359a6d6f0562a I see the following,

    "This function must not be called from multiple concurrent

transactions. A transaction that uses this function must finish (either commit or abort) before any other transaction may use this function."

    This seems to imply that after one txn has begun on an

environment, I cannot create another txn or dbi until the first one has finished - that doesn't seem to be right.

    If I have multi-threaded app, what is the expected sequence for
    creation of
    Environment, Transaction, and DBI handles?


Before starting any other threads:
   Create the environment.
   Open a transaction.
   Open all DBI handles the app will need.
   Commit the transaction.

After that use the DBI handles freely among any transactions/threads.

-- -- Howard Chu CTO, Symas Corp. http://www.symas.com Director, Highland Sun http://highlandsun.com/hyc/ Chief Architect, OpenLDAP http://www.openldap.org/project/