mpool(3POSIX)

NAME | SYNOPSIS | FEATURES | DESCRIPTION | ERRORS | ATTRIBUTES | SEE ALSO | RESTRICTIONS

NAME

mpool- shared memory buffer pool

SYNOPSIS

#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, u_int flags);
int mpool_put(MPOOL *mp, void *pgaddr, u_int flags);
int mpool_sync(MPOOL *mp);
int mpool_close(MPOOL *mp);

FEATURES

UFS

DESCRIPTION

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

The mpool_open function initializes a memory pool. The key argument is the byte string used to negotiate between multiple processes requiring 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 ignored.

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 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 enable transparent input and output processing of the pages. If the pgin function is specified, 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 using the pgcookie pointer, the page number and a pointer to the page being read or written to.

The mpool_new function takes a MPOOL pointer 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 in the pgnoaddr address. Otherwise, a NULL value is returned and errno is set to indicqte the error condition..

The mpool_get function takes a MPOOL pointer and a page number as arguments. If the page exists, a pointer to the page is returned. Otherwise, a NULL value is returned and errno is set to indicate the error condition. The flags parameter is not currently used.

The mpool_put function un-pins the page referenced by pgaddr. The pgaddr must be an address previously returned by mpool_get or mpool_new. The flag value is specified by or ing any of the following values:

MPOOL_DIRTY

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

The mpool_put function returns 0 on success and -1 if an error occurs.

The mpool_sync function 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. The mpool_close returns 0 on success and -1 if an error occurs.

ERRORS

The mpool_open function may fail and set errno to any of the errors specified for the library routine malloc(3).

The mpool_get function may fail and set errno to the following error condition:

[EINVAL]

The requested record does not exist.

The mpool_new and mpool_get functions may fail and set errno to any of the errors specified for the library routines read(2POSIX), write(2POSIX), and malloc(3STDC).

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

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

ATTRIBUTES

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE	ATTRIBUTE VALUE
Interface Stability	Evolving

SEE ALSO

read(2POSIX), write(2POSIX), free(3STDC), malloc(3STDC), dbopen(3POSIX), btree(3POSIX), hash(3POSIX), recno(3POSIX)

RESTRICTIONS

These library calls do not support multi-threaded applications.

NAME | SYNOPSIS | FEATURES | DESCRIPTION | ERRORS | ATTRIBUTES | SEE ALSO | RESTRICTIONS