set_tid_address
NAME
set_tid_address - set pointer to thread ID
SYNOPSIS
#include <linux/unistd.h> I 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 R 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 R child_tidptr , the fifth parameter of that system call.The system call
R set_tid_address ()
sets the
clear_child_tid
value for the calling process to
R 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
R set_tid_address ()
always returns the PID of the calling process.
ERRORS
R 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.
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