diff --git a/src/core/ddsc/src/dds__types.h b/src/core/ddsc/src/dds__types.h
index ba2319a..ea54811 100644
--- a/src/core/ddsc/src/dds__types.h
+++ b/src/core/ddsc/src/dds__types.h
@@ -103,41 +103,45 @@ dds_domain;
 
 struct dds_entity;
 typedef struct dds_entity_deriver {
-    /* Close can be used to terminate (blocking) actions on a entity before actually deleting it. */
-    dds_return_t (*close)(struct dds_entity *e) ddsrt_nonnull_all;
-    /* Delete is used to actually free the entity. */
-    dds_return_t (*delete)(struct dds_entity *e) ddsrt_nonnull_all;
-    dds_return_t (*set_qos)(struct dds_entity *e, const dds_qos_t *qos, bool enabled) ddsrt_nonnull_all;
-    dds_return_t (*validate_status)(uint32_t mask);
-    dds_return_t (*get_instance_hdl)(struct dds_entity *e, dds_instance_handle_t *i) ddsrt_nonnull_all;
-}
-dds_entity_deriver;
+  /* Close can be used to terminate (blocking) actions on a entity before actually deleting it. */
+  dds_return_t (*close)(struct dds_entity *e) ddsrt_nonnull_all;
+  /* Delete is used to actually free the entity. */
+  dds_return_t (*delete)(struct dds_entity *e) ddsrt_nonnull_all;
+  dds_return_t (*set_qos)(struct dds_entity *e, const dds_qos_t *qos, bool enabled) ddsrt_nonnull_all;
+  dds_return_t (*validate_status)(uint32_t mask);
+} dds_entity_deriver;
 
 typedef void (*dds_entity_callback)(dds_entity_t observer, dds_entity_t observed, uint32_t status);
 
-typedef struct dds_entity_observer
-{
-    dds_entity_callback m_cb;
-    dds_entity_t m_observer;
-    struct dds_entity_observer *m_next;
-}
-dds_entity_observer;
+typedef struct dds_entity_observer {
+  dds_entity_callback m_cb;
+  dds_entity_t m_observer;
+  struct dds_entity_observer *m_next;
+} dds_entity_observer;
 
-typedef struct dds_entity
-{
-  struct dds_handle_link m_hdllink;
-  dds_entity_kind_t m_kind;
-  dds_entity_deriver m_deriver;
-  uint32_t m_refc;
-  struct dds_entity * m_next;
-  struct dds_entity * m_parent;
-  struct dds_entity * m_children;
-  struct dds_entity * m_participant;
-  struct dds_domain * m_domain;
-  dds_qos_t * m_qos;
-  dds_domainid_t m_domainid;
-  nn_guid_t m_guid;
-  uint32_t m_flags;
+typedef struct dds_entity {
+  struct dds_handle_link m_hdllink; /* handle is constant, cnt_flags private to dds_handle.c */
+  dds_entity_kind_t m_kind;         /* constant */
+  dds_entity_deriver m_deriver;     /* constant; FIXME: no point in having function pointers embedded */
+  uint32_t m_refc;                  /* [m_mutex] */
+  struct dds_entity *m_next;        /* [m_mutex] */
+  struct dds_entity *m_parent;      /* constant */
+  struct dds_entity *m_children;    /* [m_mutex] */
+  struct dds_entity *m_participant; /* constant */
+  struct dds_domain *m_domain;      /* constant */
+  dds_qos_t *m_qos;                 /* [m_mutex] */
+  dds_domainid_t m_domainid;        /* constant; FIXME: why? hardly ever used, m_domain should give that info, too */
+  nn_guid_t m_guid;                 /* ~ constant: FIXME: set during creation, but possibly after becoming visible */
+  dds_instance_handle_t m_iid;      /* ~ constant: FIXME: like GUID */
+  uint32_t m_flags;                 /* [m_mutex] */
+
+  /* Allowed:
+     - locking parent->...->m_mutex while holding m_mutex
+     - locking topic::m_mutex while holding {publisher,subscriber}::m_mutex
+       (no hierarchical relationship there)
+     - locking topic::m_mutex while holding {reader,writer}::m_mutex
+     - locking observers_lock while holding m_mutex
+   */
   ddsrt_mutex_t m_mutex;
   ddsrt_cond_t m_cond;
 
diff --git a/src/core/ddsc/src/dds_entity.c b/src/core/ddsc/src/dds_entity.c
index 4b51023..2fc5f25 100644
--- a/src/core/ddsc/src/dds_entity.c
+++ b/src/core/ddsc/src/dds_entity.c
@@ -889,14 +889,10 @@ dds_return_t dds_get_instance_handle (dds_entity_t entity, dds_instance_handle_t
   if (ihdl == NULL)
     return DDS_RETCODE_BAD_PARAMETER;
 
-  if ((ret = dds_entity_lock (entity, DDS_KIND_DONTCARE, &e)) != DDS_RETCODE_OK)
+  if ((ret = dds_entity_claim (entity, &e)) != DDS_RETCODE_OK)
     return ret;
-
-  if (e->m_deriver.get_instance_hdl)
-    ret = e->m_deriver.get_instance_hdl (e, ihdl);
-  else
-    ret = DDS_RETCODE_ILLEGAL_OPERATION;
-  dds_entity_unlock(e);
+  *ihdl = e->m_iid;
+  dds_entity_release(e);
   return ret;
 }
 
diff --git a/src/core/ddsc/src/dds_guardcond.c b/src/core/ddsc/src/dds_guardcond.c
index 8dcb956..5e7e83b 100644
--- a/src/core/ddsc/src/dds_guardcond.c
+++ b/src/core/ddsc/src/dds_guardcond.c
@@ -14,6 +14,7 @@
 #include "dds__reader.h"
 #include "dds__guardcond.h"
 #include "dds__participant.h"
+#include "dds/ddsi/ddsi_iid.h"
 #include "dds/ddsi/q_ephash.h"
 #include "dds/ddsi/q_entity.h"
 #include "dds/ddsi/q_thread.h"
@@ -29,8 +30,9 @@ dds_entity_t dds_create_guardcondition (dds_entity_t participant)
     return rc;
   else
   {
-    dds_guardcond * gcond = dds_alloc (sizeof (*gcond));
+    dds_guardcond *gcond = dds_alloc (sizeof (*gcond));
     dds_entity_t hdl = dds_entity_init (&gcond->m_entity, &pp->m_entity, DDS_KIND_COND_GUARD, NULL, NULL, 0);
+    gcond->m_entity.m_iid = ddsi_iid_gen ();
     dds_participant_unlock (pp);
     return hdl;
   }
diff --git a/src/core/ddsc/src/dds_participant.c b/src/core/ddsc/src/dds_participant.c
index fea399b..57aca98 100644
--- a/src/core/ddsc/src/dds_participant.c
+++ b/src/core/ddsc/src/dds_participant.c
@@ -64,14 +64,6 @@ static dds_return_t dds_participant_delete (dds_entity *e)
   return DDS_RETCODE_OK;
 }
 
-static dds_return_t dds_participant_instance_hdl (dds_entity *e, dds_instance_handle_t *i) ddsrt_nonnull_all;
-
-static dds_return_t dds_participant_instance_hdl (dds_entity *e, dds_instance_handle_t *i)
-{
-  *i = participant_instance_id (&e->m_guid);
-  return DDS_RETCODE_OK;
-}
-
 static dds_return_t dds_participant_qos_set (dds_entity *e, const dds_qos_t *qos, bool enabled)
 {
   /* note: e->m_qos is still the old one to allow for failure here */
@@ -134,11 +126,11 @@ dds_entity_t dds_create_participant (const dds_domainid_t domain, const dds_qos_
     goto err_entity_init;
 
   pp->m_entity.m_guid = guid;
+  pp->m_entity.m_iid = get_entity_instance_id (&guid);
   pp->m_entity.m_domain = dds_domain_create (dds_domain_default ());
   pp->m_entity.m_domainid = dds_domain_default ();
   pp->m_entity.m_deriver.delete = dds_participant_delete;
   pp->m_entity.m_deriver.set_qos = dds_participant_qos_set;
-  pp->m_entity.m_deriver.get_instance_hdl = dds_participant_instance_hdl;
   pp->m_entity.m_deriver.validate_status = dds_participant_status_validate;
   pp->m_builtin_subscriber = 0;
 
diff --git a/src/core/ddsc/src/dds_publisher.c b/src/core/ddsc/src/dds_publisher.c
index 307a40b..850623d 100644
--- a/src/core/ddsc/src/dds_publisher.c
+++ b/src/core/ddsc/src/dds_publisher.c
@@ -24,15 +24,6 @@ DECL_ENTITY_LOCK_UNLOCK (extern inline, dds_publisher)
 
 #define DDS_PUBLISHER_STATUS_MASK   (0u)
 
-static dds_return_t dds_publisher_instance_hdl (dds_entity *e, dds_instance_handle_t *i) ddsrt_nonnull_all;
-
-static dds_return_t dds_publisher_instance_hdl (dds_entity *e, dds_instance_handle_t *i)
-{
-  /* FIXME: Get/generate proper handle. */
-  (void) e; (void) i;
-  return DDS_RETCODE_UNSUPPORTED;
-}
-
 static dds_return_t dds_publisher_qos_set (dds_entity *e, const dds_qos_t *qos, bool enabled)
 {
   /* note: e->m_qos is still the old one to allow for failure here */
@@ -70,8 +61,8 @@ dds_entity_t dds_create_publisher (dds_entity_t participant, const dds_qos_t *qo
   }
   pub = dds_alloc (sizeof (*pub));
   hdl = dds_entity_init (&pub->m_entity, &par->m_entity, DDS_KIND_PUBLISHER, new_qos, listener, DDS_PUBLISHER_STATUS_MASK);
+  pub->m_entity.m_iid = ddsi_iid_gen ();
   pub->m_entity.m_deriver.set_qos = dds_publisher_qos_set;
-  pub->m_entity.m_deriver.get_instance_hdl = dds_publisher_instance_hdl;
   pub->m_entity.m_deriver.validate_status = dds_publisher_status_validate;
   dds_participant_unlock (par);
   return hdl;
diff --git a/src/core/ddsc/src/dds_readcond.c b/src/core/ddsc/src/dds_readcond.c
index c5b0ace..0de3879 100644
--- a/src/core/ddsc/src/dds_readcond.c
+++ b/src/core/ddsc/src/dds_readcond.c
@@ -14,6 +14,7 @@
 #include "dds__readcond.h"
 #include "dds__rhc.h"
 #include "dds__entity.h"
+#include "dds/ddsi/ddsi_iid.h"
 #include "dds/ddsi/q_ephash.h"
 #include "dds/ddsi/q_entity.h"
 #include "dds/ddsi/q_thread.h"
@@ -31,6 +32,7 @@ dds_readcond *dds_create_readcond (dds_reader *rd, dds_entity_kind_t kind, uint3
   dds_readcond *cond = dds_alloc (sizeof (*cond));
   assert ((kind == DDS_KIND_COND_READ && filter == 0) || (kind == DDS_KIND_COND_QUERY && filter != 0));
   (void) dds_entity_init (&cond->m_entity, &rd->m_entity, kind, NULL, NULL, 0);
+  cond->m_entity.m_iid = ddsi_iid_gen ();
   cond->m_entity.m_deriver.delete = dds_readcond_delete;
   cond->m_rhc = rd->m_rd->rhc;
   cond->m_sample_states = mask & DDS_ANY_SAMPLE_STATE;
diff --git a/src/core/ddsc/src/dds_reader.c b/src/core/ddsc/src/dds_reader.c
index 9fcecd6..dd40d40 100644
--- a/src/core/ddsc/src/dds_reader.c
+++ b/src/core/ddsc/src/dds_reader.c
@@ -39,14 +39,6 @@ DECL_ENTITY_LOCK_UNLOCK (extern inline, dds_reader)
                          DDS_SAMPLE_LOST_STATUS                  |\
                          DDS_SUBSCRIPTION_MATCHED_STATUS)
 
-static dds_return_t dds_reader_instance_hdl (dds_entity *e, dds_instance_handle_t *i) ddsrt_nonnull_all;
-
-static dds_return_t dds_reader_instance_hdl (dds_entity *e, dds_instance_handle_t *i)
-{
-  *i = reader_instance_id (&e->m_guid);
-  return DDS_RETCODE_OK;
-}
-
 static dds_return_t dds_reader_close (dds_entity *e) ddsrt_nonnull_all;
 
 static dds_return_t dds_reader_close (dds_entity *e)
@@ -392,7 +384,6 @@ dds_entity_t dds_create_reader (dds_entity_t participant_or_subscriber, dds_enti
   rd->m_entity.m_deriver.delete = dds_reader_delete;
   rd->m_entity.m_deriver.set_qos = dds_reader_qos_set;
   rd->m_entity.m_deriver.validate_status = dds_reader_status_validate;
-  rd->m_entity.m_deriver.get_instance_hdl = dds_reader_instance_hdl;
 
   /* Extra claim of this reader to make sure that the delete waits until DDSI
      has deleted its reader as well. This can be known through the callback. */
@@ -407,6 +398,7 @@ dds_entity_t dds_create_reader (dds_entity_t participant_or_subscriber, dds_enti
   ddsrt_mutex_lock (&tp->m_entity.m_mutex);
   assert (ret == DDS_RETCODE_OK); /* FIXME: can be out-of-resources at the very least */
   thread_state_asleep (lookup_thread_state ());
+  rd->m_entity.m_iid = get_entity_instance_id (&rd->m_entity.m_guid);
 
   /* For persistent data register reader with durability */
   if (dds_global.m_dur_reader && (rd->m_entity.m_qos->durability.kind > DDS_DURABILITY_TRANSIENT_LOCAL)) {
diff --git a/src/core/ddsc/src/dds_subscriber.c b/src/core/ddsc/src/dds_subscriber.c
index 181a6af..084558d 100644
--- a/src/core/ddsc/src/dds_subscriber.c
+++ b/src/core/ddsc/src/dds_subscriber.c
@@ -23,15 +23,6 @@ DECL_ENTITY_LOCK_UNLOCK (extern inline, dds_subscriber)
 #define DDS_SUBSCRIBER_STATUS_MASK                               \
                         (DDS_DATA_ON_READERS_STATUS)
 
-static dds_return_t dds_subscriber_instance_hdl (dds_entity *e, dds_instance_handle_t *i) ddsrt_nonnull_all;
-
-static dds_return_t dds_subscriber_instance_hdl (dds_entity *e, dds_instance_handle_t *i)
-{
-  (void) e; (void) i;
-  /* FIXME: Get/generate proper handle. */
-  return DDS_RETCODE_UNSUPPORTED;
-}
-
 static dds_return_t dds_subscriber_qos_set (dds_entity *e, const dds_qos_t *qos, bool enabled)
 {
   /* note: e->m_qos is still the old one to allow for failure here */
@@ -64,9 +55,9 @@ dds_entity_t dds__create_subscriber_l (dds_participant *participant, const dds_q
 
   sub = dds_alloc (sizeof (*sub));
   subscriber = dds_entity_init (&sub->m_entity, &participant->m_entity, DDS_KIND_SUBSCRIBER, new_qos, listener, DDS_SUBSCRIBER_STATUS_MASK);
+  sub->m_entity.m_iid = ddsi_iid_gen ();
   sub->m_entity.m_deriver.set_qos = dds_subscriber_qos_set;
   sub->m_entity.m_deriver.validate_status = dds_subscriber_status_validate;
-  sub->m_entity.m_deriver.get_instance_hdl = dds_subscriber_instance_hdl;
   return subscriber;
 }
 
diff --git a/src/core/ddsc/src/dds_topic.c b/src/core/ddsc/src/dds_topic.c
index 90bf553..d7f04c7 100644
--- a/src/core/ddsc/src/dds_topic.c
+++ b/src/core/ddsc/src/dds_topic.c
@@ -271,6 +271,7 @@ dds_entity_t dds_create_topic_arbitrary (dds_entity_t participant, struct ddsi_s
     /* Create topic */
     top = dds_alloc (sizeof (*top));
     hdl = dds_entity_init (&top->m_entity, &par->m_entity, DDS_KIND_TOPIC, new_qos, listener, DDS_TOPIC_STATUS_MASK);
+    top->m_entity.m_iid = ddsi_iid_gen ();
     top->m_entity.m_deriver.delete = dds_topic_delete;
     top->m_entity.m_deriver.set_qos = dds_topic_qos_set;
     top->m_entity.m_deriver.validate_status = dds_topic_status_validate;
diff --git a/src/core/ddsc/src/dds_waitset.c b/src/core/ddsc/src/dds_waitset.c
index 7bbeefe..004f1e6 100644
--- a/src/core/ddsc/src/dds_waitset.c
+++ b/src/core/ddsc/src/dds_waitset.c
@@ -18,6 +18,7 @@
 #include "dds__querycond.h"
 #include "dds__readcond.h"
 #include "dds__rhc.h"
+#include "dds/ddsi/ddsi_iid.h"
 
 DEFINE_ENTITY_LOCK_UNLOCK (static, dds_waitset, DDS_KIND_WAITSET)
 
@@ -153,6 +154,7 @@ dds_entity_t dds_create_waitset (dds_entity_t participant)
 
   dds_waitset *waitset = dds_alloc (sizeof (*waitset));
   hdl = dds_entity_init (&waitset->m_entity, &par->m_entity, DDS_KIND_WAITSET, NULL, NULL, 0);
+  waitset->m_entity.m_iid = ddsi_iid_gen ();
   waitset->m_entity.m_deriver.close = dds_waitset_close;
   waitset->observed = NULL;
   waitset->triggered = NULL;
diff --git a/src/core/ddsc/src/dds_writer.c b/src/core/ddsc/src/dds_writer.c
index bf55b18..1a404e9 100644
--- a/src/core/ddsc/src/dds_writer.c
+++ b/src/core/ddsc/src/dds_writer.c
@@ -36,14 +36,6 @@ DECL_ENTITY_LOCK_UNLOCK (extern inline, dds_writer)
                          DDS_OFFERED_INCOMPATIBLE_QOS_STATUS     |\
                          DDS_PUBLICATION_MATCHED_STATUS)
 
-static dds_return_t dds_writer_instance_hdl (dds_entity *e, dds_instance_handle_t *i) ddsrt_nonnull_all;
-
-static dds_return_t dds_writer_instance_hdl (dds_entity *e, dds_instance_handle_t *i)
-{
-  *i = writer_instance_id(&e->m_guid);
-  return DDS_RETCODE_OK;
-}
-
 static dds_return_t dds_writer_status_validate (uint32_t mask)
 {
   return (mask & ~DDS_WRITER_STATUS_MASK) ? DDS_RETCODE_BAD_PARAMETER : DDS_RETCODE_OK;
@@ -305,7 +297,6 @@ dds_entity_t dds_create_writer (dds_entity_t participant_or_publisher, dds_entit
   wr->m_entity.m_deriver.delete = dds_writer_delete;
   wr->m_entity.m_deriver.set_qos = dds_writer_qos_set;
   wr->m_entity.m_deriver.validate_status = dds_writer_status_validate;
-  wr->m_entity.m_deriver.get_instance_hdl = dds_writer_instance_hdl;
   wr->m_whc = make_whc (wqos);
 
   /* Extra claim of this writer to make sure that the delete waits until DDSI
@@ -321,6 +312,7 @@ dds_entity_t dds_create_writer (dds_entity_t participant_or_publisher, dds_entit
   ddsrt_mutex_lock (&tp->m_entity.m_mutex);
   assert(rc == DDS_RETCODE_OK);
   thread_state_asleep (lookup_thread_state ());
+  wr->m_entity.m_iid = get_entity_instance_id (&wr->m_entity.m_guid);
   dds_topic_unlock (tp);
   dds_publisher_unlock (pub);
   return writer;
diff --git a/src/core/ddsc/tests/unsupported.c b/src/core/ddsc/tests/unsupported.c
index 417302a..b7e63cb 100644
--- a/src/core/ddsc/tests/unsupported.c
+++ b/src/core/ddsc/tests/unsupported.c
@@ -121,16 +121,19 @@ CU_Test(ddsc_unsupported, dds_get_instance_handle, .init = setup, .fini = teardo
     dds_return_t result;
     dds_instance_handle_t ih;
     static struct index_result pars[] = {
-        {TOP, DDS_RETCODE_ILLEGAL_OPERATION}, /* TODO: Shouldn't this be either supported or unsupported? */
-        {PUB, DDS_RETCODE_UNSUPPORTED},
-        {SUB, DDS_RETCODE_UNSUPPORTED},
-        {RCD, DDS_RETCODE_ILLEGAL_OPERATION},
+        {TOP, DDS_RETCODE_OK},
+        {PUB, DDS_RETCODE_OK},
+        {SUB, DDS_RETCODE_OK},
+        {RCD, DDS_RETCODE_OK},
         {BAD, DDS_RETCODE_BAD_PARAMETER}
     };
 
     for (size_t i=0; i < sizeof (pars) / sizeof (pars[0]);i++) {
         result = dds_get_instance_handle(e[pars[i].index], &ih);
         CU_ASSERT_EQUAL(result, pars[i].exp_res);
+        if (pars[i].exp_res == DDS_RETCODE_OK) {
+          CU_ASSERT(ih > 0);
+        }
     }
 }
 
diff --git a/src/core/ddsi/include/dds/ddsi/q_entity.h b/src/core/ddsi/include/dds/ddsi/q_entity.h
index bb55315..5d6dccb 100644
--- a/src/core/ddsi/include/dds/ddsi/q_entity.h
+++ b/src/core/ddsi/include/dds/ddsi/q_entity.h
@@ -529,6 +529,7 @@ dds_return_t new_participant (struct nn_guid *ppguid, unsigned flags, const stru
 */
 dds_return_t delete_participant (const struct nn_guid *ppguid);
 void update_participant_plist (struct participant *pp, const struct nn_plist *plist);
+uint64_t get_entity_instance_id (const struct nn_guid *guid);
 
 /* To obtain the builtin writer to be used for publishing SPDP, SEDP,
    PMD stuff for PP and its endpoints, given the entityid.  If PP has
@@ -559,7 +560,6 @@ dds_return_t delete_writer_nolinger (const struct nn_guid *guid);
 dds_return_t delete_writer_nolinger_locked (struct writer *wr);
 
 dds_return_t delete_reader (const struct nn_guid *guid);
-uint64_t reader_instance_id (const struct nn_guid *guid);
 
 struct local_orphan_writer {
   struct writer wr;
@@ -593,7 +593,6 @@ void delete_local_orphan_writer (struct local_orphan_writer *wr);
 
 void new_proxy_participant (const struct nn_guid *guid, unsigned bes, unsigned prismtech_bes, const struct nn_guid *privileged_pp_guid, struct addrset *as_default, struct addrset *as_meta, const struct nn_plist *plist, dds_duration_t tlease_dur, nn_vendorid_t vendor, unsigned custom_flags, nn_wctime_t timestamp, seqno_t seq);
 int delete_proxy_participant_by_guid (const struct nn_guid * guid, nn_wctime_t timestamp, int isimplicit);
-uint64_t participant_instance_id (const struct nn_guid *guid);
 
 enum update_proxy_participant_source {
   UPD_PROXYPP_SPDP,
@@ -629,8 +628,6 @@ void update_proxy_writer (struct proxy_writer *pwr, struct addrset *as, const st
 int new_proxy_group (const struct nn_guid *guid, const char *name, const struct dds_qos *xqos, nn_wctime_t timestamp);
 void delete_proxy_group (const struct nn_guid *guid, nn_wctime_t timestamp, int isimplicit);
 
-uint64_t writer_instance_id (const struct nn_guid *guid);
-
 /* Call this to empty all address sets of all writers to stop all outgoing traffic, or to
    rebuild them all (which only makes sense after previously having emptied them all). */
 void rebuild_or_clear_writer_addrsets(int rebuild);
diff --git a/src/core/ddsi/src/q_entity.c b/src/core/ddsi/src/q_entity.c
index 21eea71..1aa7ca0 100644
--- a/src/core/ddsi/src/q_entity.c
+++ b/src/core/ddsi/src/q_entity.c
@@ -3124,20 +3124,6 @@ dds_return_t delete_writer (const struct nn_guid *guid)
   return 0;
 }
 
-uint64_t writer_instance_id (const struct nn_guid *guid)
-{
-    struct entity_common *e;
-    e = (struct entity_common*)ephash_lookup_writer_guid(guid);
-    if (e) {
-        return e->iid;
-    }
-    e = (struct entity_common*)ephash_lookup_proxy_writer_guid(guid);
-    if (e) {
-        return e->iid;
-    }
-    return 0;
-}
-
 /* READER ----------------------------------------------------------- */
 
 #ifdef DDSI_INCLUDE_NETWORK_PARTITIONS
@@ -3464,20 +3450,6 @@ dds_return_t delete_reader (const struct nn_guid *guid)
   return 0;
 }
 
-uint64_t reader_instance_id (const struct nn_guid *guid)
-{
-    struct entity_common *e;
-    e = (struct entity_common*)ephash_lookup_reader_guid(guid);
-    if (e) {
-        return e->iid;
-    }
-    e = (struct entity_common*)ephash_lookup_proxy_reader_guid(guid);
-    if (e) {
-        return e->iid;
-    }
-    return 0;
-}
-
 void update_reader_qos (struct reader *rd, const dds_qos_t *xqos)
 {
   ddsrt_mutex_lock (&rd->e.lock);
@@ -3967,18 +3939,16 @@ int delete_proxy_participant_by_guid (const struct nn_guid * guid, nn_wctime_t t
   return 0;
 }
 
-uint64_t participant_instance_id (const struct nn_guid *guid)
+uint64_t get_entity_instance_id (const struct nn_guid *guid)
 {
-    struct entity_common *e;
-    e = (struct entity_common*)ephash_lookup_participant_guid(guid);
-    if (e) {
-        return e->iid;
-    }
-    e = (struct entity_common*)ephash_lookup_proxy_participant_guid(guid);
-    if (e) {
-        return e->iid;
-    }
-    return 0;
+  struct thread_state1 *ts1 = lookup_thread_state ();
+  struct entity_common *e;
+  uint64_t iid = 0;
+  thread_state_awake (ts1);
+  if ((e = ephash_lookup_guid_untyped (guid)) != NULL)
+    iid = e->iid;
+  thread_state_asleep (ts1);
+  return iid;
 }
 
 /* PROXY-GROUP --------------------------------------------------- */
diff --git a/src/core/ddsi/src/q_ephash.c b/src/core/ddsi/src/q_ephash.c
index d02fcba..4401010 100644
--- a/src/core/ddsi/src/q_ephash.c
+++ b/src/core/ddsi/src/q_ephash.c
@@ -121,6 +121,7 @@ void *ephash_lookup_guid_untyped (const struct nn_guid *guid)
   /* FIXME: could (now) require guid to be first in entity_common; entity_common already is first in entity */
   struct entity_common e;
   e.guid = *guid;
+  assert (thread_is_awake ());
   return ddsrt_chh_lookup (gv.guid_hash->hash, &e);
 }
 
diff --git a/src/core/ddsi/src/q_xevent.c b/src/core/ddsi/src/q_xevent.c
index a7cb357..c1bd837 100644
--- a/src/core/ddsi/src/q_xevent.c
+++ b/src/core/ddsi/src/q_xevent.c
@@ -542,9 +542,9 @@ void xeventq_free (struct xeventq *evq)
       handle_nontimed_xevent (getnext_from_non_timed_xmit_list (evq), xp);
     }
     ddsrt_mutex_unlock (&evq->lock);
-    thread_state_asleep (lookup_thread_state ());
     nn_xpack_send (xp, false);
     nn_xpack_free (xp);
+    thread_state_asleep (lookup_thread_state ());
   }
 
   assert (ddsrt_avl_is_empty (&evq->msg_xevents));