Fix thread-safe destruction of cached events

Use a mutex to make the emptiness check and retrieval of cached events
atomic.

Author: Martin Wehking

source/adapters/cuda/queue.cpp

@@ -36,8 +36,10 @@ ur_queue_handle_t_::~ur_queue_handle_t_() {
   urContextRelease(Context);
   urDeviceRelease(Device);
 
-  while (has_cached_events()) {
-    get_cached_event();
+  std::lock_guard<std::mutex> CacheGuard(CacheMutex);
+  while (!CachedEvents.empty()) {
+    std::unique_ptr<ur_event_handle_t_> Ev{CachedEvents.top()};
+    CachedEvents.pop();
   }
 }
 

source/adapters/hip/event.cpp

@@ -297,7 +297,6 @@ UR_APIEXPORT ur_result_t UR_APICALL urEventRelease(ur_event_handle_t hEvent) {
   // decrement ref count. If it is 0, delete the event.
   if (hEvent->decrementReferenceCount() == 0) {
     std::unique_ptr<ur_event_handle_t_> event_ptr{hEvent};
-    ur_result_t Result = UR_RESULT_ERROR_INVALID_EVENT;
     try {
       if (!hEvent->backendHasOwnership()) {
         return UR_RESULT_SUCCESS;

source/adapters/hip/queue.cpp

@@ -32,8 +32,10 @@ ur_queue_handle_t_::~ur_queue_handle_t_() {
   urContextRelease(Context);
   urDeviceRelease(Device);
 
-  while (has_cached_events()) {
-    get_cached_event();
+  std::lock_guard<std::mutex> CacheGuard(CacheMutex);
+  while (!CachedEvents.empty()) {
+    std::unique_ptr<ur_event_handle_t_> Ev{CachedEvents.top()};
+    CachedEvents.pop();
   }
 }