Q: how should a multi-thread program open a db

I have a multi-threading program, a milter actually. Each thread needs to
read values from a db file.

Does each thread need to open the db file itself, or can all the threads
share the same handle to read the data? The db file is opened with the
DB_THREAD flag.



I checked some earlier work of mine and the milter opens the db file just
once at startup, and then all the threads used the same handle. That
appeared to work, but I am wondering now if it was a happy coincidence.

/* note the real code checks for errors */

DB *dbp = (DB*)calloc(1,sizeof(DB));
db_create( &dbp, NULL, 0);

flags=0;
flags |= DB_THREAD;
/* DBTXN comes from a sendmail header */
dbp->open(dbp, DBTXN dbfilename, NULL, DB_HASH, flags , 0444);


That single "dbp" handle is then used by all the threads for the db get's.
Is that a problem? Should each thread create and open the db file itself
(i.e. have it's own handle for the get() ? )

Does each thread need to open the db file itself, or can all the threads
share the same handle to read the data? The db file is opened with the
DB_THREAD flag.

That's what the DB_THREAD flag is for: when that flag is specified,
multiple threads can share a single handle.

Regards,
Michael.

Does each thread need to open the db file itself, or can all the threads
share the same handle to read the data? The db file is opened with the
DB_THREAD flag.

That's what the DB_THREAD flag is for: when that flag is specified,
multiple threads can share a single handle.

Regards,
Michael.

Michael Cahill (mjc (AT) sleepycat (DOT) com) wrote:
: > Does each thread need to open the db file itself, or can all the threads
: > share the same handle to read the data? The db file is opened with the
: > DB_THREAD flag.

: That's what the DB_THREAD flag is for: when that flag is specified,
: multiple threads can share a single handle.

That's what I thought, thanks, I just wanted another opinion to
be sure I wasn't out to lunch.