set_tid_address(2) — Linux manual page


SET_TID_ADDRESS(2)        Linux Programmer's Manual       SET_TID_ADDRESS(2)

NAME         top

       set_tid_address - set pointer to thread ID

SYNOPSIS         top

       #include <linux/unistd.h>

       long set_tid_address(int *tidptr);

       Note: There is no glibc wrapper for this system call; see NOTES.

DESCRIPTION         top

       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.

              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.

              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         top

       set_tid_address() always returns the caller's thread ID.

ERRORS         top

       set_tid_address() always succeeds.

VERSIONS         top

       This call is present since Linux 2.5.48.  Details as given here are
       valid since Linux 2.5.49.

CONFORMING TO         top

       This system call is Linux-specific.

NOTES         top

       Glibc does not provide a wrapper for this system call; call it using

SEE ALSO         top

       clone(2), futex(2), gettid(2)

COLOPHON         top

       This page is part of release 5.08 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

Linux                            2017-09-15               SET_TID_ADDRESS(2)

Pages that refer to this page: clone2(2)__clone2(2)clone(2)clone3(2)prctl(2)syscalls(2)futex(7)