Berkeley DB: DbMpoolFile::get
Полезная информация


#include <db_cxx.h>

int DbMpoolFile::get(db_pgno_t *pgnoaddr, u_int32_t flags, void **pagep);


The DbMpoolFile::get method copies a pointer to the page with the page number specified by pgnoaddr, from the source file in the DbMpoolFile, into the memory location referenced by pagep. If the page does not exist or cannot be retrieved, DbMpoolFile::get will fail.

Page numbers begin at 0, i.e., the first page in the file is page number 0, not page number 1.

The returned page is size_t type aligned.

The flags argument is specified by logically OR'ing together one or more of the following values:

If the specified page does not exist, create it. In this case, the pgin method, if specified, is called.

Return the last page of the source file and copy its page number to the location referenced by pgnoaddr.

Create a new page in the file and copy its page number to the location referenced by pgnoaddr. In this case, the pgin method, if specified, is not called.

The DB_MPOOL_CREATE, DB_MPOOL_LAST and DB_MPOOL_NEW flags are mutually exclusive.

Created pages have all their bytes set to 0, unless otherwise specified when the file was opened.

All pages returned by DbMpoolFile::get will be retained (i.e. pinned in the pool until a subsequent call to DbMpoolFile::put.

The DbMpoolFile::get method either returns errno or throws an exception that encapsulates an errno on failure, and 0 on success.


If a fatal error occurs in Berkeley DB, the DbMpoolFile::get method may fail and either return DB_RUNRECOVERY or throw an exception encapsulating DB_RUNRECOVERY, at which point all subsequent database calls will also fail in the same way. Methods marked as returning errno will, by default, throw an exception that encapsulates the error information. The default error behavior can be changed, see DbException.

The DbMpoolFile::get method may fail and throw an exception for any of the errors specified for the following Berkeley DB and C library functions: DBmemp->pgin(3), DBmemp->pgout(3), abort(3), close(3), dbenv->db_paniccall(3), fcntl(3), fflush(3), fprintf(3), free(3), fstat(3), fsync(3), getenv(3), getpid(3), getuid(3), isdigit(3), DbLog::compare, DbLog::flush, lseek(3), malloc(3), memcmp(3), memcpy(3), memset(3), mmap(3), open(3), pread(3), pstat_getdynamic(3), pwrite(3), read(3), sigfillset(3), sigprocmask(3), stat(3), strerror(3), strlen(3), sysconf(3), time(3), unlink(3), vfprintf(3), vsnprintf(3), and write(3).

In addition, the DbMpoolFile::get method may fail and throw an exception or return errno for the following conditions:

The page reference count has overflowed. (This should never happen unless there's a bug in the application.)

An invalid flag value or parameter was specified.

The DB_MPOOL_NEW flag was set and the source file was not opened for writing.

The requested page does not exist and DB_MPOOL_CREATE was not set.

More than one of DB_MPOOL_CREATE, DB_MPOOL_LAST and DB_MPOOL_NEW was set.

The cache is full and no more pages will fit in the pool.



See Also

DbMpoolFile::close, DbMpoolFile::get, DbMpoolFile::open, DbMpoolFile::put, DbMpoolFile::set and DbMpoolFile::sync.