/REENTRANCY=option D=/REENTRANCY=NONE

 /[NO]REENTRANCY

 Tells the VSI Fortran RTL whether the program will be relying on
 threaded or asynchronous (AST) reentrancy.

 /NOREENTRANCY specifies that the program will not be relying on
 threaded or asynchronous (AST) reentrancy.  So, the RTL will not
 guard against such interrupts inside the RTL.  This is the same as
 specifying /REENTRANCY=NONE (the default).

 ASYNC
   Specifies that the program may contain asynchronous (AST)
   handlers that could call the RTL.  This causes the RTL to guard
   against AST interrupts inside its own critical regions.

   This option is ignored for applications running on versions of
   OpenVMS earlier than Version 7.0.

 NONE
   Specifies that the program will not be relying on threaded or
   asynchronous (AST) reentrancy.  So, the RTL will not guard
   against such interrupts inside the RTL.  This is the default and
   is the same as specifying /NOREENTRANCY.

 THREADED
   Specifies that the program is multithreaded, such as programs
   using the DECthreads library.  This causes the RTL to use thread
   locking to guard its own critical regions.

   This option is ignored for applications running on versions of
   OpenVMS earlier than Version 7.0.