Int 2A Fn 81  CU - Network - End Dos Critical Section                      [D]

   AH = 81h
   AL = critical section number (00h-0Fh) (see #2243)

Notes: normally hooked rather than called
   the handler should reawaken any tasks which were suspended due to an
     attempt to enter the specified critical section
   MS Windows patches the DOS kernel's calls to INT 2A/AH=80h-81h into
     far calls to its own handler, and does not reflect the calls back
     to INT 2A unless SYSTEM.INI contains ReflectDOSInt2A=1 or
     ModifyDOSInt2A=0 in the [386Enh] section

See Also: AH=80h,AH=82h,AX=8700h