set_tid_address (2) - Linux Man Pages
set_tid_address: set pointer to thread ID
set_tid_address - set pointer to thread ID
#include <linux/unistd.h> long set_tid_address(int *tidptr);
DESCRIPTIONFor 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.
- 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.
- 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:
always returns the caller's thread ID.
This call is present since Linux 2.5.48.
Details as given here are valid since Linux 2.5.49.
This system call is Linux-specific.
Glibc does not provide a wrapper for this system call; call it using
This page is part of release 5.05 of the Linux
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