C $Header: /home/ubuntu/mnt/e9_copy/MITgcm/eesupp/src/barrier.F,v 1.9 2001/09/21 03:54:34 cnh Exp $ C $Name: $ #include "CPP_EEOPTIONS.h" CBOP C !ROUTINE: BARRIER_INIT C !INTERFACE: SUBROUTINE BARRIER_INIT IMPLICIT NONE C !DESCRIPTION: C *=====================================================================* C | SUBROUTINE BARRIER_INIT C | o Setup global barrier data structures. C *=====================================================================* C | Initialise global barrier data structures that can be used in C | conjunction with MPI or that can also be used to create C *=====================================================================* C !USES: C == Global variables == #include "SIZE.h" #include "EEPARAMS.h" #include "EESUPPORT.h" #include "BARRIER.h" C !LOCAL VARIABLES: C == Local Variables == C I :: Loop counter INTEGER I CEOP DO I=1,nThreads key1(1,I) = INVALID key2(1,I) = INVALID key3(1,I) = INVALID door1 = SHUT door2 = SHUT door3 = SHUT ENDDO RETURN END CBOP C !ROUTINE: BARRIER C !INTERFACE: SUBROUTINE BARRIER( myThid ) IMPLICIT NONE C !DESCRIPTION: C *==========================================================* C | SUBROUTINE BARRIER C | o Barrier routine that uses "busy waiting". C *==========================================================* C | This routine provides a pure fortran mechanism to C | synchronise multiple threads in a multi-threaded code. C | No thread can leave this routine before all the threads C | have entered it. C | Notes C | ===== C | The door and key variables are assumed to have been C | initialized once an initial state of key = INVALID C | and door = SHUT. C | We use the routine FOOL_THE_COMPILER to stop compilers C | generating code which might simply set and test a C | register value. Shared-memory systems only maintain C | coherency over process caches and not registers. C | Also we have to be a bit careful regarding sequential C | consistency - or lack of it. At the moment the code C | assumes a total store order memory model, which some C | machines do not have! However, I have yet to find a C | problem with this I think because the tolerances in C | terms of memory ordering i.e. a little bit of reordering C | probably will not break the barrier mechanism! C | On non-cache coherent systems e.g. T3E we need to use C | a library function to do barriers. C | Note - The PANIC tests can be removed for working code C | I have left them in without an ifdef option C | because without them programming errors can C | lead to infinitely spinning code. If you are C | confident that your code is OK then removing C | them may increase performance. Do not remove these C | lines to make your code "work" If the code is C | stopping in these PANIC blocks then something is C | wrong with your program and it needs to be fixed. C *==========================================================* C !USES: C == Global variables == #include "SIZE.h" #include "EEPARAMS.h" #include "EESUPPORT.h" #include "BARRIER.h" C !INPUT PARAMETERS: C == Routine arguments == INTEGER myThid C !LOCAL VARIABLES: C === Local variables === C nDone :: Counter for number of threads that have C completed a section. C I :: Loop counter INTEGER nDone INTEGER I CEOP CcnhDebugStarts C WRITE(myThid,*) ' Barrier entered ' CcnhDebugEnds C-- Check that thread number is expected range IF ( myThid .LT. 1 .OR. myThid .GT. nThreads ) THEN WRITE(*,*) '!!!!!!! PANIC !!!!!!! CATASTROPHIC ERROR' WRITE(*,*) '!!!!!!! PANIC !!!!!!! in S/R BARRIER myThid = ', & myThid, ' nThreads = ', nThreads STOP 'ABNROMAL END: S/R BARRIER' ENDIF C-- When every threads key1 is valid thread 1 will open door1. IF ( key1(1,myThid) .EQ. VALID ) THEN WRITE(*,*) '!!!!!!! PANIC !!!!!!! CATASTROPHIC ERROR' WRITE(*,*) '!!!!!!! PANIC !!!!!!! in S/R BARRIER myThid = ', & myThid, ' key1 already validated' STOP 'ABNROMAL END: S/R BARRIER' ENDIF key1(1,myThid) = VALID IF ( myThid .eq. 1 ) THEN 10 CONTINUE nDone = 0 DO I=1,nThreads if ( key1(1,I) .EQ. VALID ) nDone = nDone+1 ENDDO CALL FOOL_THE_COMPILER( key1 ) IF ( nDone .LT. nThreads ) GOTO 10 door1 = OPEN ELSE 11 CONTINUE CALL FOOL_THE_COMPILER( door1 ) IF ( door1 .NE. OPEN ) GOTO 11 ENDIF C-- Invalidate keys for door1 here as it is now open key1(1,myThid) = INVALID CcnhDebugStarts C IF ( myThid .EQ. 1 ) THEN C WRITE(*,*) ' DOOR1 Opened ' C ENDIF CcnhDebugEnds C-- I can now shut door3 because I know everyone has reached C-- door1. I can't shut door1 because I don't know if everyone C-- has "gone" through the door yet. Nobody has yet reached C-- door3 because they have to go through door2 first. IF ( myThid .EQ. 1 ) THEN door3 = SHUT ENDIF C-- When every threads key2 is valid thread 1 will open door2. C Notes C ===== C I think that to work with any memory model ( i.e. relaxed, C partial store, total store) the variables key1, key2 and key3 C might need to be set to invalid by thread 1. C IF ( key2(1,myThid) .EQ. VALID ) THEN WRITE(*,*) '!!!!!!! PANIC !!!!!!! CATASTROPHIC ERROR' WRITE(*,*) '!!!!!!! PANIC !!!!!!! in S/R BARRIER myThid = ', & myThid, ' key2 already validated' STOP 'ABNROMAL END: S/R BARRIER' ENDIF key2(1,myThid) = VALID C IF ( myThid .eq. 1 ) THEN 20 CONTINUE nDone = 0 DO I=1,nThreads if ( key2(1,I) .EQ. VALID ) nDone = nDone+1 ENDDO CALL FOOL_THE_COMPILER( key2 ) IF ( nDone .LT. nThreads ) GOTO 20 door2 = OPEN ELSE 21 CONTINUE CALL FOOL_THE_COMPILER( door2 ) IF ( door2 .NE. OPEN ) GOTO 21 ENDIF C-- Invalidate keys for door2 here as it is now open key2(1,myThid) = INVALID C-- I can now shut door1 because I know everyone has reached C-- door2. I can't shut door2 because I don't know if everyone C-- has "gone" through the door yet. Nobody has yet reached C-- door1 because they have to go through door3 first. IF ( myThid .EQ. 1 ) THEN door1 = SHUT ENDIF C-- When every threads key3 is valid thread 1 will open door3. IF ( key3(1,myThid) .EQ. VALID ) THEN WRITE(*,*) '!!!!!!! PANIC !!!!!!! CATASTROPHIC ERROR' WRITE(*,*) '!!!!!!! PANIC !!!!!!! in S/R BARRIER myThid = ', & myThid, ' key3 already validated' STOP 'ABNROMAL END: S/R BARRIER' ENDIF key3(1,myThid) = VALID C IF ( myThid .eq. 1 ) THEN 30 CONTINUE nDone = 0 DO I=1,nThreads if ( key3(1,I) .EQ. VALID ) nDone = nDone+1 ENDDO CALL FOOL_THE_COMPILER( key3 ) IF ( nDone .LT. nThreads ) GOTO 30 door3 = OPEN ELSE 31 CONTINUE CALL FOOL_THE_COMPILER( door3 ) IF ( door3 .NE. OPEN ) GOTO 31 ENDIF C-- Invalidate keys for door3 here as it is now open key3(1,myThid) = INVALID C-- I can now shut door2 because I know everyone has reached C-- door3. I can't shut door3 because I don't know if everyone C-- has "gone" through the door yet. Nobody has yet reached C-- door2 because they have to go through door1 first. IF ( myThid .EQ. 1 ) THEN door2 = SHUT ENDIF CcnhDebugStarts C WRITE(myThid,*) ' Barrier exited ' CcnhDebugEnds RETURN END