set_tid_address(2)

1SET_TID_ADDRESS(2)         Linux Programmer's Manual        SET_TID_ADDRESS(2)
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NAME

6       set_tid_address - set pointer to thread ID
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SYNOPSIS

9       #include <linux/unistd.h>
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11       long set_tid_address(int *tidptr);
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DESCRIPTION

14       The  kernel  keeps for each process two values called set_child_tid and
15       clear_child_tid that are NULL by default.
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17   set_child_tid
18       If a process is started  using  clone(2)  with  the  CLONE_CHILD_SETTID
19       flag,  set_child_tid is set to child_tidptr, the fifth argument of that
20       system call.
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22       When set_child_tid is set, the very first thing the new process does is
23       writing its PID at this address.
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25   clear_child_tid
26       If  a  process  is started using clone(2) with the CLONE_CHILD_CLEARTID
27       flag, clear_child_tid is set to child_tidptr,  the  fifth  argument  of
28       that system call.
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30       The  system  call  set_tid_address() sets the clear_child_tid value for
31       the calling process to tidptr.
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33       When clear_child_tid is set, and the process exits, and the process was
34       sharing  memory  with  other processes or threads, then 0 is written at
35       this address, and a futex(child_tidptr, FUTEX_WAKE, 1, NULL, NULL,  0);
36       call  is done.  (That is, wake a single process waiting on this futex.)
37       Errors are ignored.
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RETURN VALUE

40       set_tid_address() always returns the PID of the calling process.
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ERRORS

43       set_tid_address() always succeeds.
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VERSIONS

46       This call is present since Linux 2.5.48.  Details  as  given  here  are
47       valid since Linux 2.5.49.
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CONFORMING TO

50       This system call is Linux-specific.
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COLOPHON

56       This  page  is  part of release 3.25 of the Linux man-pages project.  A
57       description of the project, and information about reporting  bugs,  can
58       be found at http://www.kernel.org/doc/man-pages/.
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62Linux                             2004-09-10                SET_TID_ADDRESS(2)