Manpage of SET_TID_ADDRESS

SET_TID_ADDRESS

Section: Linux Programmer's Manual (2)
Updated: 2017-09-15
Index
 

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_tidand 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_SETTIDflag, set_child_tidis set to the value passed in the ctidargument of that system call.
When set_child_tidis 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_CLEARTIDflag, clear_child_tidis set to the value passed in the ctidargument of that system call.

The system call set_tid_address() sets the clear_child_tidvalue for the calling thread to tidptr.

When a thread whose clear_child_tidis not NULL terminates, then, if the thread is sharing memory with other threads, then 0 is written at the address specified in clear_child_tidand 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)


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
VERSIONS
CONFORMING TO
NOTES
SEE ALSO

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