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Update libthr(3) man page to reflect the work done to support dlopen.

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Noted and reviewed by:	bdrewery
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
This commit is contained in:
Konstantin Belousov 2015-02-12 17:16:54 +00:00
parent fee04ef7a9
commit e50def75bd
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=278627
1 changed files with 11 additions and 31 deletions
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42
lib/libthr/libthr.3
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@ -1,5 +1,5 @@
.\" Copyright (c) 2005 Robert N. M. Watson
.\" Copyright (c) 2014 The FreeBSD Foundation, Inc.
.\" Copyright (c) 2014,2015 The FreeBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" Part of this documentation was written by
@ -29,7 +29,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd September 26, 2014
.Dd February 12, 2015
.Dt LIBTHR 3
.Os
.Sh NAME
@ -200,45 +200,25 @@ Bigger values reduce the frequency of the FIFO discipline.
The value must be between 0 and 255.
.El
.Sh INTERACTION WITH RUN-TIME LINKER
The
On load,
.Nm
library must appear before
.Li libc
in the global order of depended objects.
.Pp
Loading
.Nm
with the
.Xr dlopen 3
call in the process after the program binary is activated
is not supported, and causes miscellaneous and hard-to-diagnose misbehaviour.
This is due to
.Nm
interposing several important
.Li libc
symbols to provide thread-safe services.
In particular,
.Dv errno
and the locking stubs from
.Li libc
are affected.
This requirement is currently not enforced.
.Pp
If the program loads any modules at run-time, and those modules may require
threading services, the main program binary must be linked with
.Li libpthread ,
even if it does not require any services from the library.
installs interposing handlers into the hooks exported by
.Li libc .
The interposers provide real locking implementation instead of the
stubs for single-threaded processes in
.Li ,
cancellation support and some modifications to the signal operations.
.Pp
.Nm
cannot be unloaded; the
.Xr dlclose 3
function does not perform any action when called with a handle for
.Nm .
One of the reasons is that the interposing of
One of the reasons is that the internal interposing of
.Li libc
functions cannot be undone.
.Sh SIGNALS
The implementation also interposes the user-installed
The implementation interposes the user-installed
.Xr signal 3
handlers.
This interposing is done to postpone signal delivery to threads which