/* PSPP - a program for statistical analysis.
Copyright (C) 2007, 2009, 2010 Free Software Foundation, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see . */
#ifndef DATA_CASEREADER_SHIM_H
#define DATA_CASEREADER_SHIM_H 1
/* Buffering shim for implementing clone and peek operations.
The "clone" and "peek" operations aren't implemented by all types of
casereaders, but we have to expose a uniform interface anyhow. The
casereader buffering shim can do this by interposing a buffer on top of an
existing casereader. The shim maintains a window of cases that spans the
positions of the original casereader and all of its clones (the "clone
set"), from the position of the casereader that has read the fewest cases to
the position of the casereader that has read the most.
Thus, if all of the casereaders in the clone set are at approximately the
same position, only a few cases are buffered and there is little
inefficiency. If, on the other hand, one casereader is not used to read any
cases at all, but another one is used to read all of the cases, the entire
contents of the casereader is copied into the buffer. This still might not
be so inefficient, given that case data in memory is shared across multiple
identical copies, but in the worst case the window implementation will write
cases to disk instead of maintaining them in-memory.
Casereader buffering shims are inserted automatically on the first call to
casereader_clone() or casereader_peek() for a casereader that does not
support those operations natively. Thus, there is ordinarily little reason
to intentionally insert a shim. */
struct casereader;
struct casereader_shim *casereader_shim_insert (struct casereader *);
void casereader_shim_slurp (struct casereader_shim *);
#endif /* data/casereader-shim.h */