Manpage of MPOOL
MPOOLSection: Linux Programmer's Manual (3)
NAMEmpool - shared memory buffer pool
#include <db.h>#include <mpool.h>MPOOL *mpool_open(DBT *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);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);
DESCRIPTIONNote well: This page documents interfaces provided in glibc up until version 2.1. Since version 2.2, glibc no longer provides these interfaces. Probably, you are looking for the APIs provided by the libdblibrary instead.
Mpoolis 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 keyargument 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 keyis NULL, the buffers are mapped into private memory. The fdargument is a file descriptor for the underlying file, which must be seekable. If keyis non-NULL and matches a file already being mapped, the fdargument is ignored.
The pagesizeargument is the size, in bytes, of the pages into which the file is broken up. The maxcacheargument is the maximum number of pages from the underlying file to cache at any one time. This value is not relative 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 pginfunction is specified, it is called each time a buffer is read into the memory pool from the backing file. If the pgoutfunction is specified, it is called each time a buffer is written into the backing file. Both functions are called with the pgcookiepointer, the page number and a pointer to the page to being read or written.
The function mpool_new() takes an MPOOLpointer and an address as arguments. If a new page can be allocated, a pointer to the page is returned and the page number is stored into the pgnoaddraddress. Otherwise, NULL is returned and errnois set.
The function mpool_get() takes an MPOOLpointer and a page number as arguments. If the page exists, a pointer to the page is returned. Otherwise, NULL is returned and errnois set. The flagsargument is not currently used.
The function mpool_put() unpins the page referenced by pgaddr. pgaddrmust be an addressly returned by mpool_get() or mpool_new(). The flag value is specified by ORing any of the following values:
- 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 MPOOLpointer to the backing file. mpool_sync() returns 0 on success and -1 if an error occurs.
The mpool_close() function free's up any allocated memory associated with the memory pool cookie. Modified pages are notwritten to the backing file. mpool_close() returns 0 on success and -1 if an error occurs.
ERRORSThe mpool_open() function may fail and set errnofor any of the errors specified for the library routine malloc(3).
The mpool_get() function may fail and set errnofor the following:
- The requested record doesn't exist.
The mpool_sync() function may fail and set errnofor any of the errors specified for the library routine write(2).
The mpool_close() function may fail and set errnofor any of the errors specified for the library routine free(3).
CONFORMING TONot in POSIX.1. Present on the BSDs.
SEE ALSObtree(3), dbopen(3), hash(3), recno(3)
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