Why is __sglue initialized in _cygtls::init_thread()?

[Sebastian Huber]

Hello,

I have a question to _cygtls::init_thread():

void
_cygtls::init_thread (void *x, DWORD (*func) (void *, void *))
{
   if (x)
     {
       memset (this, 0, sizeof (*this));
       _REENT_INIT_PTR (&local_clib);
       stackptr = stack;
       altstack.ss_flags = SS_DISABLE;
       if (_GLOBAL_REENT)
	{
	  local_clib._stdin = _GLOBAL_REENT->_stdin;
	  local_clib._stdout = _GLOBAL_REENT->_stdout;
	  local_clib._stderr = _GLOBAL_REENT->_stderr;
	  if (_GLOBAL_REENT->__cleanup)
	    local_clib.__cleanup = _cygtls::cleanup_early;
	  local_clib.__sglue._niobs = 3;
	  local_clib.__sglue._iobs = &_GLOBAL_REENT->__sf[0];
	}
     }

Why is __sglue initialized here? It seems to be unused in general for 
local_clib.__sglue:

1. The __sglue::next member was still NULL, so even if someone calls 
_reclaim_reent(), cleanup_glue() would not get called.

2. FILE objects are added to the __sglue list only by __sfp().  This 
function only uses the __sglue member of _GLOBAL_REENT.

It could be used by _fcloseall_r() through _fwalk_reent() which seems to 
be unused by Cygwin.

It could be used by __fp_lock_all() and __fp_unlock_all() through 
_fwalk() which is used only by Cygwin in the pthread::atfork*() functions.

It could be used by _cleanup_r() through _fwalk_reent().

In the above three cases the file walk would operate on the three FILE 
objects in _GLOBAL_REENT->__sf. I would like to change the __sglue 
handling, so it would be great if someone could explain the Cygwin use 
case for the __sglue initialization in _cygtls::init_thread().

-- 
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