MPIIprobe

MPI_Iprobe is a nonblocking probe operation in the Message Passing Interface (MPI) standard. It checks for the presence of an incoming message without blocking the calling process, allowing the program to decide how to proceed based on whether a message has arrived.

The typical C declaration is int MPI_Iprobe(int source, int tag, MPI_Comm comm, int *flag, MPI_Status *status). The parameters source and tag specify the message’s origin and label, while comm designates the communicator. The flag is set to true if a matching message is available, and status contains information about that message. If no message is available, flag is false and the contents of status are undefined. MPI_Iprobe can be used with specific values of source and tag or with MPI_ANY_SOURCE and/or MPI_ANY_TAG to check for messages from any source or with any tag.

MPI_Iprobe does not receive the message; it merely indicates whether a suitable message is ready to be received. If flag is true, a subsequent MPI_Recv or MPI_Irecv can be posted to actually transfer the data. The status object can then be used to obtain details such as the actual source and tag of the message. In many patterns, MPI_Iprobe is used to implement asynchronous or event-driven communication, often together with a postposted receive.

Compared with MPI_Probe, MPI_Iprobe is nonblocking: it returns immediately, allowing the program to perform other work or periodically poll for messages. This facility is central to avoiding deadlock in certain communication scenarios and to building responsive parallel applications.