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C $Header: /u/gcmpack/models/MITgcmUV/eesupp/src/barrier.F,v 1.2 1998/04/23 20:37:29 cnh Exp $ |
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#include "CPP_EEOPTIONS.h" |
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SUBROUTINE BARRIER_INIT |
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#include "EEPARAMS.h" |
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#include "EESUPPORT.h" |
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#include "BARRIER.h" |
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C === Local Variables === |
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INTEGER I |
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DO I=1,nThreads |
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key1(1,I) = INVALID |
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key2(1,I) = INVALID |
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key3(1,I) = INVALID |
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door1 = SHUT |
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door2 = SHUT |
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door3 = SHUT |
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ENDDO |
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RETURN |
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END |
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SUBROUTINE BARRIER( myThid ) |
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IMPLICIT NONE |
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C |
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C /==========================================================\ |
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C | SUBROUTINE BARRIER | |
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C | o Barrier routine that uses "busy waiting". | |
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C |==========================================================| |
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C | This routine provides a pure fortran mechanism to | |
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C | synchronise multiple threads in a multi-threaded code. | |
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C | No thread can leave this routine before all the threads | |
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C | have entered it. | |
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C | Notes | |
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C | ===== | |
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C | The door and key variables are assumed to have been | |
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C | initialized once an initial state of key = INVALID | |
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C | and door = SHUT. | |
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C | We use the routine FOOL_THE_COMPILER to stop compilers | |
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C | generating code which might simply set and test a | |
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C | register value. Shared-memory systems only maintain | |
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C | coherency over process caches and not registers. | |
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C | Also we have to be a bit careful regarding sequential | |
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C | consistency - or lack of it. At the moment the code | |
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C | assumes a total store order memory model, which some | |
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C | machines don't have! However, I have yet to find a | |
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C | problem with this I think because the tolerances in | |
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C | terms of memory ordering i.e. a little bit of reordering | |
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C | probably won't break the barrier mechanism! | |
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C | On non-cache coherent systems e.g. T3E we need to use | |
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C | a library function to do barriers. | |
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C | Note - The PANIC tests can be removed for working code | |
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C | I have left them in without an ifdef option | |
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C | because without them programming errors can | |
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C | lead to infinitely spinning code. If you are | |
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C | confident that your code is OK then removing | |
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C | them may increase performance. Do not remove these| |
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C | lines to make your code "work" If the code is | |
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C | stopping in these PANIC blocks then something is | |
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C | wrong with your program and it needs to be fixed. | |
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C \==========================================================/ |
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#include "EEPARAMS.h" |
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#include "EESUPPORT.h" |
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#include "BARRIER.h" |
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C === Routine arguments === |
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INTEGER myThid |
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C === Local variables === |
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C nDone - Counter for number of threads that have |
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C completed a section. |
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C I - Loop counter |
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INTEGER nDone |
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INTEGER I |
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CcnhDebugStarts |
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cnh |
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C WRITE(myThid,*) ' Barrier entered ' |
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cnh |
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CcnhDebugEnds |
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C-- Check that thread number is expected range |
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IF ( myThid .LT. 1 .OR. myThid .GT. nThreads ) THEN |
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WRITE(0,*) '!!!!!!! PANIC !!!!!!! CATASTROPHIC ERROR' |
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WRITE(0,*) '!!!!!!! PANIC !!!!!!! in S/R BARRIER myThid = ', myThid, ' nThreads = ', nThreads |
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STOP 'ABNROMAL END: S/R BARRIER' |
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ENDIF |
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C-- When every threads key1 is valid thread 1 will open door1. |
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IF ( key1(1,myThid) .EQ. VALID ) THEN |
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WRITE(0,*) '!!!!!!! PANIC !!!!!!! CATASTROPHIC ERROR' |
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WRITE(0,*) '!!!!!!! PANIC !!!!!!! in S/R BARRIER myThid = ', myThid, ' key1 already validated' |
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STOP 'ABNROMAL END: S/R BARRIER' |
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ENDIF |
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key1(1,myThid) = VALID |
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IF ( myThid .eq. 1 ) THEN |
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10 CONTINUE |
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nDone = 0 |
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DO I=1,nThreads |
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if ( key1(1,I) .EQ. VALID ) nDone = nDone+1 |
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ENDDO |
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CALL FOOL_THE_COMPILER( key1 ) |
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IF ( nDone .LT. nThreads ) GOTO 10 |
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door1 = OPEN |
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ELSE |
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11 CONTINUE |
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CALL FOOL_THE_COMPILER( door1 ) |
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IF ( door1 .NE. OPEN ) GOTO 11 |
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ENDIF |
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C-- Invalidate keys for door1 here as it is now open |
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key1(1,myThid) = INVALID |
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CcnhDebugStarts |
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C IF ( myThid .EQ. 1 ) THEN |
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C WRITE(0,*) ' DOOR1 Opened ' |
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C ENDIF |
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CcnhDebugEnds |
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C-- I can now shut door3 because I know everyone has reached |
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C-- door1. I can't shut door1 because I don't know if everyone |
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C-- has "gone" through the door yet. Nobody has yet reached |
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C-- door3 because they have to go through door2 first. |
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IF ( myThid .EQ. 1 ) THEN |
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door3 = SHUT |
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ENDIF |
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C-- When every threads key2 is valid thread 1 will open door2. |
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C Notes |
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C ===== |
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C I don't understand memory ordering and sequential consistency. |
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C I think that to work with any memory model ( i.e. relaxed, |
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C partial store, total store) the variables key1, key2 and key3 |
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C might need to be set to invalid by thread 1. |
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C |
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IF ( key2(1,myThid) .EQ. VALID ) THEN |
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WRITE(0,*) '!!!!!!! PANIC !!!!!!! CATASTROPHIC ERROR' |
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WRITE(0,*) '!!!!!!! PANIC !!!!!!! in S/R BARRIER myThid = ', myThid, ' key2 already validated' |
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STOP 'ABNROMAL END: S/R BARRIER' |
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ENDIF |
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key2(1,myThid) = VALID |
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C |
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IF ( myThid .eq. 1 ) THEN |
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20 CONTINUE |
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nDone = 0 |
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DO I=1,nThreads |
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if ( key2(1,I) .EQ. VALID ) nDone = nDone+1 |
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ENDDO |
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CALL FOOL_THE_COMPILER( key2 ) |
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IF ( nDone .LT. nThreads ) GOTO 20 |
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door2 = OPEN |
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ELSE |
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21 CONTINUE |
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CALL FOOL_THE_COMPILER( door2 ) |
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IF ( door2 .NE. OPEN ) GOTO 21 |
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ENDIF |
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C-- Invalidate keys for door2 here as it is now open |
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key2(1,myThid) = INVALID |
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C-- I can now shut door1 because I know everyone has reached |
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C-- door2. I can't shut door2 because I don't know if everyone |
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C-- has "gone" through the door yet. Nobody has yet reached |
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C-- door1 because they have to go through door3 first. |
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IF ( myThid .EQ. 1 ) THEN |
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door1 = SHUT |
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ENDIF |
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C-- When every threads key3 is valid thread 1 will open door3. |
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IF ( key3(1,myThid) .EQ. VALID ) THEN |
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WRITE(0,*) '!!!!!!! PANIC !!!!!!! CATASTROPHIC ERROR' |
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WRITE(0,*) '!!!!!!! PANIC !!!!!!! in S/R BARRIER myThid = ', myThid, ' key3 already validated' |
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STOP 'ABNROMAL END: S/R BARRIER' |
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ENDIF |
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key3(1,myThid) = VALID |
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C |
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IF ( myThid .eq. 1 ) THEN |
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30 CONTINUE |
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nDone = 0 |
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DO I=1,nThreads |
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if ( key3(1,I) .EQ. VALID ) nDone = nDone+1 |
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ENDDO |
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CALL FOOL_THE_COMPILER( key3 ) |
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IF ( nDone .LT. nThreads ) GOTO 30 |
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door3 = OPEN |
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ELSE |
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31 CONTINUE |
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CALL FOOL_THE_COMPILER( door3 ) |
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IF ( door3 .NE. OPEN ) GOTO 31 |
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ENDIF |
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C-- Invalidate keys for door3 here as it is now open |
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key3(1,myThid) = INVALID |
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C-- I can now shut door2 because I know everyone has reached |
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C-- door3. I can't shut door3 because I don't know if everyone |
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C-- has "gone" through the door yet. Nobody has yet reached |
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C-- door2 because they have to go through door1 first. |
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IF ( myThid .EQ. 1 ) THEN |
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door2 = SHUT |
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ENDIF |
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CcnhDebugStarts |
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cnh |
1.3 |
C WRITE(myThid,*) ' Barrier exited ' |
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cnh |
1.1 |
CcnhDebugEnds |
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RETURN |
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END |
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