[SYCL][L0] Fix interop event leak

sycl/plugins/level_zero/pi_level_zero.cpp

@@ -5443,7 +5443,17 @@ pi_result piextEventCreateWithNativeHandle(pi_native_handle NativeHandle,
   // Assume native event is host-visible, or otherwise we'd
   // need to create a host-visible proxy for it.
   (*Event)->HostVisibleEvent = *Event;
-
+  // A regular pi_event created by piEventCreate() starts with its reference
+  // count = 2 because of our explicit call to piEventCreate() at the end of
+  // createEventAndAssociateQueue().
+  // Then, this ref count becomes zero when the event is completed and RT
+  // calls piEventRelease().
+  // However, an interop event created in this function would go through
+  // the same life cycle, meaning it will be released only twice when RT
+  // calls piEventRelease in the sycl::event_impl destructor and when
+  // the Queue associated with the event is released.
+  // So, we increase the ref count of the interop pi_event here.
+  PI_CALL(piEventRetain(*Event));
   return PI_SUCCESS;
 }
 

sycl/source/detail/event_impl.cpp

@@ -123,8 +123,9 @@ event_impl::event_impl(RT::PiEvent Event, const context &SyclContext)
         "clEvent.",
         PI_INVALID_CONTEXT);
   }
-
-  getPlugin().call<PiApiKind::piEventRetain>(MEvent);
+  // Ref count should be incremented for OpenCL backend only.
+  if (getPlugin().getBackend() == cl::sycl::backend::opencl)
+    getPlugin().call<PiApiKind::piEventRetain>(MEvent);
 }
 
 event_impl::event_impl(const QueueImplPtr &Queue)