Debug Tutorial: How to Examine Message Queues

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sendqueue [ context ] [ all ]
recvqueue [ context ] [ all ]

Programs doing message passing may have unexpected results or hang because message sends and receives either match unexpectedly or not at all. The ability to view messages and receives sitting in system queues can provide critical information to resolve this kind of programming error.

• sendqueue displays all messages sent to, but not received by, the processes in the context.

• recvqueue displays all unsatisfied receives posted by the processes in the context

• When MPI communicators are used for message passing, the messages displayed are filtered so that only those messages sent within the communicator specified in the context are displayed. Use the all switch to eliminate this additional filter.

• If a posted receive specified a wild card source process or tag, it appears as a -1 for NX messages and ANY for MPI messages.

• If a communicator no longer exists for a message in one of these queues it is displayed with a communicator handle of COMMUNKNOWN and is only seen when the all switch is used.

• Message length is always in bytes, not number of elements.

• Only point-to-point messages are currently included in these displays.

Examples:

(COMMWORLD:all) > sendqueue

 *** Unreceived messages in (COMMWORLD:all)

                                                    Msg Length
      Source          Destination       Msg Tag     (in bytes)
================== ================== ============ ============
(COMMWORLD:0)      (COMMWORLD:1)      22           10          
(COMMWORLD:0)      (COMMWORLD:2)      22           10          
(COMMWORLD:0)      (COMMWORLD:3)      22           10          
(COMMWORLD:0)      (COMMWORLD:4)      22           10          
(COMMWORLD:0)      (COMMWORLD:5)      22           10          
(COMMWORLD:all) > sendqueue -all

 *** Unreceived messages in (COMMWORLD:all)

                                                    Msg Length
      Source          Destination       Msg Tag     (in bytes)
================== ================== ============ ============
(COMMWORLD:0)      (COMMWORLD:1)      22           10          
(COMM1:0)          (COMM1:0)          33           10          
(COMMWORLD:0)      (COMMWORLD:2)      22           10          
(COMM1:0)          (COMM1:1)          33           10          
(COMMWORLD:0)      (COMMWORLD:3)      22           10          
(COMM1:0)          (COMM1:2)          33           10          
(COMMWORLD:0)      (COMMWORLD:4)      22           10          
(COMM1:0)          (COMM1:3)          33           10          
(COMMWORLD:0)      (COMMWORLD:5)      22           10          
(COMM1:0)          (COMM1:4)          33           10          

 *** Unreceived messages in (all)

                                                    Msg Length
      Source          Destination       Msg Type    (in bytes)
================== ================== ============ ============
(COMMWORLD:all) > sendqueue(comm1:all)

 *** Unreceived messages in (COMM1:all)

                                                    Msg Length
      Source          Destination       Msg Tag     (in bytes)
================== ================== ============ ============
(COMM1:0)          (COMM1:0)          33           10          
(COMM1:0)          (COMM1:1)          33           10          
(COMM1:0)          (COMM1:2)          33           10          
(COMM1:0)          (COMM1:3)          33           10          
(COMM1:0)          (COMM1:4)          33           10          
(COMMWORLD:all) > recvqueue

 *** Unsatisfied receives posted in (COMMWORLD:all)

                                                    Msg Length
  Recv Posted By      For Msg From      Msg Tag     (in bytes)
================== ================== ============ ============
(COMMWORLD:all) > recvqueue -all

 *** Unsatisfied receives posted in (COMMWORLD:all)

                                                    Msg Length
  Recv Posted By      For Msg From      Msg Tag     (in bytes)
================== ================== ============ ============
(COMM1:0)          (COMM1:0)          22           10          
(COMM1:1)          (COMM1:0)          22           10          
(COMM1:2)          (COMM1:0)          22           10          
(COMM1:3)          (COMM1:0)          22           10          
(COMM1:4)          (COMM1:0)          22           10          

 *** Unsatisfied receives posted in (all)

                                                    Msg Length
  Recv Posted By      For Msg From      Msg Type    (in bytes)
================== ================== ============ ============
(COMMWORLD:all) > recvqueue(comm1:0)

 *** Unsatisfied receives posted in (COMM1:0)

                                                    Msg Length
  Recv Posted By      For Msg From      Msg Tag     (in bytes)
================== ================== ============ ============
(COMM1:0)          (COMM1:0)          22           10