Sending, receiving result in deadlock

[anishtain4]

I'm trying to solve a simple problem with MPI but when I comment all the PRINT lines the program gets into a deadlock, when I uncomment one of them then the programm proceeds smoothly!!!! I can't understand what is wrong with this? I'm using blocking send and receive so time difference that print makes should not has any effect on the overal performance!
The idea of IF is that odd processes first send and evens recieve then vice versa, so there should not be any deadlock even if there don't be any buffer on the way!
What is wrong with my algorithm that makes it break?

[bash] integer,parameter   ::IM=100,JM=100  
 REAL,ALLOCATABLE  ::T(:,:),TF(:,:)  
 ..  
  CALL MPI_COMM_RANK(MPI_COMM_WORLD,RNK,IERR)  
  CALL MPI_COMM_SIZE(MPI_COMM_WORLD,SIZ,IERR)  
 ..  
 prv = rnk-1  
 nxt = rnk+1  
 LIM = INT(IM/SIZ)  
 IF (rnk==0) THEN  
     ALLOCATE(TF(IM,JM))  
     prv = MPI_PROC_NULL  
 ELSEIF(rnk==siz-1) THEN  
     NXT = MPI_PROC_NULL  
     LIM = LIM+MOD(IM,SIZ)  
 END IF  
 ALLOCATE(T(LIM+2,JM+2))  
   
 IF (MOD(RNK,2)==0) THEN  
         CALL MPI_SEND(T(2,:),JM+2,MPI_REAL,PRV,10,MPI_COMM_WORLD,IERR)  
         !PRINT*,RNK,'SENT'  
         CALL MPI_RECV(T(1,:),JM+2,MPI_REAL,PRV,20,MPI_COMM_WORLD,STAT,IERR)  
         !PRINT*,RNK,'RECIEVED'  
     ELSE  
         CALL MPI_RECV(T(LIM+2,:),JM+2,MPI_REAL,NXT,10,MPI_COMM_WORLD,STAT,IERR)  
         PRINT*,RNK,'RECIEVED'  
        CALL MPI_SEND(T(LIM+1,:),JM+2,MPI_REAL,NXT,20,MPI_COMM_WORLD,IERR)  
         !PRINT*,RNK,'SENT'  
     END IF [/bash]

[Dmitry_K_Intel2]

Hi Anishtain,

Your code (a bit modified) below works fine for number of processes from 2 to 16 on Intel64.
Do you define all variables? SIZ may be a real variable.

implicit none
include 'mpif.h'

integer,parameter :: IM=100,JM=100
REAL,ALLOCATABLE :: T(:,:),TF(:,:)
integer RNK,IERR,SIZ, prv, nxt, LIM
integer STAT(MPI_STATUS_SIZE)

CALL MPI_INIT(IERR)

CALL MPI_COMM_RANK(MPI_COMM_WORLD,RNK,IERR)
CALL MPI_COMM_SIZE(MPI_COMM_WORLD,SIZ,IERR)

prv = rnk-1
nxt = rnk+1

LIM = INT(IM/SIZ)

IF (rnk==0) THEN
ALLOCATE(TF(IM,JM))
prv = MPI_PROC_NULL

ELSEIF(rnk==siz-1) THEN
NXT = MPI_PROC_NULL
LIM = LIM+MOD(IM,SIZ)

END IF

ALLOCATE(T(LIM+2,JM+2))

IF (MOD(RNK,2)==0) THEN
CALL MPI_SEND(T(2,:),JM+2,MPI_REAL,PRV,10,MPI_COMM_WORLD,IERR)
!PRINT*,RNK,'SENT'
CALL MPI_RECV(T(1,:),JM+2,MPI_REAL,PRV,20,MPI_COMM_WORLD,STAT,IERR)
!PRINT*,RNK,'RECIEVED'
ELSE
CALL MPI_RECV(T(LIM+2,:),JM+2,MPI_REAL,NXT,10,MPI_COMM_WORLD,STAT,IERR)
!PRINT*,RNK,'RECIEVED'
CALL MPI_SEND(T(LIM+1,:),JM+2,MPI_REAL,NXT,20,MPI_COMM_WORLD,IERR)
!PRINT*,RNK,'SENT'
END IF

IF (rnk==0) DEALLOCATE(TF)

DEALLOCATE(T)

call MPI_FINALIZE(IERR)

print *, rnk, " - done"

END PROGRAM


Regards!
Dmitry

[anishtain4]

Thanks Dmitry, the problem was with the optimization as I found by someone's advice. I just added the -O0 and it works. siz was integer btw.