[mpich-discuss] Processor hangs on MPI_Comm_accept

[Alberto Giannetti]

Resending with regular file attachments.

I have two simple programs that connect through a MPI_Connect/ 
MPI_Accept scheme.
client.c look for a service published by server.c, connects and  
create an intercomm to send a message, then waits for a message from  
the server and finally disconnects from the intercomm. I run both  
client and server with 2 processors:

mpiexec -n 2 server
mpiexec -n 2 client myfriend

Everything works if I call both MPI_Comm_connect and MPI_Comm_accept  
using the MPI_COMM_SELF group. However, if I use MPI_COMM_WORLD on  
the MPI_Connect() client call, one of the two server processors  
hangs. My trace shows that the client connects to the server, but the  
server never leaves MPI_Comm_accept():

Client trace:
Processor 0 (1463, Sender) initialized
Processor 0 looking for service myfriend-0
Processor 1 (1462, Sender) initialized
Processor 1 looking for service myfriend-1
Processor 0 found port tag#0$port#53996$description#192.168.0.10 
$ifname#192.168.0.10$ looking for service myfriend-0
Processor 0 connecting to 'tag#0$port#53996$description#192.168.0.10 
$ifname#192.168.0.10$'
Processor 1 found port tag#0$port#53995$description#192.168.0.10 
$ifname#192.168.0.10$ looking for service myfriend-1
Processor 1 connecting to 'tag#0$port#53995$description#192.168.0.10 
$ifname#192.168.0.10$'
Processor 1 connected
Processor 1 remote comm size is 1
Processor 1 sending data through intercomm to rank 0...
Processor 0 connected
Processor 0 remote comm size is 1
Processor 0 sending data through intercomm to rank 0...
Processor 1 data sent!
Processor 0 data sent!
Processor 0 received string data 'ciao client' from rank 0, tag 0
Processor 0 disconnecting communicator
Processor 0 finalizing

Server trace:
Processor 0 (1456, Receiver) initialized
Processor 0 opened port tag#0$port#53996$description#192.168.0.10 
$ifname#192.168.0.10$
Publishing port tag#0$port#53996$description#192.168.0.10 
$ifname#192.168.0.10$ as service myfriend-0
Processor 1 (1455, Receiver) initialized
Processor 1 opened port tag#0$port#53995$description#192.168.0.10 
$ifname#192.168.0.10$
Publishing port tag#0$port#53995$description#192.168.0.10 
$ifname#192.168.0.10$ as service myfriend-1
Processor 1 waiting for connections on tag#0$port#53995 
$description#192.168.0.10$ifname#192.168.0.10$, service myfriend-1...
Processor 0 waiting for connections on tag#0$port#53996 
$description#192.168.0.10$ifname#192.168.0.10$, service myfriend-0...
Processor 0 new connection on port tag#0$port#53996 
$description#192.168.0.10$ifname#192.168.0.10$
Processor 0 closing port tag#0$port#53996$description#192.168.0.10 
$ifname#192.168.0.10$
Processor 0 unpublishing service myfriend-0
Processor 0 remote comm size is 2
Processor 0 waiting for data from new intercomm...
Processor 0 got 100 elements from rank 1, tag 1: 0.000000, 1.000000,  
2.000000...
Processor 0 sending string back...
Processor 0 data sent
Processor 0 disconnecting communicator


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