1I0Berkeley DB: DbMpool::db_register[P

DbMpool::db_register





#include <db_cxx.h>

intDbMpool::db_register(int ftype,= int (*pgin)(db_pgno_t pgno, void *pgaddr, Dbt *pgcookie),? int (*pgout)(db_pgno_t pgno, void *pgaddr, Dbt *pgcookie));





Description



>The DbMpool::db_register method registers page-in and page-out?functions for files of type ftype in the specified pool.

FIf the pgin function is non-NULL, it is called each time a pageHis read into the memory pool from a file of type ftype, or a pageHis created for a file of type ftype (see the DB_MPOOL_CREATE flagRfor the DbMpoolFile::get method).

GIf the pgout function is non-NULL, it is called each time a page*is written to a file of type ftype.

HBoth the pgin and pgout functions are called with the pageEnumber, a pointer to the page being read or written, and any argumentvpgcookie that was specified to the DbMpoolFile::open functionEwhen the file was opened. The pgin and pgout functionsCshould return 0 on success, and an applicable non-zero errnoHvalue on failure, in which case the shared memory pool interface routineP(and, by extension, any Berkeley DB library function) calling it will also fail,"returning that errno value.

>The purpose of the DbMpool::db_register function is to supportBprocessing when pages are entered into, or flushed from, the pool.GA file type must be specified to make it possible for unrelated threadsGor processes, that are sharing a pool, to evict each other's pages from@the pool. Applications should call DbMpool::db_register, duringJinitialization, for each type of file requiring input or output processingHthat will be sharing the underlying pool. (No registry is necessary formthe standard access method types, btree, hash and recno, as Db::openregisters them separately.)

?If a thread or process does not call DbMpool::db_register for aHfile type, it is impossible for it to evict pages for any file requiring;input or output processing from the pool. For this reason,@DbMpool::db_register should always be called by each applicationHsharing a pool for each type of file included in the pool, regardless of>whether or not the application itself uses files of that type.

HThere are no standard values for ftype, pgin, pgoutGand pgcookie, except that the ftype value for a file mustLbe a non-zero positive number, as negative numbers are reserved for internalRuse by the Berkeley DB library. For this reason, applications sharing a pool must+coordinate their values amongst themselves.

The DbMpool::db_register>method either returns errno or throws an exception that:encapsulates an errno on failure, and 0 on success.



Errors

[If a fatal error occurs in Berkeley DB, the DbMpool::db_register method may fail and eitherIreturn DB_RUNRECOVERY or throw an exception encapsulating DB_RUNRECOVERY,Gat which point all subsequent database calls will also fail in the sameFway. Methods marked as returning errno will, by default, throwHan exception that encapsulates the error information. The default error\behavior can be changed, see DbException.

The DbMpool::db_register&method may fail and throw an exceptionKfor any of the errors specified for the following Berkeley DB and C library functions: abort(3), fcntl(3), fprintf(3), getpid(3), malloc(3),and memset(3).



Class

6DbMpool



See Also

>DbMpool::close,<DbMpool::open,DbMpool::db_register,<DbMpool::stat,<DbMpool::sync,ADbMpool::trickleand@DbMpool::unlink.
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