Environmental Inquiries

A set of attributes that describe the execution environment are attached to the communicator MPI_COMM_WORLD when MPI is initialized. MPI_COMM_WORLD The value of these attributes can be inquired by using the function MPI_ATTR_GET described in Chapter . It is erroneous to delete these attributes, free their keys, or change their values.

The list of predefined attribute keys include predefined attributesattribute, predefined

MPI_TAG_UB

Upper bound for tag value. MPI_TAG_UB tag, upper bound

MPI_HOST

Host process rank, if such exists, MPI_HOST host process MPI_PROC_NULL, otherwise. MPI_PROC_NULL

MPI_IO

rank of a node that has regular I/O facilities MPI_IO (possibly rank of calling process). Nodes in the same communicator may return different values for this parameter. I/O inquiry

MPI_WTIME_IS_GLOBAL

Boolean variable that indicates MPI_WTIME_IS_GLOBAL whether clocks are synchronized. clock synchronization

Vendors may add implementation specific parameters (such as node number, real memory size, virtual memory size, etc.)

These predefined attributes do not change value between MPI initialization (MPI_INIT) and MPI completion (MPI_FINALIZE).

 Advice to users. Note that in the C binding, the value 
  returned by these attributes is a pointer to an int containing
  the requested value. (End of advice to users)

• Tag Values
• Host Rank
• I/O Rank
• Clock Synchronization