NetBSD/lib/libpthread/tss.3

.\"	$NetBSD: tss.3,v 1.2 2019/04/27 10:57:11 wiz Exp $
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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 TSS 3
.Os
.Sh NAME
.Nm tss
.Nd thread-specific storage functions
.Sh LIBRARY
.Lb libpthread
.Sh SYNOPSIS
.In threads.h
.Vt "typedef" "void" "(*tss_dtor_t)" "(void *)"
.Ft int
.Fn tss_create "tss_t *key" "tss_dtor_t dtor"
.Ft void
.Fn tss_delete "tss_t key"
.Ft void *
.Fn tss_get "tss_t key"
.Ft int
.Fn tss_set "tss_t key" "void *val"
.Vt #define TSS_DTOR_ITERATIONS /* implementation specified */
.Sh DESCRIPTION
There are two groups of storage in C programs:
.Bl -dash
.It
local storage,
.It
global storage.
.El
.Pp
Multithreaded programs in C add the third group
.Sy thread-specific storage .
This data is private to thread and every entry of this type has an associated
.Dv tss_t
opaque key that is global to all threads in the process.
A thread using the
.Dv tss_t *
pointer accesses private data.
.Pp
The
.Fn tss_create
function creates a thread-specific storage with the
.Fa key
handler with optional destructor
.Fa dtor .
If the
.Fa dtor
parameter is not
.Dv NULL ,
then specified appropriate destructor will be called on thread termination.
The destructor is not called if a thread called the
.Fn tss_delete
function for the specified
.Fa key .
If, after all the destructors have been called for all
.Pf non- Dv NULL
values with associated destructors,
there are still some
.Pf non- Dv NULL
values with associated destructors,
then the process is repeated.
If, after at least
.Dv TSS_DTOR_ITERATIONS
iterations of destructor calls for outstanding
.Pf non- Dv NULL
values, there are still some
.Pf non- Dv NULL
values with associated destructors, the
.Nx
implementation stops calling further destructors.
The
.Xr thrd_exit 3
function must not be called from a destructor.
.Pp
The
.Fn tss_delete
function frees resources used by the thread-specific storage identified by the
.Fa key
object.
This function can be called inside the
.Fa dtor
destructor, however the destructor is not called by
.Fn tss_delete .
.Pp
The
.Fn tss_get
and
.Fn tss_set
functions are used to get and set thread-specific storage.
.Sh RETURN VALUES
The
.Fn tss_create
function returns
.Dv thrd_success
on success, otherwise
.Dv thrd_error
on failure.
.Pp
The
.Fn tss_delete
function returns no value.
.Pp
The
.Fn tss_get
returns pointer to thread-specific storage on success or
.Dv NULL
on failure.
.Pp
The
.Fn tss_set
function returns
.Dv thrd_success
on success, otherwise
.Dv thrd_error
on failure.
.Sh SEE ALSO
.Xr pthread_getspecific 3 ,
.Xr pthread_key_create 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