如何在Open MPI 3.0.0的MPI_Wait包装器中区分收发请求？

Great question! The standard MPI API doesn't expose a direct way to check if an MPI_Request is tied to a send or receive operation—but since you're working with Open MPI 3.0.0, you can leverage the implementation's internal structures to get this information. Here's how to do it:

Key Background #

Open MPI stores all request metadata in an internal struct called ompi_request_t. This struct includes a req_type field that identifies the type of operation the request corresponds to. Send requests use the constant OMPI_REQUEST_SEND, while receive requests use OMPI_REQUEST_RECV.

Modified Wrapper Code #

First, include Open MPI's internal request header to access these definitions. Then cast the MPI_Request to the internal struct type and check the req_type field:

/* ================== C Wrappers for MPI_Wait ================== */
#include <stdio.h>
#include <ompi/request/request.h> // Required for Open MPI's request internals

_EXTERN_C_ int PMPI_Wait(MPI_Request *request, MPI_Status *status);
_EXTERN_C_ int MPI_Wait(MPI_Request *request, MPI_Status *status) {
    int _wrap_py_return_val = 0;

    // Guard against null requests to avoid crashes
    if (*request == MPI_REQUEST_NULL) {
        _wrap_py_return_val = PMPI_Wait(request, status);
        return _wrap_py_return_val;
    }

    // Cast the standard MPI_Request to Open MPI's internal request struct
    ompi_request_t *ompi_req = (ompi_request_t *)*request;

    // Check if it's a send or receive request
    if (ompi_req->req_type == OMPI_REQUEST_SEND) {
        printf("send\n");
    } else if (ompi_req->req_type == OMPI_REQUEST_RECV) {
        printf("recv\n");
    } else {
        // Handle other request types (e.g., collective operations) if needed
        printf("other request type\n");
    }

    _wrap_py_return_val = PMPI_Wait(request, status);
    return _wrap_py_return_val;
}

Important Notes #

• Non-portability: This approach is specific to Open MPI 3.0.0. Internal structures and constants can change between Open MPI versions, and this won't work with other MPI implementations like MPICH.
• Compilation: When building your wrapper, ensure the compiler can find Open MPI's internal headers. Use mpicc with the include path from ompi_info --path sysincludedir, e.g.:

  mpicc -I$(ompi_info --path sysincludedir) your_wrapper.c -o your_wrapper
  

• Request Validity: Always check for MPI_REQUEST_NULL before casting to avoid segmentation faults, as shown in the code above.

内容的提问来源于stack exchange，提问作者JACK M