Chapter 13.  The DbTxn Handle

#include <db_cxx.h>

class DbTxn {
    DB_TXN *DbTxn::get_DB_TXN();
    const DB_TXN *DbTxn::get_const_DB_TXN() const;
    static DbTxn *DbTxn::get_DbTxn(DB_TXN *txn);
    static const DbTxn *DbTxn::get_const_DbTxn(const DB_TXN *txn);


The DbTxn object is the handle for a transaction. Methods of the DbTxn handle are used to configure, abort and commit the transaction. DbTxn handles are provided to Db methods in order to transactionally protect those database operations.

DbTxn handles are not free-threaded; transactions handles may be used by multiple threads, but only serially, that is, the application must serialize access to the DbTxn handle. Once the DbTxn::abort() or DbTxn::commit() methods are called, the handle may not be accessed again, regardless of the method's return. In addition, parent transactions may not issue any Berkeley DB operations while they have active child transactions (child transactions that have not yet been committed or aborted) except for DbEnv::txn_begin(), DbTxn::abort() and DbTxn::commit().

Each DbTxn object has an associated DB_TXN struct, which is used by the underlying implementation of Berkeley DB and its C++ language API. The DbTxn::get_DB_TXN() method returns a pointer to this struct. Given a const DbTxn object, txnMget_const_DB_TXN() returns a const pointer to the same struct.

Given a DB_TXN struct, the DbTxn::get_DbTxn() method returns the corresponding DbTxn object, if there is one. If the DB_TXN object was not associated with a DbTxn (that is, it was not returned from a call to DbTxn::get_DB_TXN()), then the result of DbTxn::get_DbTxn is undefined. Given a const DB_TXN struct, DbTxn::get_const_DbTxn() returns the associated const DbTxn object, if there is one.

These methods may be useful for Berkeley DB applications including both C and C++ language software. It should not be necessary to use these calls in a purely C++ application.

Transaction Subsystem and Related Methods