From ea410132c54a8b71a8a980a1aea59c758388859f Mon Sep 17 00:00:00 2001
From: Lars Hoffmann <l.hoffmann@fz-juelich.de>
Date: Fri, 19 Jul 2024 07:58:44 +0200
Subject: [PATCH] Update MPI broadcasting code.

---
 src/mptrac.c | 29 ++++++++++++++---------------
 src/mptrac.h | 28 ++++++++++++++++++----------
 2 files changed, 32 insertions(+), 25 deletions(-)

diff --git a/src/mptrac.c b/src/mptrac.c
index 73f9b1339..db6b6133a 100644
--- a/src/mptrac.c
+++ b/src/mptrac.c
@@ -42,30 +42,29 @@ static curandGenerator_t rng_curand;
 /*****************************************************************************/
 
 #ifdef MPI
-void broadcast_large_data(void* data, size_t N, int root, MPI_Comm comm) {
-  
+void broadcast_large_data(
+  void *data,
+  size_t N) {
+
 #define CHUNK_SIZE 2147483647
-  
-  /* Get rank... */
-  int rank;
-  MPI_Comm_rank(comm, &rank);
-  
+
   /* Broadcast the size of the data first... */
-  MPI_Bcast(&N, 1, MPI_UINT64_T, root, comm);
-  
+  MPI_Bcast(&N, 1, MPI_UINT64_T, 0, MPI_COMM_WORLD);
+
   /* Calculate the number of chunks... */
   size_t num_chunks = (N + CHUNK_SIZE - 1) / CHUNK_SIZE;
-  
+
   /* Loop over chunks... */
   for (size_t i = 0; i < num_chunks; i++) {
-    
+
     /* Determine the start and end indices for the current chunk... */
     size_t start = i * CHUNK_SIZE;
     size_t end = (start + CHUNK_SIZE > N) ? N : start + CHUNK_SIZE;
     size_t chunk_size = end - start;
-    
+
     /* Broadcast the current chunk... */
-    MPI_Bcast((char*)data + start, (int)chunk_size, MPI_BYTE, root, comm);
+    MPI_Bcast((char *) data + start, (int) chunk_size, MPI_BYTE, 0,
+	      MPI_COMM_WORLD);
   }
 }
 #endif
@@ -5803,10 +5802,10 @@ int read_met(
     LOG(2, "Broadcast data on rank %d...", rank);
 
     /* Broadcast... */
-    broadcast_large_data(met, sizeof(met_t), 0, MPI_COMM_WORLD);
+    broadcast_large_data(met, sizeof(met_t));
   }
 #endif
-  
+
   /* Return success... */
   return 1;
 }
diff --git a/src/mptrac.h b/src/mptrac.h
index 338421cc9..2e430478a 100644
--- a/src/mptrac.h
+++ b/src/mptrac.h
@@ -3421,22 +3421,30 @@ typedef struct {
    Functions...
    ------------------------------------------------------------ */
 
-#ifdef MPI
 /**
- * @brief Broadcasts large data in chunks from the root process to all other processes in the given communicator.
+ * @brief Broadcasts large data across all processes in an MPI communicator.
+ *
+ * This function divides the data into manageable chunks and broadcasts each
+ * chunk sequentially. This approach is necessary because the data size may
+ * exceed the maximum allowable message size for a single MPI_Bcast operation.
  *
- * This function splits the data into manageable chunks (up to 2 GB - 1 byte each) and broadcasts each chunk sequentially.
- * This approach avoids issues with broadcasting very large data sizes that exceed the limits of a single MPI_Bcast call.
+ * @param data Pointer to the data to be broadcasted.
+ * @param N    Size of the data in bytes.
  *
- * @param data Pointer to the data to be broadcast. This pointer should point to a contiguous block of memory.
- * @param N The size of the data in bytes.
- * @param root The rank of the root process that holds the initial data.
- * @param comm The MPI communicator.
+ * The function first broadcasts the total size of the data to all processes.
+ * Then, it calculates the number of chunks needed to broadcast the entire data.
+ * Each chunk is broadcasted in sequence until the entire data has been sent.
+ * 
+ * The maximum chunk size is defined as CHUNK_SIZE (2147483647 bytes).
+ *
+ * @note The function assumes that the MPI environment has been initialized 
+ * before calling this function and will be finalized afterward.
  *
  * @author Lars Hoffmann
  */
-void broadcast_large_data(void* data, size_t N, int root, MPI_Comm comm);
-#endif
+void broadcast_large_data(
+  void *data,
+  size_t N);
 
 /**
  * @brief Converts Cartesian coordinates to geographic coordinates.