SET_TID_ADDRESS man page on Hurd

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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);

DESCRIPTION
       For  each  process,  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 process 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 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 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 process to tidptr.

       When  a	process whose clear_child_tid is not NULL terminates, then, if
       the process is sharing memory with other processes or 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 process 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 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 3.55 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/.

Linux				  2012-07-19		    SET_TID_ADDRESS(2)
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