SET_TID_ADDRESS(2) - Linux man page online | System calls

Set pointer to thread ID.

SET_TID_ADDRESS(2) Linux Programmer's Manual SET_TID_ADDRESS(2)


set_tid_address - set pointer to thread ID


#include <linux/unistd.h> long set_tid_address(int *tidptr); Note: There is no glibc wrapper for this system call; see NOTES.


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.


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 syscall(2).


clone(2), futex(2), gettid(2)


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Linux 2017-09-15 SET_TID_ADDRESS(2)
This manual Reference Other manuals
set_tid_address(2) referred by clone(2) | futex(7) | prctl(2) | syscalls(2)
refer to clone(2) | futex(2) | gettid(2) | syscall(2)
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