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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 [email protected]

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