1 files changed, 69 insertions, 0 deletions
diff --git a/src/H5Fmpi.c b/src/H5Fmpi.c
index ae15142..5434aa5 100644
--- a/src/H5Fmpi.c
+++ b/src/H5Fmpi.c
@@ -287,5 +287,74 @@ H5Fget_mpi_atomicity(hid_t file_id, hbool_t *flag)
 done:
     FUNC_LEAVE_API(ret_value)
 }
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5F_mpi_retrieve_comm
+ *
+ * Purpose:	Retrieves an MPI communicator from the file the location ID 
+ *              is in. If the loc_id is invalid, the fapl_id is used to 
+ *              retrieve the communicator.
+ *
+ * Return:	Success:	Non-negative
+ *
+ * 		Failure:	Negative
+ *
+ * Programmer:	Mohamad Chaarawi
+ *		Feb 14, 2012
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5F_mpi_retrieve_comm(hid_t loc_id, hid_t acspl_id, MPI_Comm *mpi_comm)
+{
+    herr_t    ret_value = SUCCEED;
+
+    FUNC_ENTER_NOAPI(FAIL)
+
+    HDassert(mpi_comm);
+    *mpi_comm = MPI_COMM_NULL;
+
+    /* if the loc_id is valid, then get the comm from the file
+       attached to the loc_id */
+    if(H5I_INVALID_HID != loc_id) {
+        H5G_loc_t loc;
+        H5F_t *f = NULL;
+
+        /* retrieve the file structure */
+        if(H5G_loc(loc_id, &loc) < 0)
+            HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a location")
+        f = loc.oloc->file;
+        HDassert(f);
+
+        /* check if MPIO driver is used */
+        if(H5F_HAS_FEATURE(f, H5FD_FEAT_HAS_MPI)) {
+            /* retrieve the file communicator */
+            if(MPI_COMM_NULL == (*mpi_comm = H5F_mpi_get_comm(f)))
+                HGOTO_ERROR(H5E_VFL, H5E_CANTGET, FAIL, "can't get MPI communicator")
+        }
+    }
+    /* otherwise, this if from H5Fopen or H5Fcreate and has to be collective */
+    else {
+        H5P_genplist_t *plist;      /* Property list pointer */
+
+        HDassert(H5P_isa_class(acspl_id, H5P_FILE_ACCESS));
+
+        if(NULL == (plist = H5P_object_verify(acspl_id, H5P_FILE_ACCESS)))
+            HGOTO_ERROR(H5E_PLIST, H5E_BADTYPE, FAIL, "not a file access list")
+
+        if(H5FD_MPIO == H5P_peek_driver(plist)) {
+            const H5FD_mpio_fapl_t *fa; /* MPIO fapl info */
+
+            if(NULL == (fa = (const H5FD_mpio_fapl_t *)H5P_peek_driver_info(plist)))
+                HGOTO_ERROR(H5E_PLIST, H5E_BADVALUE, FAIL, "bad VFL driver info")
+
+            *mpi_comm = fa->comm;
+        }
+    }
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5F_mpi_retrieve_comm */
+
 #endif /* H5_HAVE_PARALLEL */