Description

   This routine uses the value specified in the guardsize argument
   to set the guardsize attribute of the thread attributes object
   specified in the attr argument.

   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, with its associated overflow warning area, can
   help a multithreaded program detect 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, following the thread's overflow warning area. If the
   thread attempts to write in the overflow warning area, a stack
   overflow exception occurs. Your program can catch this exception
   and continue processing as long as the thread does not attempt
   to write in the guard area. When any thread attempts to access
   a memory location within the guard area, a memory addressing
   violation occurs without the possibility of recovery.

   A new thread can be created with a default guardsize attribute
   value. This value is platform dependent, but will always be
   at least one "hardware protection unit" (that is, at least one
   page). For more information, see this guide's platform-specific
   appendixes.

   After this routine is called, due to platform-specific factors
   the Threads Library might reserve a larger guard area for the
   new thread than was specified in the guardsize argument. See this
   guide's platform-specific appendixes for more information.

   The Threads Library allows your program to specify the size of a
   thread stack's guard area for two reasons:

   o  When a thread allocates large data structures on its stack, a
      guard area with a size greater than the default size might be
      required to detect stack overflow.

   o  Overflow protection of a thread's stack can potentially waste
      system resources, such as for an application that creates a
      large number of threads that will never overflow their stacks.
      Your multithreaded program can conserve system resources
      by "turning off" a thread's stack guard area-that is, by
      specifying a guardsize attribute of zero.

   If a thread is created using a thread attributes object whose
   stackaddr attribute is set (using the pthread_attr_setstackaddr()
   routine), this routine ignores the object's guardsize attribute
   and provides no thread stack overflow warning or guard area for
   the new thread.