SET_TID_ADDRESS(2) Linux Programmer's Manual SET_TID_ADDRESS(2)NAME
set_tid_address - set pointer to thread ID
SYNOPSIS
#include <linux/unistd.h>
long set_tid_address(int *tidptr);
DESCRIPTION
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_tid
If a process is started using clone(2) with the CLONE_CHILD_SET‐
TID 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_tid
If 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 per‐
forming a futex wait on the memory location. Errors from the futex
wake operation are ignored.
RETURN VALUEset_tid_address() always returns the PID of the calling process.
ERRORSset_tid_address() always succeeds.
VERSIONS
This call is present since Linux 2.5.48. Details as given here are
valid since Linux 2.5.49.
CONFORMING TO
This system call is Linux-specific.
SEE ALSOclone(2), futex(2)COLOPHON
This page is part of release 3.55 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/.
Linux 2012-07-19 SET_TID_ADDRESS(2)
