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
parameter 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
parameter 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)
Copyright (C) 2004 Andries Brouwer (aeb@cwi.nl)
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