Keep temporary Isend views alive

README.md

@@ -1,5 +1,5 @@
 # kokkos-comm
-MPI Wrapper for [Kokkos](https://github.com/kokkos/kokkos).
+A toy MPI wrapper for [Kokkos](https://github.com/kokkos/kokkos).
 
 ```
 mkdir -p build && cd build
@@ -8,6 +8,11 @@ make
 ctest
 ```
 
+## Design
+
+- [x] use `Kokkos::deep_copy` to handle packing and unpacking of non-contiguous views
+  - When non-contiguous views are passed to an MPI function, a temporary contiguous view of matching extent is allocated, and `Kokkos::deep_copy` is used to pack the data.
+
 
 ## Considerations
 

src/KokkosComm_request.hpp

@@ -1,19 +1,48 @@
 #pragma once
 
+#include <memory>
+
 #include <mpi.h>
 
 namespace KokkosComm {
 
+
+
+
+
 class Req {
+private:
+
+  // a type-erased view. Request uses these to keep temporary views alive for the lifetime of "Immediate" MPI operations
+  struct ViewHolderBase {
+    virtual ~ViewHolderBase(){}
+  };
+  template <typename V>
+  struct ViewHolder : ViewHolderBase {
+    ViewHolder(const V &v) : v_(v) {}
+    V v_;
+  };
+
 public:
   Req() : req_(MPI_REQUEST_NULL) {}
 
   MPI_Request &mpi_req() { return req_; }
 
-  void wait() { MPI_Wait(&req_, MPI_STATUS_IGNORE); }
+  void wait() { 
+    MPI_Wait(&req_, MPI_STATUS_IGNORE);
+    until_waits_.clear(); // drop any views we're keeping alive until wait()
+  }
+
+  // keep a reference to this view around until wait() is called
+  template <typename View>
+  void keep_until_wait(const View &v) {
+    until_waits_.push_back(std::make_shared<ViewHolder<View>>(v));
+  }
 
 private:
   MPI_Request req_;
+
+  std::vector<std::shared_ptr<ViewHolderBase>> until_waits_;
 };
 
 } // namespace KokkosComm

src/impl/KokkosComm_isend.hpp

@@ -30,6 +30,7 @@ KokkosComm::Req isend(const ExecSpace &space, const SendView &sv, int dest,
       space.fence();
       MPI_Isend(packed.data(), packed.span() * sizeof(value_type), MPI_PACKED,
                 dest, tag, comm, &req.mpi_req());
+      req.keep_until_wait(packed);
       return req;
     } else {
       static_assert(std::is_void_v<SendView>,