установить указатель на идентификатор потока (set pointer to thread ID)
Имя (Name)
set_tid_address - set pointer to thread ID
Синопсис (Synopsis)
#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).
Описание (Description)
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.
Возвращаемое значение (Return value)
set_tid_address() always returns the caller's thread ID.
Ошибки (Error)
set_tid_address() always succeeds.
Версии (Versions)
This call is present since Linux 2.5.48. Details as given here
are valid since Linux 2.5.49.
Стандарты (Conforming to)
This system call is Linux-specific.
Смотри также (See also)
clone(2), futex(2), gettid(2)
