SET_TID_ADDRESSSection: Linux Programmer's Manual (2)
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NAMEset_tid_address - set pointer to thread ID
#include <linux/unistd.h> long set_tid_address(int *tidptr);
DESCRIPTIONThe kernel keeps for each process two values called set_child_tid and clear_child_tid that are NULL by default.
set_child_tidIf a process is started using clone(2) with the CLONE_CHILD_SETTID flag, set_child_tid is set to child_tidptr, the fifth parameter of that system call.
clear_child_tidIf a process is started using clone(2) with the CLONE_CHILD_CLEARTID flag, clear_child_tid is set to child_tidptr, the fifth parameter 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 VALUEset_tid_address() always returns the PID of the calling process.
ERRORSset_tid_address() always succeeds.
VERSIONSThis call is present since Linux 2.5.48. Details as given here are valid since Linux 2.5.49.
CONFORMING TOThis system call is Linux specific.
SEE ALSOclone(2), futex(2)
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