.\"	$NetBSD: mtx.3,v 1.2 2019/04/27 10:57:11 wiz Exp $
.\"
.\" Copyright (c) 2016 The NetBSD Foundation, Inc.
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Kamil Rytarowski.
.\"
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.Dd October 16, 2016
.Dt MTX 3
.Os
.Sh NAME
.Nm mtx
.Nd mutex functions
.Sh LIBRARY
.Lb libpthread
.Sh SYNOPSIS
.In threads.h
.Ft void
.Fn mtx_destroy "mtx_t *mtx"
.Ft int
.Fn mtx_init "mtx_t *mtx" "int type"
.Ft int
.Fn mtx_lock "mtx_t *mtx"
.Ft int
.Fn mtx_timedlock "mtx_t *__restrict mtx" "const struct timespec *__restrict ts"
.Ft int
.Fn mtx_trylock "mtx_t *mtx"
.Ft int
.Fn mtx_unlock "mtx_t *mtx"
.Sh DESCRIPTION
The
.Fn mtx_destroy
function releases the resources of
.Fa mtx .
It is not allowed to block the same
.Fa mtx
during the
.Fn mtx_destroy
call.
.Pp
The
.Fn mtx_init
function initialized the
.Fa mtx
object uniquely identificable with the
.Fa type
properties.
The allowed values of
.Fa type
are as follows:
.Bl -column "mtx_plain | mtx_recursive"
.It Sy "Type"                    Ta Sy "Description"
.It Dv mtx_plain                 Ta basic mutex
.It Dv mtx_timed                 Ta mutex with timeout support
.It Dv mtx_plain | Dv mtx_recursive Ta basic recursive mutex
.It Dv mtx_timed | Dv mtx_recursive Ta recursive mutex with timeout support
.El
.Pp
The underlying
.Nx
implementation of mutex types does not distinguish between
.Dv mtx_plain
and
.Dv mtx_timed ,
however portable code must keep the distinction.
.Pp
The
.Fn mtx_lock
function locks the
.Fa mtx
object.
It is required to never lock the same
.Fa mtx
object without the
.Dv mtx_recursive
property multiple times.
If the
.Fa mtx
object is already locked by another thread,
the caller of
.Fa mtx_lock
blocks until the lock becomes available.
.Pp
The
.Fn mtx_timedlock
function tries to lock the
.Fa mtx
object.
In case of blocked resource by another thread,
this call blocks for the specified timeout in the
.Fa ts
argument.
The timeout argument is
.Dv TIME_UTC
based time of
.Dv timespec
type.
It is required to never lock the same
.Fa mtx
object without the
.Dv mtx_recursive
property multiple times.
In portable code, a
.Fa mtx
object with the
.Dv mtx_recursive
property must be used in such a case.
.Pp
The
.Fn mtx_trylock
function call attempts to lock the
.Fa mtx
object.
This function does not block if another thread already locked the
.Fa mtx
object, but immediately returns indicating proper status.
.Pp
The
.Fn mtx_unlock
function unlocks the
.Fa mtx
object.
This call must be preceded with a matching
.Fn mtx_lock
call in the same thread.
.Sh RETURN VALUES
The
.Fn mtx_destroy
function returns no value.
.Pp
The
.Fn mtx_init
function returns
.Dv thrd_success
on success or
.Dv thrd_error
on failure.
.Pp
The
.Fn mtx_lock
function returns
.Dv thrd_success
on success or
.Dv thrd_error
on failure.
.Pp
The
.Fn mtx_lock
function returns
.Dv thrd_success
on success,
otherwise
.Dv thrd_timedout
to indicate that system time has reached or exceeded the time specified in
.Dv ts ,
or
.Dv thrd_error
on failure.
.Pp
The
.Fn mtx_trylock
function returns
.Dv thrd_success
on success,
otherwise
.Dv thrd_timedout
to indicate that
.Fa mtx
object is already locked, or
.Dv thrd_error
on failure.
.Pp
The
.Fn mtx_unlock
function returns
.Dv thrd_success
on success,
otherwise
.Dv thrd_timedout
to indicate that
.Fa mtx
object is already locked, or
.Dv thrd_error
on failure.
.Sh SEE ALSO
.Xr pthread_mutex 3 ,
.Xr threads 3
.Sh STANDARDS
The
.Nm
interface conforms to
.St -isoC-2011 .
.Sh HISTORY
This interface first appeared in
.Nx 9 .
.Sh AUTHORS
.An Kamil Rytarowski Aq Mt kamil@NetBSD.org