Fix problems with vlens and refs inside compound using H5VLget_file_type() (#274)hdf5-1_13_0-rc5

* Fixed problems with vlens and refs inside compound using H5VLget_file_type()

* Fix date in RELEASE.txt

* Add assertions

* Move some manipulation of H5VL_object_t struct fields into the H5VL
package.

13 files changed, 151 insertions, 36 deletions

diff --git a/release_docs/RELEASE.txt b/release_docs/RELEASE.txt
index 3bd3e01..404c944 100644
--- a/release_docs/RELEASE.txt
+++ b/release_docs/RELEASE.txt
@@ -669,6 +669,15 @@ Bug Fixes since HDF5-1.12.0 release
 ==================================
     Library
     -------
+    - Fixed problems with vlens and refs inside compound using
+      H5VLget_file_type()
+
+        Modified library to properly ref count H5VL_object_t structs and only
+        consider file vlen and reference types to be equal if their files are
+        the same.
+
+        (NAF - 2021/01/22)
+
     - Creation of dataset with optional filter
 
         When the combination of type, space, etc doesn't work for filter
diff --git a/src/H5Odtype.c b/src/H5Odtype.c
index b6e986d..c1effad 100644
--- a/src/H5Odtype.c
+++ b/src/H5Odtype.c
@@ -579,8 +579,10 @@ H5O__dtype_decode_helper(unsigned *ioflags /*in,out*/, const uint8_t **pp, H5T_t
 done:
     if (ret_value < 0)
         if (dt != NULL) {
-            if (dt->shared != NULL)
+            if (dt->shared != NULL) {
+                HDassert(!dt->shared->owned_vol_obj);
                 dt->shared = H5FL_FREE(H5T_shared_t, dt->shared);
+            } /* end if */
             dt = H5FL_FREE(H5T_t, dt);
         } /* end if */
 
diff --git a/src/H5T.c b/src/H5T.c
index 59f0224..33a75c9 100644
--- a/src/H5T.c
+++ b/src/H5T.c
@@ -1479,6 +1479,8 @@ done:
             if (copied_dtype)
                 (void)H5T_close_real(dt);
             else {
+                if (dt->shared->owned_vol_obj && H5VL_free_object(dt->shared->owned_vol_obj) < 0)
+                    HDONE_ERROR(H5E_DATATYPE, H5E_CANTCLOSEOBJ, FAIL, "unable to close owned VOL object")
                 dt->shared = H5FL_FREE(H5T_shared_t, dt->shared);
                 dt         = H5FL_FREE(H5T_t, dt);
             } /* end else */
@@ -3447,6 +3449,8 @@ H5T__create(H5T_class_t type, size_t size)
 done:
     if (NULL == ret_value) {
         if (dt) {
+            if (dt->shared->owned_vol_obj && H5VL_free_object(dt->shared->owned_vol_obj) < 0)
+                HDONE_ERROR(H5E_DATATYPE, H5E_CANTCLOSEOBJ, NULL, "unable to close owned VOL object")
             dt->shared = H5FL_FREE(H5T_shared_t, dt->shared);
             dt         = H5FL_FREE(H5T_t, dt);
         }
@@ -3489,9 +3493,12 @@ H5T__initiate_copy(const H5T_t *old_dt)
     /* Copy shared information */
     *(new_dt->shared) = *(old_dt->shared);
 
-    /* Reset VOL fields */
+    /* Increment ref count on owned VOL object */
+    if (new_dt->shared->owned_vol_obj)
+        (void)H5VL_object_inc_rc(new_dt->shared->owned_vol_obj);
+
+    /* Reset vol_obj field */
     new_dt->vol_obj               = NULL;
-    new_dt->shared->owned_vol_obj = NULL;
 
     /* Set return value */
     ret_value = new_dt;
@@ -3499,8 +3506,11 @@ H5T__initiate_copy(const H5T_t *old_dt)
 done:
     if (ret_value == NULL)
         if (new_dt) {
-            if (new_dt->shared)
+            if (new_dt->shared) {
+                if (new_dt->shared->owned_vol_obj && H5VL_free_object(new_dt->shared->owned_vol_obj) < 0)
+                    HDONE_ERROR(H5E_DATATYPE, H5E_CANTCLOSEOBJ, NULL, "unable to close owned VOL object")
                 new_dt->shared = H5FL_FREE(H5T_shared_t, new_dt->shared);
+            } /* end if */
             new_dt = H5FL_FREE(H5T_t, new_dt);
         } /* end if */
 
@@ -3829,6 +3839,8 @@ done:
     if (ret_value == NULL)
         if (new_dt) {
             HDassert(new_dt->shared);
+            if (new_dt->shared->owned_vol_obj && H5VL_free_object(new_dt->shared->owned_vol_obj) < 0)
+                HDONE_ERROR(H5E_DATATYPE, H5E_CANTCLOSEOBJ, NULL, "unable to close owned VOL object")
             new_dt->shared = H5FL_FREE(H5T_shared_t, new_dt->shared);
             new_dt         = H5FL_FREE(H5T_t, new_dt);
         } /* end if */
@@ -3896,6 +3908,8 @@ H5T_copy_reopen(H5T_t *old_dt)
             /* The object is already open.  Free the H5T_shared_t struct
              * we had been using and use the one that already exists.
              * Not terribly efficient. */
+            if (new_dt->shared->owned_vol_obj && H5VL_free_object(new_dt->shared->owned_vol_obj) < 0)
+                HGOTO_ERROR(H5E_DATATYPE, H5E_CANTCLOSEOBJ, NULL, "unable to close owned VOL object")
             new_dt->shared = H5FL_FREE(H5T_shared_t, new_dt->shared);
             new_dt->shared = reopened_fo;
 
@@ -3932,6 +3946,8 @@ done:
     if (ret_value == NULL)
         if (new_dt) {
             HDassert(new_dt->shared);
+            if (new_dt->shared->owned_vol_obj && H5VL_free_object(new_dt->shared->owned_vol_obj) < 0)
+                HDONE_ERROR(H5E_DATATYPE, H5E_CANTCLOSEOBJ, NULL, "unable to close owned VOL object")
             new_dt->shared = H5FL_FREE(H5T_shared_t, new_dt->shared);
             new_dt         = H5FL_FREE(H5T_t, new_dt);
         } /* end if */
@@ -4026,8 +4042,10 @@ H5T__alloc(void)
 done:
     if (ret_value == NULL)
         if (dt) {
-            if (dt->shared)
+            if (dt->shared) {
+                HDassert(!dt->shared->owned_vol_obj);
                 dt->shared = H5FL_FREE(H5T_shared_t, dt->shared);
+            } /* end if */
             dt = H5FL_FREE(H5T_t, dt);
         } /* end if */
 
@@ -4148,6 +4166,7 @@ H5T_close_real(H5T_t *dt)
         if (H5T__free(dt) < 0)
             HGOTO_ERROR(H5E_DATATYPE, H5E_CANTFREE, FAIL, "unable to free datatype");
 
+        HDassert(!dt->shared->owned_vol_obj);
         dt->shared = H5FL_FREE(H5T_shared_t, dt->shared);
     } /* end if */
     else
@@ -4282,6 +4301,7 @@ H5T__set_size(H5T_t *dt, size_t size)
 
     /* Check args */
     HDassert(dt);
+    HDassert(dt->shared);
     HDassert(size != 0);
     HDassert(H5T_REFERENCE != dt->shared->type);
     HDassert(!(H5T_ENUM == dt->shared->type && 0 == dt->shared->u.enumer.nmembs));
@@ -4469,11 +4489,38 @@ H5T_get_size(const H5T_t *dt)
 
     /* check args */
     HDassert(dt);
+    HDassert(dt->shared);
 
     FUNC_LEAVE_NOAPI(dt->shared->size)
 } /* end H5T_get_size() */
 
 /*-------------------------------------------------------------------------
+ * Function:  H5T_get_force_conv
+ *
+ * Purpose:   Determines if the type has forced conversion. This will be
+ *            true if and only if the type keeps a pointer to a file VOL
+ *            object internally.
+ *
+ * Return:    TRUE/FALSE (never fails)
+ *
+ * Programmer:    Neil Fortner
+ *        Thursday, January  21, 2021
+ *-------------------------------------------------------------------------
+ */
+hbool_t
+H5T_get_force_conv(const H5T_t *dt)
+{
+    /* Use FUNC_ENTER_NOAPI_NOINIT_NOERR here to avoid performance issues */
+    FUNC_ENTER_NOAPI_NOINIT_NOERR
+
+    /* check args */
+    HDassert(dt);
+    HDassert(dt->shared);
+
+    FUNC_LEAVE_NOAPI(dt->shared->force_conv)
+} /* end H5T_get_force_conv() */
+
+/*-------------------------------------------------------------------------
  * Function:  H5T_cmp
  *
  * Purpose:   Compares two data types.
@@ -4509,6 +4556,9 @@ H5T_cmp(const H5T_t *dt1, const H5T_t *dt2, hbool_t superset)
     if (dt1 == dt2)
         HGOTO_DONE(0);
 
+    HDassert(dt1->shared);
+    HDassert(dt2->shared);
+
     /* compare */
     if (dt1->shared->type < dt2->shared->type)
         HGOTO_DONE(-1);
@@ -4914,6 +4964,10 @@ H5T_cmp(const H5T_t *dt1, const H5T_t *dt2, hbool_t superset)
                         HGOTO_DONE(-1);
                     if (dt1->shared->u.atomic.u.r.loc > dt2->shared->u.atomic.u.r.loc)
                         HGOTO_DONE(1);
+                    if (dt1->shared->u.atomic.u.r.file < dt2->shared->u.atomic.u.r.file)
+                        HGOTO_DONE(-1);
+                    if (dt1->shared->u.atomic.u.r.file > dt2->shared->u.atomic.u.r.file)
+                        HGOTO_DONE(1);
                     break;
 
                 case H5T_NO_CLASS:
@@ -6295,6 +6349,7 @@ H5T_own_vol_obj(H5T_t *dt, H5VL_object_t *vol_obj)
 
     /* Take ownership */
     dt->shared->owned_vol_obj = vol_obj;
+    (void)H5VL_object_inc_rc(vol_obj);
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
diff --git a/src/H5Tcommit.c b/src/H5Tcommit.c
index 41191fa..5ce6f3a 100644
--- a/src/H5Tcommit.c
+++ b/src/H5Tcommit.c
@@ -143,11 +143,8 @@ H5T__commit_api_common(hid_t loc_id, const char *name, hid_t type_id, hid_t lcpl
         HGOTO_ERROR(H5E_DATATYPE, H5E_CANTINIT, FAIL, "unable to commit datatype")
 
     /* Set up VOL object */
-    if (NULL == (new_obj = H5FL_CALLOC(H5VL_object_t)))
-        HGOTO_ERROR(H5E_DATATYPE, H5E_CANTALLOC, FAIL, "can't allocate top object structure")
-    new_obj->connector = (*vol_obj_ptr)->connector;
-    new_obj->connector->nrefs++;
-    new_obj->data = data;
+    if (NULL == (new_obj = H5VL_create_object(data, (*vol_obj_ptr)->connector)))
+        HGOTO_ERROR(H5E_DATATYPE, H5E_CANTALLOC, FAIL, "can't create VOL object for committed datatype")
 
     /* Set the committed type object to the VOL connector pointer in the H5T_t struct */
     dt->vol_obj = new_obj;
@@ -370,11 +367,8 @@ H5Tcommit_anon(hid_t loc_id, hid_t type_id, hid_t tcpl_id, hid_t tapl_id)
         HGOTO_ERROR(H5E_DATATYPE, H5E_CANTINIT, FAIL, "unable to commit datatype")
 
     /* Setup VOL object */
-    if (NULL == (new_obj = H5FL_CALLOC(H5VL_object_t)))
-        HGOTO_ERROR(H5E_DATATYPE, H5E_CANTALLOC, FAIL, "can't allocate top object structure")
-    new_obj->connector = vol_obj->connector;
-    new_obj->connector->nrefs++;
-    new_obj->data = dt;
+    if (NULL == (new_obj = H5VL_create_object(dt, vol_obj->connector)))
+        HGOTO_ERROR(H5E_DATATYPE, H5E_CANTALLOC, FAIL, "can't create VOL object for committed datatype")
 
     /* Set the committed type object to the VOL connector pointer in the H5T_t struct */
     type->vol_obj = new_obj;
@@ -1114,8 +1108,11 @@ H5T_open(const H5G_loc_t *loc)
 done:
     if (ret_value == NULL) {
         if (dt) {
-            if (shared_fo == NULL) /* Need to free shared fo */
+            if (shared_fo == NULL) { /* Need to free shared fo */
+                if (dt->shared->owned_vol_obj && H5VL_free_object(dt->shared->owned_vol_obj) < 0)
+                    HDONE_ERROR(H5E_DATATYPE, H5E_CANTCLOSEOBJ, NULL, "unable to close owned VOL object")
                 dt->shared = H5FL_FREE(H5T_shared_t, dt->shared);
+            } /* end if */
 
             H5O_loc_free(&(dt->oloc));
             H5G_name_free(&(dt->path));
diff --git a/src/H5Tconv.c b/src/H5Tconv.c
index d8e4759..92b8ae1 100644
--- a/src/H5Tconv.c
+++ b/src/H5Tconv.c
@@ -2010,7 +2010,7 @@ H5T__conv_struct_init(H5T_t *src, H5T_t *dst, H5T_cdata_t *cdata)
         priv->subset_info.copy_size = 0;
 
         /*
-         * Insure that members are sorted.
+         * Ensure that members are sorted.
          */
         H5T__sort_value(src, NULL);
         H5T__sort_value(dst, NULL);
diff --git a/src/H5Tdeprec.c b/src/H5Tdeprec.c
index a6a6631..fa14151 100644
--- a/src/H5Tdeprec.c
+++ b/src/H5Tdeprec.c
@@ -134,11 +134,8 @@ H5Tcommit1(hid_t loc_id, const char *name, hid_t type_id)
         HGOTO_ERROR(H5E_DATATYPE, H5E_CANTINIT, FAIL, "unable to commit datatype")
 
     /* Set up VOL object */
-    if (NULL == (new_obj = H5FL_CALLOC(H5VL_object_t)))
-        HGOTO_ERROR(H5E_DATATYPE, H5E_NOSPACE, FAIL, "can't allocate top object structure")
-    new_obj->connector = vol_obj->connector;
-    new_obj->connector->nrefs++;
-    new_obj->data = data;
+    if (NULL == (new_obj = H5VL_create_object(data, vol_obj->connector)))
+        HGOTO_ERROR(H5E_DATATYPE, H5E_CANTALLOC, FAIL, "can't create VOL object for committed datatype")
 
     /* Set the committed type object to the VOL connector pointer in the H5T_t struct */
     dt->vol_obj = new_obj;
diff --git a/src/H5Tpkg.h b/src/H5Tpkg.h
index e96921f..e9991d8 100644
--- a/src/H5Tpkg.h
+++ b/src/H5Tpkg.h
@@ -860,7 +860,7 @@ H5_DLL void     H5T__bit_neg(uint8_t *buf, size_t start, size_t size);
 /* VL functions */
 H5_DLL H5T_t *H5T__vlen_create(const H5T_t *base);
 H5_DLL herr_t H5T__vlen_reclaim(void *elem, const H5T_t *dt, H5T_vlen_alloc_info_t *alloc_info);
-H5_DLL htri_t H5T__vlen_set_loc(const H5T_t *dt, H5VL_object_t *file, H5T_loc_t loc);
+H5_DLL htri_t H5T__vlen_set_loc(H5T_t *dt, H5VL_object_t *file, H5T_loc_t loc);
 
 /* Array functions */
 H5_DLL H5T_t *H5T__array_create(H5T_t *base, unsigned ndims, const hsize_t dim[/* ndims */]);
@@ -869,7 +869,7 @@ H5_DLL int    H5T__get_array_dims(const H5T_t *dt, hsize_t dims[]);
 
 /* Reference functions */
 H5_DLL herr_t H5T__ref_reclaim(void *elem, const H5T_t *dt);
-H5_DLL htri_t H5T__ref_set_loc(const H5T_t *dt, H5VL_object_t *file, H5T_loc_t loc);
+H5_DLL htri_t H5T__ref_set_loc(H5T_t *dt, H5VL_object_t *file, H5T_loc_t loc);
 
 /* Compound functions */
 H5_DLL herr_t H5T__insert(H5T_t *parent, const char *name, size_t offset, const H5T_t *member);
diff --git a/src/H5Tprivate.h b/src/H5Tprivate.h
index 52f1c14..862ee1f 100644
--- a/src/H5Tprivate.h
+++ b/src/H5Tprivate.h
@@ -41,11 +41,13 @@ typedef struct H5T_t H5T_t;
 #define H5T_GET_SHARED(T)           ((T)->shared)
 #define H5T_GET_MEMBER_OFFSET(T, I) ((T)->u.compnd.memb[I].offset)
 #define H5T_GET_MEMBER_SIZE(T, I)   ((T)->u.compnd.memb[I].shared->size)
+#define H5T_GET_FORCE_CONV(T)       ((T)>shared->force_conv)
 #else /* H5T_MODULE */
 #define H5T_GET_SIZE(T)             (H5T_get_size(T))
 #define H5T_GET_SHARED(T)           (H5T_get_shared(T))
 #define H5T_GET_MEMBER_OFFSET(T, I) (H5T_get_member_offset((T), (I)))
 #define H5T_GET_MEMBER_SIZE(T, I)   (H5T_get_member_size((T), (I)))
+#define H5T_GET_FORCE_CONV(T)       (H5T_get_force_conv(T))
 #endif /* H5T_MODULE */
 
 /* Forward references of package typedefs (declared in H5Tpkg.h) */
@@ -114,6 +116,7 @@ H5_DLL H5T_t *     H5T_get_super(const H5T_t *dt);
 H5_DLL H5T_class_t H5T_get_class(const H5T_t *dt, htri_t internal);
 H5_DLL htri_t      H5T_detect_class(const H5T_t *dt, H5T_class_t cls, hbool_t from_api);
 H5_DLL size_t      H5T_get_size(const H5T_t *dt);
+H5_DLL hbool_t     H5T_get_force_conv(const H5T_t *dt);
 H5_DLL int         H5T_cmp(const H5T_t *dt1, const H5T_t *dt2, hbool_t superset);
 H5_DLL herr_t      H5T_encode(H5T_t *obj, unsigned char *buf, size_t *nalloc);
 H5_DLL H5T_t *           H5T_decode(size_t buf_size, const unsigned char *buf);
diff --git a/src/H5Tref.c b/src/H5Tref.c
index 8d7dca2..9c6477b 100644
--- a/src/H5Tref.c
+++ b/src/H5Tref.c
@@ -156,7 +156,7 @@ static const H5T_ref_class_t H5T_ref_dsetreg_disk_g = {
  *-------------------------------------------------------------------------
  */
 htri_t
-H5T__ref_set_loc(const H5T_t *dt, H5VL_object_t *file, H5T_loc_t loc)
+H5T__ref_set_loc(H5T_t *dt, H5VL_object_t *file, H5T_loc_t loc)
 {
     htri_t ret_value = FALSE; /* Indicate success, but no location change */
 
@@ -180,6 +180,13 @@ H5T__ref_set_loc(const H5T_t *dt, H5VL_object_t *file, H5T_loc_t loc)
             /* Mark this type as being stored in memory */
             dt->shared->u.atomic.u.r.loc = H5T_LOC_MEMORY;
 
+            /* Release owned file */
+            if (dt->shared->owned_vol_obj) {
+                if(H5VL_free_object(dt->shared->owned_vol_obj) < 0)
+                    HGOTO_ERROR(H5E_REFERENCE, H5E_CANTCLOSEOBJ, FAIL, "unable to close owned VOL object")
+                dt->shared->owned_vol_obj = NULL;
+            } /* end if */
+
             /* Reset file ID (since this reference is in memory) */
             dt->shared->u.atomic.u.r.file = file; /* file is NULL */
 
@@ -220,6 +227,10 @@ H5T__ref_set_loc(const H5T_t *dt, H5VL_object_t *file, H5T_loc_t loc)
             /* Set file pointer (since this reference is on disk) */
             dt->shared->u.atomic.u.r.file = file;
 
+            /* dt now owns a reference to file */
+            if (H5T_own_vol_obj(dt, file) < 0)
+                HGOTO_ERROR(H5E_REFERENCE, H5E_CANTINIT, FAIL, "can't give ownership of VOL object")
+
             if (dt->shared->u.atomic.u.r.rtype == H5R_OBJECT1) {
                 H5F_t *f;
 
diff --git a/src/H5Tvlen.c b/src/H5Tvlen.c
index e2d8d2a..20dab84 100644
--- a/src/H5Tvlen.c
+++ b/src/H5Tvlen.c
@@ -245,7 +245,7 @@ done:
  *-------------------------------------------------------------------------
  */
 htri_t
-H5T__vlen_set_loc(const H5T_t *dt, H5VL_object_t *file, H5T_loc_t loc)
+H5T__vlen_set_loc(H5T_t *dt, H5VL_object_t *file, H5T_loc_t loc)
 {
     H5VL_file_cont_info_t cont_info = {H5VL_CONTAINER_INFO_VERSION, 0, 0, 0};
     htri_t                ret_value = FALSE; /* Indicate success, but no location change */
@@ -282,6 +282,13 @@ H5T__vlen_set_loc(const H5T_t *dt, H5VL_object_t *file, H5T_loc_t loc)
                 else
                     HDassert(0 && "Invalid VL type");
 
+                /* Release owned file */
+                if (dt->shared->owned_vol_obj) {
+                    if(H5VL_free_object(dt->shared->owned_vol_obj) < 0)
+                        HGOTO_ERROR(H5E_DATATYPE, H5E_CANTCLOSEOBJ, FAIL, "unable to close owned VOL object")
+                    dt->shared->owned_vol_obj = NULL;
+                } /* end if */
+
                 /* Reset file pointer (since this VL is in memory) */
                 dt->shared->u.vlen.file = NULL;
                 break;
@@ -307,6 +314,10 @@ H5T__vlen_set_loc(const H5T_t *dt, H5VL_object_t *file, H5T_loc_t loc)
 
                 /* Set file ID (since this VL is on disk) */
                 dt->shared->u.vlen.file = file;
+
+                /* dt now owns a reference to file */
+                if (H5T_own_vol_obj(dt, file) < 0)
+                    HGOTO_ERROR(H5E_DATATYPE, H5E_CANTINIT, FAIL, "can't give ownership of VOL object")
                 break;
 
             case H5T_LOC_BADLOC:
diff --git a/src/H5VL.c b/src/H5VL.c
index c1f8adb..628d6bb 100644
--- a/src/H5VL.c
+++ b/src/H5VL.c
@@ -683,8 +683,9 @@ H5VLget_file_type(void *file_obj, hid_t connector_id, hid_t dtype_id)
     if (NULL == (dtype = (H5T_t *)H5I_object_verify(dtype_id, H5I_DATATYPE)))
         HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a data type")
 
-    /* Create VOL object for file */
-    if (NULL == (file_vol_obj = H5VL_create_object_using_vol_id(H5I_FILE, file_obj, connector_id)))
+    /* Create VOL object for file if necessary (force_conv will be TRUE if and
+     * only if file needs to be passed to H5T_set_loc) */
+    if (H5T_GET_FORCE_CONV(dtype) && (NULL == (file_vol_obj = H5VL_create_object_using_vol_id(H5I_FILE, file_obj, connector_id))))
         HGOTO_ERROR(H5E_VOL, H5E_CANTCREATE, FAIL, "can't create VOL object")
 
     /* Copy the datatype */
@@ -701,10 +702,12 @@ H5VLget_file_type(void *file_obj, hid_t connector_id, hid_t dtype_id)
     if (H5T_set_loc(file_type, file_vol_obj, H5T_LOC_DISK) < 0)
         HGOTO_ERROR(H5E_VOL, H5E_CANTINIT, FAIL, "can't set datatype location")
 
-    /* file_type now owns file_vol_obj */
-    if (H5T_own_vol_obj(file_type, file_vol_obj) < 0)
-        HGOTO_ERROR(H5E_VOL, H5E_CANTINIT, FAIL, "can't give ownership of VOL object")
-    file_vol_obj = NULL;
+    /* Release our reference to file_type */
+    if (file_vol_obj) {
+        if (H5VL_free_object(file_vol_obj) < 0)
+            HGOTO_ERROR(H5E_VOL, H5E_CANTDEC, FAIL, "unable to free VOL object")
+        file_vol_obj = NULL;
+    } /* end if */
 
     /* Set return value */
     ret_value = file_type_id;
diff --git a/src/H5VLint.c b/src/H5VLint.c
index b7823fb..033327d 100644
--- a/src/H5VLint.c
+++ b/src/H5VLint.c
@@ -568,6 +568,7 @@ H5VL__new_vol_obj(H5I_type_t type, void *object, H5VL_t *vol_connector, hbool_t
     } /* end if */
     else
         new_vol_obj->data = object;
+    new_vol_obj->rc = 1;
 
     /* Bump the reference count on the VOL connector */
     H5VL_conn_inc_rc(vol_connector);
@@ -844,6 +845,7 @@ H5VL_create_object(void *object, H5VL_t *vol_connector)
         HGOTO_ERROR(H5E_VOL, H5E_CANTALLOC, NULL, "can't allocate memory for VOL object")
     ret_value->connector = vol_connector;
     ret_value->data      = object;
+    ret_value->rc        = 1;
 
     /* Bump the reference count on the VOL connector */
     H5VL_conn_inc_rc(vol_connector);
@@ -981,6 +983,27 @@ done:
 } /* end H5VL_conn_dec_rc() */
 
 /*-------------------------------------------------------------------------
+ * Function:    H5VL_object_inc_rc
+ *
+ * Purpose:     Wrapper to increment the ref count on a VOL object.
+ *
+ * Return:      SUCCEED/FAIL
+ *
+ *-------------------------------------------------------------------------
+ */
+hsize_t
+H5VL_object_inc_rc(H5VL_object_t *vol_obj)
+{
+    FUNC_ENTER_NOAPI_NOERR_NOFS
+
+    /* Check arguments */
+    HDassert(vol_obj);
+
+    /* Increment refcount for object and return */
+    FUNC_LEAVE_NOAPI(++vol_obj->rc)
+} /* end H5VL_object_inc_rc() */
+
+/*-------------------------------------------------------------------------
  * Function:    H5VL_free_object
  *
  * Purpose:     Wrapper to unregister an object ID with a VOL aux struct
@@ -1000,11 +1023,13 @@ H5VL_free_object(H5VL_object_t *vol_obj)
     /* Check arguments */
     HDassert(vol_obj);
 
-    /* Decrement refcount on connector */
-    if (H5VL_conn_dec_rc(vol_obj->connector) < 0)
-        HGOTO_ERROR(H5E_VOL, H5E_CANTDEC, FAIL, "unable to decrement ref count on VOL connector")
+    if(--vol_obj->rc == 0) {
+        /* Decrement refcount on connector */
+        if (H5VL_conn_dec_rc(vol_obj->connector) < 0)
+            HGOTO_ERROR(H5E_VOL, H5E_CANTDEC, FAIL, "unable to decrement ref count on VOL connector")
 
-    vol_obj = H5FL_FREE(H5VL_object_t, vol_obj);
+        vol_obj = H5FL_FREE(H5VL_object_t, vol_obj);
+    } /* end if */
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
diff --git a/src/H5VLprivate.h b/src/H5VLprivate.h
index a224a14..880efd3 100644
--- a/src/H5VLprivate.h
+++ b/src/H5VLprivate.h
@@ -37,6 +37,7 @@ typedef struct H5VL_t {
 typedef struct H5VL_object_t {
     void *  data;      /* Pointer to connector-managed data for this object    */
     H5VL_t *connector; /* Pointer to VOL connector struct                      */
+    size_t rc;         /* Reference count                                      */
 } H5VL_object_t;
 
 /* Internal structure to hold the connector ID & info for FAPLs */
@@ -90,6 +91,7 @@ H5_DLL void *H5VL_object_verify(hid_t id, H5I_type_t obj_type);
 H5_DLL H5VL_object_t *H5VL_vol_object(hid_t id);
 H5_DLL H5VL_object_t *H5VL_create_object(void *object, H5VL_t *vol_connector);
 H5_DLL H5VL_object_t *H5VL_create_object_using_vol_id(H5I_type_t type, void *obj, hid_t connector_id);
+H5_DLL hsize_t        H5VL_object_inc_rc(H5VL_object_t *obj);
 H5_DLL herr_t         H5VL_free_object(H5VL_object_t *obj);
 H5_DLL herr_t         H5VL_object_is_native(const H5VL_object_t *obj, hbool_t *is_native);
 H5_DLL herr_t         H5VL_file_is_same(const H5VL_object_t *vol_obj1, const H5VL_object_t *vol_obj2,