sdbm.c

一套很值得分析的短信SMS开发源代码。是我今年早些时候从taobao上买来的。但我现在也没看完（先说清楚

    (void) apr_sdbm_unlock(db);    

    return status;
}

/*
 * makroom - make room by splitting the overfull page
 * this routine will attempt to make room for SPLTMAX times before
 * giving up.
 */
static apr_status_t makroom(apr_sdbm_t *db, long hash, int need)
{
    long newp;
    char twin[PBLKSIZ];
    char *pag = db->pagbuf;
    char *new = twin;
    register int smax = SPLTMAX;
    apr_status_t status;

    do {
        /*
         * split the current page
         */
        (void) splpage(pag, new, db->hmask + 1);
        /*
         * address of the new page
         */
        newp = (hash & db->hmask) | (db->hmask + 1);

        /*
         * write delay, read avoidence/cache shuffle:
         * select the page for incoming pair: if key is to go to the new page,
         * write out the previous one, and copy the new one over, thus making
         * it the current page. If not, simply write the new page, and we are
         * still looking at the page of interest. current page is not updated
         * here, as sdbm_store will do so, after it inserts the incoming pair.
         */
        if (hash & (db->hmask + 1)) {
            if ((status = write_page(db, db->pagbuf, db->pagbno)) 
                        != APR_SUCCESS)
                return status;
                    
            db->pagbno = newp;
            (void) memcpy(pag, new, PBLKSIZ);
        }
        else {
            if ((status = write_page(db, new, newp)) != APR_SUCCESS)
                return status;
        }

        if ((status = setdbit(db, db->curbit)) != APR_SUCCESS)
            return status;
        /*
         * see if we have enough room now
         */
        if (fitpair(pag, need))
            return APR_SUCCESS;
        /*
         * try again... update curbit and hmask as getpage would have
         * done. because of our update of the current page, we do not
         * need to read in anything. BUT we have to write the current
         * [deferred] page out, as the window of failure is too great.
         */
        db->curbit = 2 * db->curbit
                   + ((hash & (db->hmask + 1)) ? 2 : 1);
        db->hmask |= db->hmask + 1;
            
        if ((status = write_page(db, db->pagbuf, db->pagbno))
                    != APR_SUCCESS)
            return status;
            
    } while (--smax);

    /*
     * if we are here, this is real bad news. After SPLTMAX splits,
     * we still cannot fit the key. say goodnight.
     */
#if 0
    (void) write(2, "sdbm: cannot insert after SPLTMAX attempts.\n", 44);
#endif
    /* ### ENOSPC not really appropriate but better than nothing */
    return APR_ENOSPC;

}

/* Reads 'len' bytes from file 'f' at offset 'off' into buf.
 * 'off' is given relative to the start of the file.
 * If EOF is returned while reading, this is taken as success.
 */
static apr_status_t read_from(apr_file_t *f, void *buf, 
             apr_off_t off, apr_size_t len)
{
    apr_status_t status;

    if ((status = apr_file_seek(f, APR_SET, &off)) != APR_SUCCESS ||
        ((status = apr_file_read_full(f, buf, len, NULL)) != APR_SUCCESS)) {
        /* if EOF is reached, pretend we read all zero's */
        if (status == APR_EOF) {
            memset(buf, 0, len);
            status = APR_SUCCESS;
        }
    }

    return status;
}

/*
 * the following two routines will break if
 * deletions aren't taken into account. (ndbm bug)
 */
APU_DECLARE(apr_status_t) apr_sdbm_firstkey(apr_sdbm_t *db, 
                                            apr_sdbm_datum_t *key)
{
    apr_status_t status;
    
    if ((status = apr_sdbm_lock(db, APR_FLOCK_SHARED)) != APR_SUCCESS)
        return status;

    /*
     * start at page 0
     */
    if ((status = read_from(db->pagf, db->pagbuf, OFF_PAG(0), PBLKSIZ))
                == APR_SUCCESS) {
        db->pagbno = 0;
        db->blkptr = 0;
        db->keyptr = 0;
        status = getnext(key, db);
    }

    (void) apr_sdbm_unlock(db);

    return status;
}

APU_DECLARE(apr_status_t) apr_sdbm_nextkey(apr_sdbm_t *db, 
                                           apr_sdbm_datum_t *key)
{
    apr_status_t status;
    
    if ((status = apr_sdbm_lock(db, APR_FLOCK_SHARED)) != APR_SUCCESS)
        return status;

    status = getnext(key, db);

    (void) apr_sdbm_unlock(db);

    return status;
}

/*
 * all important binary tree traversal
 */
static apr_status_t getpage(apr_sdbm_t *db, long hash)
{
    register int hbit;
    register long dbit;
    register long pagb;
    apr_status_t status;

    dbit = 0;
    hbit = 0;
    while (dbit < db->maxbno && getdbit(db, dbit))
    dbit = 2 * dbit + ((hash & (1 << hbit++)) ? 2 : 1);

    debug(("dbit: %d...", dbit));

    db->curbit = dbit;
    db->hmask = masks[hbit];

    pagb = hash & db->hmask;
    /*
     * see if the block we need is already in memory.
     * note: this lookaside cache has about 10% hit rate.
     */
    if (pagb != db->pagbno) { 
        /*
         * note: here, we assume a "hole" is read as 0s.
         * if not, must zero pagbuf first.
         * ### joe: this assumption was surely never correct? but
         * ### we make it so in read_from anyway.
         */
        if ((status = read_from(db->pagf, db->pagbuf, OFF_PAG(pagb), PBLKSIZ)) 
                    != APR_SUCCESS)
            return status;

        if (!chkpage(db->pagbuf))
            return APR_ENOSPC; /* ### better error? */
        db->pagbno = pagb;

        debug(("pag read: %d\n", pagb));
    }
    return APR_SUCCESS;
}

static int getdbit(apr_sdbm_t *db, long dbit)
{
    register long c;
    register long dirb;

    c = dbit / BYTESIZ;
    dirb = c / DBLKSIZ;

    if (dirb != db->dirbno) {
        if (read_from(db->dirf, db->dirbuf, OFF_DIR(dirb), DBLKSIZ)
                    != APR_SUCCESS)
            return 0;

        db->dirbno = dirb;

        debug(("dir read: %d\n", dirb));
    }

    return db->dirbuf[c % DBLKSIZ] & (1 << dbit % BYTESIZ);
}

static apr_status_t setdbit(apr_sdbm_t *db, long dbit)
{
    register long c;
    register long dirb;
    apr_status_t status;
    apr_off_t off;

    c = dbit / BYTESIZ;
    dirb = c / DBLKSIZ;

    if (dirb != db->dirbno) {
        if ((status = read_from(db->dirf, db->dirbuf, OFF_DIR(dirb), DBLKSIZ))
                    != APR_SUCCESS)
            return status;

        db->dirbno = dirb;
        
        debug(("dir read: %d\n", dirb));
    }

    db->dirbuf[c % DBLKSIZ] |= (1 << dbit % BYTESIZ);

    if (dbit >= db->maxbno)
        db->maxbno += DBLKSIZ * BYTESIZ;

    off = OFF_DIR(dirb);
    if ((status = apr_file_seek(db->dirf, APR_SET, &off)) == APR_SUCCESS)
        status = apr_file_write_full(db->dirf, db->dirbuf, DBLKSIZ, NULL);

    return status;
}

/*
* getnext - get the next key in the page, and if done with
* the page, try the next page in sequence
*/
static apr_status_t getnext(apr_sdbm_datum_t *key, apr_sdbm_t *db)
{
    apr_status_t status;
    for (;;) {
        db->keyptr++;
        *key = getnkey(db->pagbuf, db->keyptr);
        if (key->dptr != NULL)
            return APR_SUCCESS;
        /*
         * we either run out, or there is nothing on this page..
         * try the next one... If we lost our position on the
         * file, we will have to seek.
         */
        db->keyptr = 0;
        if (db->pagbno != db->blkptr++) {
            apr_off_t off = OFF_PAG(db->blkptr);
            if ((status = apr_file_seek(db->pagf, APR_SET, &off) 
                        != APR_SUCCESS))
                return status;
        }

        db->pagbno = db->blkptr;
        /* ### EOF acceptable here too? */
        if ((status = apr_file_read_full(db->pagf, db->pagbuf, PBLKSIZ, NULL))
                    != APR_SUCCESS)
            return status;
        if (!chkpage(db->pagbuf))
            return APR_EGENERAL;     /* ### need better error */
    }

    /* NOTREACHED */
}


APU_DECLARE(int) apr_sdbm_rdonly(apr_sdbm_t *db)
{
    /* ### Should we return true if the first lock is a share lock,
     *     to reflect that apr_sdbm_store and apr_sdbm_delete will fail?
     */
    return (db->flags & SDBM_RDONLY) != 0;
}