2. EL 6 ELS
  3. man-pages
  4. set_tid_address(2)

Scroll to navigation

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

The kernel keeps for each process two values called set_child_tid and clear_child_tid that are NULL by default.

set_child_tid

If a process is started using clone(2) with the CLONE_CHILD_SETTID flag, set_child_tid is set to child_tidptr, the fifth 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 child_tidptr, the fifth argument of that system call.

The system call set_tid_address() sets the clear_child_tid value for the calling process to tidptr.

When clear_child_tid is set, and the process exits, and the process was sharing memory with other processes or threads, then 0 is written at this address, and a futex(child_tidptr, FUTEX_WAKE, 1, NULL, NULL, 0); call is done. (That is, wake a single process waiting on this futex.) Errors are ignored.

RETURN VALUE

set_tid_address() always returns the PID of the calling process.

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.

SEE ALSO

clone(2), futex(2)

COLOPHON

This page is part of release 3.22 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/.

2004-09-10 Linux