MPIWait

MPI_Wait is a blocking routine in the Message Passing Interface (MPI) used to wait for the completion of a single non-blocking operation. It takes a pointer to an MPI_Request and an MPI_Status, and returns when the referenced operation has completed.

The request argument is typically obtained from non-blocking calls such as MPI_Isend or MPI_Irecv, or from persistent requests created with operations like MPI_Send_init or MPI_Recv_init and started with MPI_Start. The status argument receives information about the completed operation, including the source, tag, and possibly the amount of data transferred. If the status is not needed, MPI_STATUS_IGNORE can be passed.

After MPI_Wait completes, the behavior of the request handle depends on the type of request. For ordinary (non-persistent) requests, the handle becomes MPI_REQUEST_NULL. For persistent requests, the handle remains valid and can be reused by a subsequent MPI_Start or MPI_Startall; the request may be freed with MPI_Request_free when no longer needed.

MPI_Wait is commonly used to synchronize a computation with a non-blocking communication operation, enabling overlap of computation and communication. It blocks the calling process until the specified operation finishes, ensuring that subsequent code operates on data that has already been transferred.

Return values indicate success or error. The function returns MPI_SUCCESS on success; on error, an MPI error code is returned and the MPI error handler may be invoked (default behavior may abort the program unless configured otherwise). Related routines include MPI_Test (non-blocking check), MPI_Waitall, and MPI_Waitany.