C $Header: /u/gcmpack/MITgcm/eesupp/inc/GLOBAL_MAX.h,v 1.5 2009/06/10 03:45:11 jmc Exp $ C $Name: $ CBOP C !ROUTINE: GLOBAL_MAX.h C !INTERFACE: C include "GLOBAL_MAX.h" C !DESCRIPTION: C *==========================================================* C | GLOBAL\_MAX.h C | o Globals used by Fortran global max routine. C *==========================================================* C | The global max shared memory scheme uses global heap data C | structures (.i.e COMMON blocks ). Each thread writes to C | an its own element of the shared memory array and then C | one thread reads all the entries and maxs them. The max C | result is then read by all threads. C | Remember - you are working with regions of memory that C | are being updated concurrently by different threads. C | What happens, when it happens and who gets to see what C | happens at what stage depends on the computer systems C | memory model. Every computer has a different memory model C | and they are never simple. In all current platforms it is C | possible for one thread to see events happening in a C | different order from the order they are written in the C | code. C | Unless you understand this it is not a good idea to C | make modifications te way these header files are setup or C | the way the global max routines work. C *==========================================================* CEOP COMMON / GMAX_COMMON_R8 / phiGMR8 Real*8 phiGMR8(lShare8, 0:MAX_NO_THREADS ) COMMON / GMAX_COMMON_R4 / phiGMR4 Real*4 phiGMR4(lShare4, 0:MAX_NO_THREADS ) COMMON / GMAX_COMMON_I / phiGMI INTEGER phiGMI (lShare4, 0:MAX_NO_THREADS )