## root/libdb/mpool.h

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## INCLUDED FROM

    /*-
     * Copyright (c) 1991, 1993, 1994
     *      The Regents of the University of California.  All rights reserved.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     *      @(#)mpool.h     8.2 (Berkeley) 7/14/94
     */

    #include "queue.h"

    /*
     * The memory pool scheme is a simple one.  Each in-memory page is referenced
     * by a bucket which is threaded in up to two of three ways.  All active pages
     * are threaded on a hash chain (hashed by page number) and an lru chain.
     * Inactive pages are threaded on a free chain.  Each reference to a memory
     * pool is handed an opaque MPOOL cookie which stores all of this information.
     */
    #define HASHSIZE        128
    #define HASHKEY(pgno)   ((pgno - 1) % HASHSIZE)

    /* The BKT structures are the elements of the queues. */
    typedef struct _bkt {
            CIRCLEQ_ENTRY(_bkt) hq;         /* hash queue */
            CIRCLEQ_ENTRY(_bkt) q;          /* lru queue */
            void    *page;                  /* page */
            pgno_t   pgno;                  /* page number */

    #define MPOOL_DIRTY     0x01            /* page needs to be written */
    #define MPOOL_PINNED    0x02            /* page is pinned into memory */
            u_int8_t flags;                 /* flags */
    } BKT;

    typedef struct MPOOL {
            CIRCLEQ_HEAD(_lqh, _bkt) lqh;   /* lru queue head */
                                            /* hash queue array */
            CIRCLEQ_HEAD(_hqh, _bkt) hqh[HASHSIZE];
            pgno_t  curcache;               /* current number of cached pages */
            pgno_t  maxcache;               /* max number of cached pages */
            pgno_t  npages;                 /* number of pages in the file */
            u_long  pagesize;               /* file page size */
            int     fd;                     /* file descriptor */
                                            /* page in conversion routine */
            void    (*pgin)(void *, pgno_t, void *);
                                            /* page out conversion routine */
            void    (*pgout)(void *, pgno_t, void *);
            void    *pgcookie;              /* cookie for page in/out routines */
    #ifdef STATISTICS
            u_long  cachehit;
            u_long  cachemiss;
            u_long  pagealloc;
            u_long  pageflush;
            u_long  pageget;
            u_long  pagenew;
            u_long  pageput;
            u_long  pageread;
            u_long  pagewrite;
    #endif
    } MPOOL;

    MPOOL   *mpool_open(void *, int, pgno_t, pgno_t);
    void     mpool_filter(MPOOL *, void (*)(void *, pgno_t, void *),
                void (*)(void *, pgno_t, void *), void *);
    void    *mpool_new(MPOOL *, pgno_t *);
    void    *mpool_get(MPOOL *, pgno_t, u_int);
    int      mpool_put(MPOOL *, void *, u_int);
    int      mpool_sync(MPOOL *);
    int      mpool_close(MPOOL *);
    #ifdef STATISTICS
    void     mpool_stat(MPOOL *);
    #endif

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