int DB->fd(DB *db, int *fdp);
The DB->fd method copies a file descriptor representative of the underlying database into the memory to which fdp refers. A file descriptor referring to the same file will be returned to all processes that call DB->open with the same file argument. This file descriptor may be safely used as an argument to the fcntl(2) and flock(2) locking functions. The file descriptor is not necessarily associated with any of the underlying files actually used by the access method.
The DB->fd method only supports a coarse-grained form of locking. Applications should use the lock manager where possible.
The DB->fd method returns a non-zero error value on failure and 0 on success.
The DB->fd method may fail and return a non-zero error for errors specified for other Berkeley DB and C library or system functions. If a catastrophic error has occurred, the DB->fd method may fail and return DB_RUNRECOVERY, in which case all subsequent Berkeley DB calls will fail in the same way.
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