.\" Automatically generated by Pandoc 2.0.6
.\"
.TH "PMEM2_GET_DRAIN_FN" "3" "2022-08-25" "PMDK - pmem2 API version 1.0" "PMDK Programmer's Manual"
.hy
.\" SPDX-License-Identifier: BSD-3-Clause
.\" Copyright 2020, Intel Corporation
.SH NAME
.PP
\f[B]pmem2_get_drain_fn\f[]() \- get a drain function
.SH SYNOPSIS
.IP
.nf
\f[C]
#include\ <libpmem2.h>

typedef\ void\ (*pmem2_drain_fn)(void);

struct\ pmem2_map;

pmem2_drain_fn\ pmem2_get_drain_fn(struct\ pmem2_map\ *map);
\f[]
.fi
.SH DESCRIPTION
.PP
The \f[B]pmem2_get_drain_fn\f[]() function returns a pointer to a
function responsible for efficiently draining flushes (see
\f[B]pmem2_get_flush_fn\f[](3)) in the range owned by \f[I]map\f[].
Draining, in this context, means making sure that the flushes before
this operation won't be reordered after it.
While it is not strictly true, draining can be thought of as waiting for
previous flushes to complete.
.PP
If two (or more) mappings share the same drain function, it is safe to
call this function once for all flushes belonging to those mappings.
.SH RETURN VALUE
.PP
The \f[B]pmem2_get_drain_fn\f[]() function never returns NULL.
.PP
The \f[B]pmem2_get_drain_fn\f[]() for the same \f[I]map\f[] always
returns the same function.
This means that it's safe to cache its return value.
However, this function is very cheap (because it returns a precomputed
value), so caching may not be necessary.
.SH SEE ALSO
.PP
\f[B]pmem2_get_flush_fn\f[](3), \f[B]pmem2_get_persist_fn\f[](3),
\f[B]pmem2_map_new\f[](3), \f[B]libpmem2\f[](7) and
\f[B]<https://pmem.io>\f[]