You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
- Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
- 02111-1307, USA. */
+ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ 02110-1301, USA. */
#include <config.h>
#include "casefile.h"
#include "settings.h"
#include "var.h"
-#ifdef HAVE_VALGRIND_VALGRIND_H
-#include <valgrind/valgrind.h>
-#endif
-
#define IO_BUF_SIZE (8192 / sizeof (union value))
-/* A casefile is a sequentially accessible array of immutable
- cases. It may be stored in memory or on disk as workspace
- allows. Cases may be appended to the end of the file. Cases
- may be read sequentially starting from the beginning of the
- file. Once any cases have been read, no more cases may be
- appended. The entire file is discarded at once. */
+/* A casefile represents a sequentially accessible stream of
+ immutable cases.
+
+ If workspace allows, a casefile is maintained in memory. If
+ workspace overflows, then the casefile is pushed to disk. In
+ either case the interface presented to callers is kept the
+ same.
+
+ The life cycle of a casefile consists of up to three phases:
+
+ 1. Writing. The casefile initially contains no cases. In
+ this phase, any number of cases may be appended to the
+ end of a casefile. (Cases are never inserted in the
+ middle or before the beginning of a casefile.)
+
+ Use casefile_append() or casefile_append_xfer() to
+ append a case to a casefile.
+
+ 2. Reading. The casefile may be read sequentially,
+ starting from the beginning, by "casereaders". Any
+ number of casereaders may be created, at any time,
+ during the reading phase. Each casereader has an
+ independent position in the casefile.
+
+ Casereaders may only move forward. They cannot move
+ backward to arbitrary records or seek randomly.
+ Cloning casereaders is possible, but it is not yet
+ implemented.
+
+ Use casefile_get_reader() to create a casereader for
+ use in phase 2. This also transitions from phase 1 to
+ phase 2. Calling casefile_mode_reader() makes the same
+ transition, without creating a casereader.
+
+ Use casereader_read(), casereader_read_xfer(), or
+ casereader_read_xfer_assert() to read a case from a
+ casereader. Use casereader_destroy() to discard a
+ casereader when it is no longer needed.
+
+ 3. Destruction. This phase is optional. The casefile is
+ also read with casereaders in this phase, but the
+ ability to create new casereaders is curtailed.
+
+ In this phase, casereaders could still be cloned (once
+ we eventually implement cloning).
+
+ To transition from phase 1 or 2 to phase 3 and create a
+ casereader, call casefile_get_destructive_reader().
+ The same functions apply to the casereader obtained
+ this way as apply to casereaders obtained in phase 2.
+
+ After casefile_get_destructive_reader() is called, no
+ more casereaders may be created with
+ casefile_get_reader() or
+ casefile_get_destructive_reader(). (If cloning of
+ casereaders were implemented, it would still be
+ possible.)
+
+ The purpose of the limitations applied to casereaders
+ in phase 3 is to allow in-memory casefiles to fully
+ transfer ownership of cases to the casereaders,
+ avoiding the need for extra copies of case data. For
+ relatively static data sets with many variables, I
+ suspect (without evidence) that this may be a big
+ performance boost.
+
+ When a casefile is no longer needed, it may be destroyed with
+ casefile_destroy(). This function will also destroy any
+ remaining casereaders. */
/* In-memory cases are arranged in an array of arrays. The top
level is variable size and the size of each bottom level array
projects / pspp / blobdiff