Debug Tutorial: How to Set Context

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context ( { all | node_list } )
context ( comm_handle : { all | rank_list } )
commshow [ context ] [ expression | data_address ]

A context defines the set of processes to which a command applies.

• Prompt shows default context. It initially contains all nodes on which a program is loaded.

• context command changes the default context.

• Alternatively, a context can be specified for an individual command which overrides the default.

• A TOS application is given a context of host.

• A Cougar application context consists of one or more logical node numbers, all, or a communicator handle and rank list.

• context without arguments prints entire node list.

• commshow without arguments prints list of communicator handles.

• commshow given a MPI_Comm type variable prints its communicator handle.

Example context specifications:

context (host)
context (0)
context (all)
context (0,1)
context (1..20, 25, 30..35)
context (COMMWORLD:all)
context (COMM1:0,5)
context (COMMSELF4:0)
context (ICOMM2:all)

Example communicator handles as displayed by commshow :

In the case below where commshow is given a specific variable to find the handle of, it is normal for an error to be reported for any process which is not contained in that communicator.

(COMMWORLD:all) > commshow
Intracommunicators:
Name        Size    Rank (in COMMWORLD)
=======     =====   ===================
COMMWORLD      6    0..5
COMM1          5    1..5

COMMSELF[0..5]

Intercommunicators:
Name        Intracommunicator Pair
=======     ======================

(COMMWORLD:all) > commshow other
  ***** (COMMWORLD:0) *****

 ** comm3.c{}main(int, char**)#34 other **

ERROR: cannot get communicator information
***    Null pointer argument

  ***** (COMMWORLD:1..5) *****

 ** comm3.c{}main(int, char**)#34 other **
other = COMM1