mirror of https://github.com/mkerrisk/man-pages
89 lines
2.6 KiB
Groff
89 lines
2.6 KiB
Groff
.\" Copyright (C) 2004 Andries Brouwer (aeb@cwi.nl)
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.TH SET_TID_ADDRESS 2 2004-09-10 "Linux 2.6" "Linux Programmer's Manual"
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.SH NAME
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set_tid_address \- set pointer to thread ID
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.SH SYNOPSIS
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.nf
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.B #include <linux/unistd.h>
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.sp
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.BI "long set_tid_address(int *" tidptr );
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.SH DESCRIPTION
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The kernel keeps for each process two values called
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.I set_child_tid
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and
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.I clear_child_tid
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that are NULL by default.
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.SS set_child_tid
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If a process is started using
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.BR clone (2)
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with the
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.B CLONE_CHILD_SETTID
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flag,
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.I set_child_tid
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is set to
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.IR child_tidptr ,
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the fifth parameter of that system call.
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.LP
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When
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.I set_child_tid
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is set, the very first thing the new process does
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is writing its PID at this address.
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.SS clear_child_tid
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If a process is started using
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.BR clone (2)
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with the
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.B CLONE_CHILD_CLEARTID
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flag,
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.I clear_child_tid
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is set to
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.IR child_tidptr ,
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the fifth parameter of that system call.
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.LP
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The system call
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.BR set_tid_address ()
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sets the
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.I clear_child_tid
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value for the calling process to
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.IR tidptr .
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.LP
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When
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.I clear_child_tid
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is set, and the process exits, and the process was sharing memory
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with other processes or threads, then 0 is written at this address,
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and a
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.I futex(child_tidptr, FUTEX_WAKE, 1, NULL, NULL, 0);
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call is done. (That is, wake a single process waiting on this futex.)
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Errors are ignored.
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.SH "RETURN VALUE"
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.BR set_tid_address ()
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returns the PID of the current process.
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.SH HISTORY
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This call is present since Linux 2.5.48.
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Details as given here are valid since Linux 2.5.49.
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.SH "CONFORMING TO"
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This system call is Linux specific.
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.SH "SEE ALSO"
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.BR clone (2),
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.BR futex (2)
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