statusMPITAG

statusMPITAG refers to the tag field within an MPI_Status object in the Message Passing Interface (MPI). It holds the tag of a received message and is used to identify the kind or purpose of the message when multiple message types may arrive on a single communication channel.

In MPI, receive operations such as MPI_Recv, MPI_Irecv, or MPI_Probe populate a status object with information about the message. After a receive, the tag can be read from status.MPI_TAG in C (or status(MPI_TAG) in Fortran). This value enables applications to differentiate between messages and route them accordingly, especially when using wildcard sources or tags (such as MPI_ANY_TAG).

Practical usage often involves posting a receive with MPI_ANY_TAG and then inspecting the tag value to decide processing, or performing a probe with MPI_Probe to determine the incoming message’s tag before actually receiving. The tag value must fall within the range defined by MPI_TAG_UB, and invalid values may trigger errors. Reserved or special tags (for example, MPI_ANY_TAG) play a role in matching semantics and flow control across processes.

Notes and considerations include language-specific access to the tag field and the interaction between tag values and communicator scope. Understanding statusMPITAG is important for implementing message-driven or event-based patterns in MPI programs, particularly those that must distinguish between multiple message types on shared communicators.

See also: MPI_Status, MPI_TAG_UB, MPI_ANY_TAG, MPI_SOURCE.