MirOS Manual: mpool(3), mpool_close(3), mpool_delete(3), mpool_filter(3), mpool_get(3), mpool_new(3), mpool_open(3), mpool_put(3), mpool_sync(3)

MPOOL(3)                   BSD Programmer's Manual                    MPOOL(3)

NAME

     mpool_open, mpool_filter, mpool_new, mpool_delete, mpool_get, mpool_put,
     mpool_sync, mpool_close - shared memory buffer pool

SYNOPSIS

     #include <db.h>
     #include <mpool.h>

     MPOOL *
     mpool_open(void *key, int fd, pgno_t pagesize, pgno_t maxcache);

     void
     mpool_filter(MPOOL *mp, void (*pgin)(void *, pgno_t, void *),
             void (*pgout)(void *, pgno_t, void *), void *pgcookie);

     void *
     mpool_new(MPOOL *mp, pgno_t *pgnoaddr, unsigned int flags);

     int
     mpool_delete(MPOOL *mp, void *page);

     void *
     mpool_get(MPOOL *mp, pgno_t pgno, unsigned int flags);

     int
     mpool_put(MPOOL *mp, void *pgaddr, unsigned int flags);

     int
     mpool_sync(MPOOL *mp);

     int
     mpool_close(MPOOL *mp);

DESCRIPTION

     mpool is the library interface intended to provide page-oriented buffer
     management of files. The buffers may be shared between processes.

     The function mpool_open() initializes a memory pool. The key argument is
     the byte string used to negotiate between multiple processes wishing to
     share buffers. If the file buffers are mapped in shared memory, all
     processes using the same key will share the buffers. If key is NULL, the
     buffers are mapped into private memory. The fd argument is a file
     descriptor for the underlying file, which must be seekable. If key is
     non-NULL and matches a file already being mapped, the fd argument is ig-
     nored.

     The pagesize argument is the size, in bytes, of the pages into which the
     file is broken up. The maxcache argument is the maximum number of pages
     from the underlying file to cache at any one time. This value is not re-
     lative to the number of processes which share a file's buffers, but will
     be the largest value specified by any of the processes sharing the file.

     The mpool_filter() function is intended to make transparent input and
     output processing of the pages possible. If the pgin function is speci-
     fied, it is called each time a buffer is read into the memory pool from
     the backing file. If the pgout function is specified, it is called each
     time a buffer is written into the backing file. Both functions are called
     with the pgcookie pointer, the page number, and a pointer to the page be-
     ing read or written.

     The function mpool_new() takes an MPOOL pointer, an address, and a set of
     flags as arguments. If a new page can be allocated, a pointer to the page
     is returned and the page number is stored into the pgnoaddr address. Oth-
     erwise, NULL is returned and errno is set. The flags value is formed by
     OR'ing the following values:

     MPOOL_PAGE_REQUEST
             Allocate a new page with a specific page number.

     MPOOL_PAGE_NEXT
             Allocate a new page with the next page number.

     The function mpool_delete() deletes the specified page from a pool and
     frees the page. It takes an MPOOL pointer and a page as arguments. The
     page must have been generated by mpool_new().

     The function mpool_get() takes an MPOOL pointer and a page number as ar-
     guments. If the page exists, a pointer to the page is returned. Other-
     wise, NULL is returned and errno is set. The flags parameter is not
     currently used.

     The function mpool_put() unpins the page referenced by pgaddr. pgaddr
     must be an address previously returned by mpool_get() or mpool_new(). The
     flags value is formed by OR'ing the following values:

     MPOOL_DIRTY
             The page has been modified and needs to be written to the backing
             file.

     mpool_put() returns 0 on success and -1 if an error occurs.

     The function mpool_sync() writes all modified pages associated with the
     MPOOL pointer to the backing file. mpool_sync() returns 0 on success and
     -1 if an error occurs.

     The mpool_close() function frees up any allocated memory associated with
     the memory pool cookie. Modified pages are not written to the backing
     file. mpool_close() returns 0 on success and -1 if an error occurs.

ERRORS

     The mpool_open() function may fail and set errno for any of the errors
     specified for the library routines fstat(2) and malloc(3), or the follow-
     ing:

     [ESPIPE]      The given file descriptor is a pipe.

     The mpool_get() function may fail and set errno for the following:

     [EINVAL]      The requested record doesn't exist.

     The mpool_new() and mpool_get() functions may fail and set errno for any
     of the errors specified for the library routines pread(2), pwrite(2), and
     malloc(3).

     The mpool_sync() function may fail and set errno for any of the errors
     specified for the library routine pwrite(2).

     The mpool_close() function may fail and set errno for any of the errors
     specified for the library routine free(3).

     The mpool_delete() always acts as if it succeeded.

SEE ALSO

     btree(3), dbopen(3), hash(3), recno(3)

MirOS BSD #10-current         February 25, 1999                              1

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