Description

   This routine obtains the value of the guardsize attribute of
   the thread attributes object specified in the attr argument and
   stores it in the location specified by the guardsize argument.
   The specified attributes object must already be initialized at
   the time this routine is called.

   When creating a thread, use a thread attributes object to specify
   nondefault values for thread attributes. The guardsize attribute
   of a thread attributes object specifies the minimum size (in
   bytes) of the guard area for the stack of a new thread.

   A guard area can help a multithreaded program detect the overflow
   of a thread's stack. A guard area is a region of no-access memory
   that the Threads Library allocates at the overflow end of the
   thread's stack. When any thread attempts to access a memory
   location within this region, a memory addressing violation
   occurs.

   Note that the value of the guardsize attribute of a particular
   thread attributes object does not necessarily correspond to the
   actual size of the guard area of any existing thread in your
   multithreaded program.