#include <db_cxx.h> int DbEnv::failchk(u_int32_t flags);
The DbEnv::failchk() method checks for threads of control (either a
true thread or a process) that have exited while manipulating Berkeley
DB library data structures, while holding a logical database lock, or
with an unresolved transaction (that is, a transaction that was never
aborted or committed). For more information, see
Architecting Data Store and
Concurrent Data Store applications, and
Architecting Transactional
Data Store applications, both in the
Berkeley DB Programmer's Reference Guide.
The DbEnv::failchk() method is
used in conjunction with the
DbEnv::set_thread_count(),
DbEnv::set_isalive() and
DbEnv::set_thread_id()
methods. Before calling the failchk()method, applications must:
Configure their database using the DbEnv::set_thread_count() method.
Establish an is_alive() function and
invoke
DbEnv::set_isalive()
with that function as the is_alive parameter.
Establish a thread_id function and
invoke
DbEnv::set_thread_id()
with that function as the thread_id
parameter.
If any of these methods are omitted, a program may be unable to
allocate a thread control block. This is true of the standalone
Berkeley DB utility programs. To avoid problems when using the
standalone Berkeley DB utility programs with environments
configured for failure checking, incorporate the utility's
functionality directly in the application, or call the
DbEnv::failchk() method along with its
associated methods before running the utility.
If DbEnv::failchk() determines a thread of control exited while
holding database read locks, it will release those locks. If
DbEnv::failchk() determines a thread of control exited with an
unresolved transaction, the transaction will be aborted. In either of
these cases, DbEnv::failchk() will return 0 and the application may
continue to use the database environment.
In either of these cases, the DbEnv::failchk() method will also
report the process and thread IDs associated with any released locks
or aborted transactions. The information is printed to a specified
output channel (see the
DbEnv::set_msgfile()
method for more information), or passed to an application callback
function (see the
DbEnv::set_msgcall()
method for more information).
If DbEnv::failchk() determines a thread of control has exited such
that database environment recovery is required, it will return
DB_RUNRECOVERY.
In this case, the application should not continue to use the database
environment. For a further description as to the actions the
application should take when this failure occurs, see
Handling failure in Data Store and
Concurrent Data Store applications, and
Handling failure in Transactional Data
Store applications, both in the
Berkeley DB Programmer's Reference Guide.
In multiprocess applications, it is recommended that the DbEnv handle
used to invoke the DbEnv::failchk() method not be shared and therefore
not free-threaded.
The DbEnv::failchk() method may not be called by the
application before the DbEnv::open()
method is called.
The DbEnv::failchk()
method either returns a non-zero error value or throws an
exception that encapsulates a non-zero error value on
failure, and returns 0 on success.
The DbEnv::failchk()
method may fail and throw a DbException
exception, encapsulating one of the following non-zero errors, or return one
of the following non-zero errors: