add uniqueID initialization (#69)

add the interfaces required to support rocshmem initialization
through the uniqueID mechanism. At the moment this still maps to
MPI initialization underneath the hood, but adding the functions might
simplify the porting of some applications to rocshmem. In addition, if
we need to transition away from MPI one day, this is also one step into
this direction.

src/rocshmem.cpp

@@ -32,7 +32,9 @@
 #include "rocshmem/rocshmem.hpp"
 
 #include <cstdlib>
+#include <cstring>
 #include <functional>
+#include <random>
 
 #include "backend_bc.hpp"
 #include "context_incl.hpp"
@@ -48,6 +50,8 @@
 #include "templates_host.hpp"
 #include "util.hpp"
 
+#include <unistd.h>
+
 namespace rocshmem {
 
 #define VERIFY_BACKEND()                                                      \
@@ -96,14 +100,100 @@ rocshmem_ctx_t ROCSHMEM_HOST_CTX_DEFAULT;
   }
 }
 
+[[maybe_unused]] __host__ int rocshmem_init_attr(unsigned int flags,
+						 rocshmem_init_attr_t *attr) {
+  MPI_Comm comm = MPI_COMM_WORLD;
+
+  if ((attr == nullptr) || 
+      ((flags != ROCSHMEM_INIT_WITH_UNIQUEID) &&
+       (flags != ROCSHMEM_INIT_WITH_MPI_COMM)) ) {
+    fprintf(stderr, "ROCSHMEM_ERROR: %s in file '%s' in line %d\n",
+            "Call 'rocshmem_init_attr: invalid input argument'",
+            __FILE__, __LINE__);
+    return ROCSHMEM_ERROR;
+  }
+
+  if (flags == ROCSHMEM_INIT_WITH_MPI_COMM) {
+    comm = *(static_cast<MPI_Comm*>(attr->mpi_comm));
+  }
+
+  // As of right now, we require initialization through the MPI library.
+  library_init(comm);
+
+  // The unique Id can be used to verify that the processes participating matches
+  // (i.e. they all need to have the same unique Id, as well as the number of ranks.
+  if (flags == ROCSHMEM_INIT_WITH_UNIQUEID) {
+    int worldsize = backend->getNumPEs();
+    if (worldsize != attr->nranks) {
+      fprintf(stderr, "ROCSHMEM_ERROR: %s in file '%s' in line %d\n",
+              "Call 'rocshmem_init_attr: mismatch between world-team size and "
+	      "attribute value'",  __FILE__, __LINE__);
+      // This is a fatal error, a fundamental mismatch between what was requested
+      // and what we have.
+      abort();
+    }
+  }
+
+  return ROCSHMEM_SUCCESS;
+}
+
+[[maybe_unused]] __host__ int rocshmem_set_attr_uniqueid_args(int rank, int nranks,
+							       rocshmem_uniqueid_t *uid,
+							       rocshmem_init_attr_t *attr) {
+  if (uid == nullptr || attr == nullptr) {
+      fprintf(stderr, "ROCSHMEM_ERROR: %s in file '%s' in line %d\n",
+              "Call 'rocshmem_get_uniqueid: invalid input argument'",
+	      __FILE__, __LINE__);
+      return ROCSHMEM_ERROR;
+  }
+
+  attr->rank = rank;
+  attr->nranks = nranks;
+  attr->uid = *uid;
+  attr->mpi_comm = nullptr;
+
+  return ROCSHMEM_SUCCESS;
+}
+
+// Note: this function will be called before rocshmem_init_*, so one
+// cannot assume that a backend is already set
+[[maybe_unused]] __host__ int rocshmem_get_uniqueid(rocshmem_uniqueid_t *uid) {
+  if (uid == nullptr) {
+      fprintf(stderr, "ROCSHMEM_ERROR: %s in file '%s' in line %d\n",
+              "Call 'rocshmem_get_uniqueid: invalid input argument'",
+	      __FILE__, __LINE__);
+      return ROCSHMEM_ERROR;
+  }
+
+  std::random_device dev;
+  std::mt19937_64 rng(dev());
+  std::uniform_int_distribution<uint64_t> dist(0, std::numeric_limits<uint64_t>::max());
+
+  char hostname[HOST_NAME_MAX+1];
+  if (0 != gethostname(hostname, HOST_NAME_MAX)) {
+      fprintf(stderr, "ROCSHMEM_ERROR: %s in file '%s' in line %d\n",
+              "Call 'rocshmem_get_uniqueid: could not get hostname'",
+	      __FILE__, __LINE__);
+      return ROCSHMEM_ERROR;
+  }
+
+  uid->random = dist(rng);
+  std::memcpy(uid->hostname, hostname, ROCSHMEM_HOSTNAME_LEN);
+  uid->pid = static_cast<uint32_t>(getpid());
+
+  return ROCSHMEM_SUCCESS;
+}
+
 [[maybe_unused]] __host__ void rocshmem_init(MPI_Comm comm) {
   library_init(comm);
 }
 
-[[maybe_unused]] __host__ void rocshmem_init_thread(
+[[maybe_unused]] __host__ int rocshmem_init_thread(
     [[maybe_unused]] int required, int *provided, MPI_Comm comm) {
   library_init(comm);
   rocshmem_query_thread(provided);
+
+  return ROCSHMEM_SUCCESS;
 }
 
 [[maybe_unused]] __host__ int rocshmem_my_pe() {