NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | STANDARDS | HISTORY | SEE ALSO | COLOPHON |
|
|
set_tid_address(2) System Calls Manual set_tid_address(2)
set_tid_address - set pointer to thread ID
Standard C library (libc, -lc)
#include <sys/syscall.h> /* Definition of SYS_* constants */ #include <unistd.h> pid_t syscall(SYS_set_tid_address, int *tidptr); Note: glibc provides no wrapper for set_tid_address(), necessitating the use of syscall(2).
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. set_child_tid 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. clear_child_tid 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.
set_tid_address() always returns the caller's thread ID.
set_tid_address() always succeeds.
Linux.
Linux 2.5.48. Details as given here are valid since Linux 2.5.49.
clone(2), futex(2), gettid(2)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.9.1.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2024-06-26. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
Linux man-pages 6.9.1 2024-05-02 set_tid_address(2)
Pages that refer to this page: clone(2), PR_GET_TID_ADDRESS(2const), syscalls(2), futex(7)