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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);

     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_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 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  per-
     forming  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 4.16 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 2017-09-15 SET_TID_ADDRESS(2)