NetBSD/share/man/man9/pool.9

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.\" $NetBSD: pool.9,v 1.5 1998/04/22 07:14:33 ross Exp $
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.\" Copyright (c) 1997 The NetBSD Foundation, Inc.
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Paul Kranenburg.
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.Dd December 4, 1997
.Dt POOL 9
.Os NetBSD
.Sh NAME
.Nm pool_create ,
.Nm pool_destroy ,
.Nm pool_get ,
.Nm pool_put ,
.Nm pool_prime
.Nd resource-pool manager
.Sh SYNOPSIS
.Fd #include <sys/malloc.h>
.Fd #include <sys/pool.h>
.Ft struct pool *
.Fn pool_create "size_t size" "int nitems" "char *wchan" "int mtype" "caddr_t storage"
.Ft void *
.Fn pool_get "struct pool *pp" "int flags"
.Ft void
.Fn pool_put "struct pool *pp" "void *item"
.Ft int
.Fn pool_prime "struct pool *pp" "int nitems" "caddr_t storage"
.Fn POOL_STORAGE_SIZE "size" "nitems"
.Sh DESCRIPTION
These utility routines provide management of pools of fixed-sized
areas of memory. Resource pools set aside an amount of memory for
exclusive use by the resource pool owner. This can be used by
applications to guarantee the availability of a minimum amount of memory
needed to continue operation independent of the memory resources
currently available from the system-wide memory allocator
.Po
.Xr malloc 9
.Pc .
The pool manager can optionally obtain temporary memory through
.Xr malloc 9
for extra pool items in case the number of allocations exceeds
the nominal number of pool items managed by a pool resource.
This temporary memory will be automatically returned to the system
at a later time.
.Pp
The function
.Fn pool_create
initializes a resource pool and returns a handle to it. The
arguments are:
.Pp
.Bl -tag -offset indent -width "nitems"
.It Fa size
specifies the size of the memory items managed by the pool.
.It Fa nitems
specifies the number of memory items that are allocated to
the pool at creation time. This number may be zero, in which case
.Fn pool_prime
must be used at a later time to add items to the pool.
.It Fa wchan
the
.Sq wait channel
passed on to
.Xr tsleep 9
if
.Fn pool_get
must wait for items to be returned to the pool.
.It Fa mtype
the memory tag passed to
.Xr malloc 9
when allocating memory for pool items.
.It Fa storage
Optional storage provided by the caller to use in lieu of
.Xr malloc 9
for both the pool handle and all pool items.
.El
.Pp
If not enough memory is available to create the pool resource,
.Fn pool_create
returns
.Dv NULL .
If the
.Fa storage
parameter is used, the client is responsible for providing enough storage
to accommodate the number of pool items specified by
.Fa nitems ,
as well as the space required by the pool's administrative overhead
.Pq i.e. the pool handle .
The macro
.Fn POOL_STORAGE_SIZE "size" "nitems"
can be used to determine the amount of storage needed to setup a pool,
given the size and number of the pool items.
.Pp
.Fn pool_get
allocates an item from the pool and returns a pointer to it.
.Bl -tag -offset indent -width "flags"
.It Fa pp
The handle identifying the pool resource instance.
.It Fa flags
A combination of
.Dv PR_MALLOCOK
and
.Dv PR_WAITOK ,
that define behaviour in case the pooled resources are depleted.
If
.Dv PR_MALLOCOK
is given, an attempt will be made to allocate supplemental memory by using
.Xr malloc 9 .
If no resources are available and
.Dv PR_WAITOK
is given, this function will wait until items are returned to the pool,
otherwise
.Fn pool_get
returns
.Dv NULL .
Undefined behaviour results if
.Dv PR_MALLOCOK
is specified on a pool handle that was created using client-provided
storage.
.El
.Pp
.Fn pool_put
returns the pool item pointed at by
.Fa item
to the resource pool identified by the pool handle
.Fa pp .
If the number of available items in the pool exceeds the nominal pool
size and there are no out-standing requests for pool items, the excess
items will be returned to the system by using
.Xr free 9 .
.Bl -tag -offset indent -width "item"
.It Fa pp
The handle identifying the pool resource instance.
.It Fa item
A pointer to a pool item previously obtained by
.Fn pool_get .
.El
.Pp
.Fn pool_prime
adds items to the pool.
.Bl -tag -offset indent -width "nitems"
.It Fa pp
The handle identifying the pool resource instance.
.It Fa nitems
The number of items to add to the pool. Storage for the pool items can be
passed in the
.Fa storage
argument. If this parameter is
.Dv NULL ,
the items are allocated by using
.Xr malloc 9 .
This function may return
.Dv ENOMEM
in case the requested number of items could not be allocated. Otherwise,
the return value is 0.
.El
.Pp
Note that undefined behaviour results when mixing the storage providing
methods supported by the pool resource routines.
.Sh RETURN VALUES
.Sh EXAMPLES
.Sh CODE REFERENCES
.Pp
The pool manager is implemented in the file
.Nm sys/kern/subr_pool.c .
.Pp
.Sh AUTHOR
.Sh SEE ALSO
.Xr malloc 9 ,
.Xr free 9 .
.Sh HISTORY
The
.Nx
pool manager appeared in
.Nx 1.4 .