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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
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SET_TID_ADDRESS(2) Linux Programmer's Manual SET_TID_ADDRESS(2)
set_tid_address - set pointer to thread ID
#include <linux/unistd.h>
pid_t set_tid_address(int *tidptr);
Note: There is no glibc wrapper for this system call; see NOTES.
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.
set_tid_address() always returns the caller's thread ID.
set_tid_address() always succeeds.
This call is present since Linux 2.5.48. Details as given here
are valid since Linux 2.5.49.
This system call is Linux-specific.
Glibc does not provide a wrapper for this system call; call it
using syscall(2).
clone(2), futex(2), gettid(2)
This page is part of release 5.10 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/.
Linux 2020-12-21 SET_TID_ADDRESS(2)
Pages that refer to this page: clone(2), prctl(2), syscalls(2), futex(7)
Copyright and license for this manual page
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