set_tid_address — set pointer to thread ID
#include <linux/unistd.h>
long
set_tid_address( |
int *tidptr); |
The kernel keeps for each process two values called
set_child_tid and
clear_child_tid
that are NULL by default.
If a process is started using clone(2) with the
CLONE_CHILD_SETTID flag,
set_child_tid is
set to child_tidptr, the fifth
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.
If a process is started using clone(2) with the
CLONE_CHILD_CLEARTID flag,
clear_child_tid
is set to child_tidptr, the fifth
argument of that system call.
The system call set_tid_address() sets the clear_child_tid value for
the calling process to tidptr.
When clear_child_tid is set, and
the process exits, and the process was sharing memory with
other processes or threads, then 0 is written at this
address, and a futex(child_tidptr, FUTEX_WAKE, 1, NULL,
NULL, 0); call is done. (That is, wake a single
process waiting on this futex.) Errors 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 3.33 of the Linux man-pages project. A
description of the project, and information about reporting
bugs, can be found at http://man7.org/linux/man-pages/.
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Copyright (C) 2004 Andries Brouwer (aebcwi.nl) 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 Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date.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. |