SET_TID_ADDRESS
Section: Linux Programmer's Manual (2)
Updated: 2017-09-15
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NAME
set_tid_address - set pointer to thread ID
SYNOPSIS
#include <linux/unistd.h>
long set_tid_address(int *tidptr);
Note:
There is no glibc wrapper for this system call; see NOTES.
DESCRIPTION
For each thread, 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 thread 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 thread does
is to write its thread ID at this address.
- clear_child_tid
-
If a thread 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 thread to
tidptr.
When a thread whose
clear_child_tid
is not NULL terminates, then,
if the thread is sharing memory with other 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 thread that
is performing a futex wait on the memory location.
Errors from the futex wake operation are ignored.
RETURN VALUE
set_tid_address()
always returns the caller's thread ID.
ERRORS
set_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.
NOTES
Glibc does not provide a wrapper for this system call; call it using
syscall(2).
SEE ALSO
clone(2),
futex(2),
gettid(2)
COLOPHON
This page is part of release 4.13 of the Linux
man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
https://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- VERSIONS
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
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