Why does my Berkeley DB concurrent data store application hang?

My application hangs when trying to open a concurrent data store (CDB) database for reading:

#0  0x0000003ad860b309 in pthread_cond_wait@@GLIBC_2.3.2 ()
   from /lib64/libpthread.so.0
#1  0x00007ffff7ce67de in __db_pthread_mutex_lock (env=0x610960, mutex=100)
    at /home/steve/ldm/package/src/Berkeley-DB/dist/../mutex/mut_pthread.c:318
#2  0x00007ffff7ce5ea5 in __db_tas_mutex_lock_int (env=0x610960, mutex=100, 
    nowait=0)
    at /home/steve/ldm/package/src/Berkeley-DB/dist/../mutex/mut_tas.c:218
#3  0x00007ffff7ce5c43 in __db_tas_mutex_lock (env=0x610960, mutex=100)
    at /home/steve/ldm/package/src/Berkeley-DB/dist/../mutex/mut_tas.c:248
#4  0x00007ffff7d3715b in __lock_id (env=0x610960, idp=0x0, lkp=0x610e88)
    at /home/steve/ldm/package/src/Berkeley-DB/dist/../lock/lock_id.c:68
#5  0x00007ffff7da1b4d in __fop_file_setup (dbp=0x610df0, ip=0x0, txn=0x0, 
    name=0x40b050 "registry.db", mode=0, flags=1024, retidp=0x7fffffffdd94)
    at /home/steve/ldm/package/src/Berkeley-DB/dist/../fileops/fop_util.c:243
#6  0x00007ffff7d70c8e in __db_open (dbp=0x610df0, ip=0x0, txn=0x0, 
    fname=0x40b050 "registry.db", dname=0x0, type=DB_BTREE, flags=1024, 
    mode=0, meta_pgno=0)
    at /home/steve/ldm/package/src/Berkeley-DB/dist/../db/db_open.c:176
#7  0x00007ffff7d673b2 in __db_open_pp (dbp=0x610df0, txn=0x0, 
    fname=0x40b050 "registry.db", dname=0x0, type=DB_BTREE, flags=1024, mode=0)
    at /home/steve/ldm/package/src/Berkeley-DB/dist/../db/db_iface.c:1146

I suspect that the database environment believes that another process has the database open for writing. This cannot be the case, however, as all applications that access the database do so via an interface library I wrote that registers a termination function via the atexit() system-call to ensure that both the DB and DB_ENV handles 开发者_高级运维are properly closed -- and all previously-executed applications terminated normally.

The interface library opens the database like this:

int status;
Backend*    backend = (Backend*)malloc(sizeof(Backend));

if (NULL == backend) {
    ...
}
else {
    DB_ENV* env;

    if (status = db_env_create(&env, 0)) {
       ...
    }
    else {
        if (status = env->open(env, path,
                DB_CREATE | DB_INIT_CDB | DB_INIT_MPOOL, 0)) {
            ...
        }
        else {
            DB*     db;

            if (status = db_create(&db, env, 0)) {
            ...
            }
            else {
                if (status = db->open(db, NULL, DB_FILENAME, NULL,
                        DB_BTREE, forWriting ? DB_CREATE : DB_RDONLY, 0)) {
                    ...
                }
                else {
                    backend->db = db;
                }                   /* "db" opened */

                if (status)
                    db->close(db, 0);
           }                       /* "db" allocated */

           if (status) {
               env->close(env, 0);
               env = NULL;
           }
        }                       /* "env" opened */

        if (status && NULL != env)
            env->close(env, 0);
    }                               /* "env" allocated */

    if (status)
        free(backend);
}                                   /* "backend" allocated */

This code encounters no errors.

The interface library also registers the following code to be executed when any process that uses the interface library exits:

if (NULL != backend) {
    DB*         db = backend->db;
    DB_ENV*     env = db->get_env(db);

    if (db->close(db, 0)) {
        ...
    }
    else {
        if (env->close(env, 0)) {
            ...
        }
        else {
            /* database properly closed */
        }
    }
}

As I indicated, all previously-executed processes that use the interface library terminated normally. All such processes are single-threaded.

I'm using version 4.8.24.NC of Berkeley DB on the following platform:

$ uname -a
Linux gilda.unidata.ucar.edu 2.6.27.41-170.2.117.fc10.x86_64 #1 SMP Thu Dec 10 10:36:29 EST 2009 x86_64 x86_64 x86_64 GNU/Linux

Any ideas?

Apologies that this question went unanswered for so long. In the future you might want to post your question to the Berkeley DB Forum on the Oracle Technology Network here. This is a very active forum where Support, Engineering and BDB application developers interact directly.

Your description of the problem validates your assumption that the BDB environment may think that the table is already open for write access. You can use db_stat to look at the environment statistics. This is likely an application problem, but one of the BDB engineers could probably help you isolate the problem on the BDB forum listed above.