| 1 |
C $Header: /u/gcmpack/models/MITgcmUV/eesupp/src/barrier.F,v 1.3 1998/06/10 17:05:59 cnh Exp $ |
| 2 |
|
| 3 |
#include "CPP_EEOPTIONS.h" |
| 4 |
|
| 5 |
SUBROUTINE BARRIER_INIT |
| 6 |
|
| 7 |
#include "SIZE.h" |
| 8 |
#include "EEPARAMS.h" |
| 9 |
#include "EESUPPORT.h" |
| 10 |
#include "BARRIER.h" |
| 11 |
|
| 12 |
C === Local Variables === |
| 13 |
INTEGER I |
| 14 |
|
| 15 |
DO I=1,nThreads |
| 16 |
key1(1,I) = INVALID |
| 17 |
key2(1,I) = INVALID |
| 18 |
key3(1,I) = INVALID |
| 19 |
door1 = SHUT |
| 20 |
door2 = SHUT |
| 21 |
door3 = SHUT |
| 22 |
ENDDO |
| 23 |
|
| 24 |
RETURN |
| 25 |
END |
| 26 |
SUBROUTINE BARRIER( myThid ) |
| 27 |
IMPLICIT NONE |
| 28 |
C |
| 29 |
C /==========================================================\ |
| 30 |
C | SUBROUTINE BARRIER | |
| 31 |
C | o Barrier routine that uses "busy waiting". | |
| 32 |
C |==========================================================| |
| 33 |
C | This routine provides a pure fortran mechanism to | |
| 34 |
C | synchronise multiple threads in a multi-threaded code. | |
| 35 |
C | No thread can leave this routine before all the threads | |
| 36 |
C | have entered it. | |
| 37 |
C | Notes | |
| 38 |
C | ===== | |
| 39 |
C | The door and key variables are assumed to have been | |
| 40 |
C | initialized once an initial state of key = INVALID | |
| 41 |
C | and door = SHUT. | |
| 42 |
C | We use the routine FOOL_THE_COMPILER to stop compilers | |
| 43 |
C | generating code which might simply set and test a | |
| 44 |
C | register value. Shared-memory systems only maintain | |
| 45 |
C | coherency over process caches and not registers. | |
| 46 |
C | Also we have to be a bit careful regarding sequential | |
| 47 |
C | consistency - or lack of it. At the moment the code | |
| 48 |
C | assumes a total store order memory model, which some | |
| 49 |
C | machines don't have! However, I have yet to find a | |
| 50 |
C | problem with this I think because the tolerances in | |
| 51 |
C | terms of memory ordering i.e. a little bit of reordering | |
| 52 |
C | probably won't break the barrier mechanism! | |
| 53 |
C | On non-cache coherent systems e.g. T3E we need to use | |
| 54 |
C | a library function to do barriers. | |
| 55 |
C | Note - The PANIC tests can be removed for working code | |
| 56 |
C | I have left them in without an ifdef option | |
| 57 |
C | because without them programming errors can | |
| 58 |
C | lead to infinitely spinning code. If you are | |
| 59 |
C | confident that your code is OK then removing | |
| 60 |
C | them may increase performance. Do not remove these| |
| 61 |
C | lines to make your code "work" If the code is | |
| 62 |
C | stopping in these PANIC blocks then something is | |
| 63 |
C | wrong with your program and it needs to be fixed. | |
| 64 |
C \==========================================================/ |
| 65 |
|
| 66 |
#include "SIZE.h" |
| 67 |
#include "EEPARAMS.h" |
| 68 |
#include "EESUPPORT.h" |
| 69 |
#include "BARRIER.h" |
| 70 |
|
| 71 |
C === Routine arguments === |
| 72 |
INTEGER myThid |
| 73 |
|
| 74 |
C === Local variables === |
| 75 |
C nDone - Counter for number of threads that have |
| 76 |
C completed a section. |
| 77 |
C I - Loop counter |
| 78 |
INTEGER nDone |
| 79 |
INTEGER I |
| 80 |
|
| 81 |
CcnhDebugStarts |
| 82 |
C WRITE(myThid,*) ' Barrier entered ' |
| 83 |
CcnhDebugEnds |
| 84 |
|
| 85 |
C-- Check that thread number is expected range |
| 86 |
IF ( myThid .LT. 1 .OR. myThid .GT. nThreads ) THEN |
| 87 |
WRITE(0,*) '!!!!!!! PANIC !!!!!!! CATASTROPHIC ERROR' |
| 88 |
WRITE(0,*) '!!!!!!! PANIC !!!!!!! in S/R BARRIER myThid = ', myThid, ' nThreads = ', nThreads |
| 89 |
STOP 'ABNROMAL END: S/R BARRIER' |
| 90 |
ENDIF |
| 91 |
|
| 92 |
C-- When every threads key1 is valid thread 1 will open door1. |
| 93 |
IF ( key1(1,myThid) .EQ. VALID ) THEN |
| 94 |
WRITE(0,*) '!!!!!!! PANIC !!!!!!! CATASTROPHIC ERROR' |
| 95 |
WRITE(0,*) '!!!!!!! PANIC !!!!!!! in S/R BARRIER myThid = ', myThid, ' key1 already validated' |
| 96 |
STOP 'ABNROMAL END: S/R BARRIER' |
| 97 |
ENDIF |
| 98 |
key1(1,myThid) = VALID |
| 99 |
|
| 100 |
IF ( myThid .eq. 1 ) THEN |
| 101 |
10 CONTINUE |
| 102 |
nDone = 0 |
| 103 |
DO I=1,nThreads |
| 104 |
if ( key1(1,I) .EQ. VALID ) nDone = nDone+1 |
| 105 |
ENDDO |
| 106 |
CALL FOOL_THE_COMPILER( key1 ) |
| 107 |
IF ( nDone .LT. nThreads ) GOTO 10 |
| 108 |
door1 = OPEN |
| 109 |
ELSE |
| 110 |
11 CONTINUE |
| 111 |
CALL FOOL_THE_COMPILER( door1 ) |
| 112 |
IF ( door1 .NE. OPEN ) GOTO 11 |
| 113 |
ENDIF |
| 114 |
C-- Invalidate keys for door1 here as it is now open |
| 115 |
key1(1,myThid) = INVALID |
| 116 |
|
| 117 |
CcnhDebugStarts |
| 118 |
C IF ( myThid .EQ. 1 ) THEN |
| 119 |
C WRITE(0,*) ' DOOR1 Opened ' |
| 120 |
C ENDIF |
| 121 |
CcnhDebugEnds |
| 122 |
|
| 123 |
C-- I can now shut door3 because I know everyone has reached |
| 124 |
C-- door1. I can't shut door1 because I don't know if everyone |
| 125 |
C-- has "gone" through the door yet. Nobody has yet reached |
| 126 |
C-- door3 because they have to go through door2 first. |
| 127 |
IF ( myThid .EQ. 1 ) THEN |
| 128 |
door3 = SHUT |
| 129 |
ENDIF |
| 130 |
|
| 131 |
C-- When every threads key2 is valid thread 1 will open door2. |
| 132 |
C Notes |
| 133 |
C ===== |
| 134 |
C I don't understand memory ordering and sequential consistency. |
| 135 |
C I think that to work with any memory model ( i.e. relaxed, |
| 136 |
C partial store, total store) the variables key1, key2 and key3 |
| 137 |
C might need to be set to invalid by thread 1. |
| 138 |
C |
| 139 |
IF ( key2(1,myThid) .EQ. VALID ) THEN |
| 140 |
WRITE(0,*) '!!!!!!! PANIC !!!!!!! CATASTROPHIC ERROR' |
| 141 |
WRITE(0,*) '!!!!!!! PANIC !!!!!!! in S/R BARRIER myThid = ', myThid, ' key2 already validated' |
| 142 |
STOP 'ABNROMAL END: S/R BARRIER' |
| 143 |
ENDIF |
| 144 |
key2(1,myThid) = VALID |
| 145 |
C |
| 146 |
IF ( myThid .eq. 1 ) THEN |
| 147 |
20 CONTINUE |
| 148 |
nDone = 0 |
| 149 |
DO I=1,nThreads |
| 150 |
if ( key2(1,I) .EQ. VALID ) nDone = nDone+1 |
| 151 |
ENDDO |
| 152 |
CALL FOOL_THE_COMPILER( key2 ) |
| 153 |
IF ( nDone .LT. nThreads ) GOTO 20 |
| 154 |
door2 = OPEN |
| 155 |
ELSE |
| 156 |
21 CONTINUE |
| 157 |
CALL FOOL_THE_COMPILER( door2 ) |
| 158 |
IF ( door2 .NE. OPEN ) GOTO 21 |
| 159 |
ENDIF |
| 160 |
|
| 161 |
C-- Invalidate keys for door2 here as it is now open |
| 162 |
key2(1,myThid) = INVALID |
| 163 |
|
| 164 |
C-- I can now shut door1 because I know everyone has reached |
| 165 |
C-- door2. I can't shut door2 because I don't know if everyone |
| 166 |
C-- has "gone" through the door yet. Nobody has yet reached |
| 167 |
C-- door1 because they have to go through door3 first. |
| 168 |
IF ( myThid .EQ. 1 ) THEN |
| 169 |
door1 = SHUT |
| 170 |
ENDIF |
| 171 |
|
| 172 |
|
| 173 |
C-- When every threads key3 is valid thread 1 will open door3. |
| 174 |
IF ( key3(1,myThid) .EQ. VALID ) THEN |
| 175 |
WRITE(0,*) '!!!!!!! PANIC !!!!!!! CATASTROPHIC ERROR' |
| 176 |
WRITE(0,*) '!!!!!!! PANIC !!!!!!! in S/R BARRIER myThid = ', myThid, ' key3 already validated' |
| 177 |
STOP 'ABNROMAL END: S/R BARRIER' |
| 178 |
ENDIF |
| 179 |
key3(1,myThid) = VALID |
| 180 |
C |
| 181 |
IF ( myThid .eq. 1 ) THEN |
| 182 |
30 CONTINUE |
| 183 |
nDone = 0 |
| 184 |
DO I=1,nThreads |
| 185 |
if ( key3(1,I) .EQ. VALID ) nDone = nDone+1 |
| 186 |
ENDDO |
| 187 |
CALL FOOL_THE_COMPILER( key3 ) |
| 188 |
IF ( nDone .LT. nThreads ) GOTO 30 |
| 189 |
door3 = OPEN |
| 190 |
ELSE |
| 191 |
31 CONTINUE |
| 192 |
CALL FOOL_THE_COMPILER( door3 ) |
| 193 |
IF ( door3 .NE. OPEN ) GOTO 31 |
| 194 |
ENDIF |
| 195 |
|
| 196 |
C-- Invalidate keys for door3 here as it is now open |
| 197 |
key3(1,myThid) = INVALID |
| 198 |
|
| 199 |
C-- I can now shut door2 because I know everyone has reached |
| 200 |
C-- door3. I can't shut door3 because I don't know if everyone |
| 201 |
C-- has "gone" through the door yet. Nobody has yet reached |
| 202 |
C-- door2 because they have to go through door1 first. |
| 203 |
IF ( myThid .EQ. 1 ) THEN |
| 204 |
door2 = SHUT |
| 205 |
ENDIF |
| 206 |
|
| 207 |
CcnhDebugStarts |
| 208 |
C WRITE(myThid,*) ' Barrier exited ' |
| 209 |
CcnhDebugEnds |
| 210 |
|
| 211 |
RETURN |
| 212 |
END |
Parent Directory
| 
Revision Log
| 
Revision Graph