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set_tid_address — set pointer to thread ID
#include <linux/unistd.h>
long
set_tid_address( |
int *tidptr); |
For each process, the kernel maintains two attributes
(addresses) called set_child_tid and clear_child_tid. These two
attributes contain the value NULL by default.
set_child_tidIf a process is started using clone(2) with the
CLONE_CHILD_SETTID flag,
set_child_tid
is set to the value passed in the ctid argument of that
system call.
When set_child_tid is set,
the very first thing the new process does is writing
its PID at this address.
clear_child_tidIf a process is started using clone(2) with the
CLONE_CHILD_CLEARTID
flag, clear_child_tid is set
to the value passed in the ctid argument of that
system call.
The system call set_tid_address() sets the clear_child_tid value for the
calling process to tidptr.
When a process whose clear_child_tid is not NULL
terminates, then, if the process is sharing memory with other
processes or threads, then 0 is written at the address
specified in clear_child_tid and the
kernel performs the following operation:
futex(clear_child_tid, FUTEX_WAKE, 1, NULL, NULL, 0);
The effect of this operation is to wake a single process that is performing a futex wait on the memory location. Errors from the futex wake operation are ignored.
This call is present since Linux 2.5.48. Details as given here are valid since Linux 2.5.49.
This page is part of release 3.52 of the Linux man-pages project. A
description of the project, and information about reporting
bugs, can be found at
http://www.kernel.org/doc/man−pages/.
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Copyright (C) 2004 Andries Brouwer (aebcwi.nl) %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END |