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SET_TID_ADDRESS

Section: Linux Programmer's Manual (2)
Updated: 2004-09-10
Index Return to Main Contents

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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 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 child_tidptr, the fifth argument 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)  

COLOPHON

This page is part of release 3.35 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://man7.org/linux/man-pages/.

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Index

NAME

SYNOPSIS

DESCRIPTION

set_child_tid

clear_child_tid

RETURN VALUE

ERRORS

VERSIONS

CONFORMING TO

SEE ALSO

COLOPHON

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