[SYCL] Fix memory leak (queue_impl) due to #5901

sycl/source/detail/event_impl.hpp

@@ -214,8 +214,16 @@ class event_impl {
 
   /// Returns worker queue for command.
   ///
-  /// @return a reference to MWorkerQueue.
-  QueueImplPtr &getWorkerQueue() { return MWorkerQueue; };
+  /// @return shared_ptr to MWorkerQueue, please be aware it can be empty
+  /// pointer
+  QueueImplPtr getWorkerQueue() { return MWorkerQueue.lock(); };
+
+  /// Sets worker queue for command.
+  ///
+  /// @return
+  void setWorkerQueue(const QueueImplPtr &WorkerQueue) {
+    MWorkerQueue = WorkerQueue;
+  };
 
   /// Checks if an event is in a fully intialized state. Default-constructed
   /// events will return true only after having initialized its native event,
@@ -248,7 +256,7 @@ class event_impl {
   std::weak_ptr<queue_impl> MQueue;
   const bool MIsProfilingEnabled = false;
 
-  QueueImplPtr MWorkerQueue;
+  std::weak_ptr<queue_impl> MWorkerQueue;
 
   /// Dependency events prepared for waiting by backend.
   std::vector<EventImplPtr> MPreparedDepsEvents;

sycl/source/detail/scheduler/commands.cpp

@@ -214,6 +214,8 @@ Command::getPiEvents(const std::vector<EventImplPtr> &EventImpls) const {
     // current one is a host task. In this case we should not skip pi event due
     // to different sync mechanisms for different task types on in-order queue.
     const QueueImplPtr &WorkerQueue = getWorkerQueue();
+    // MWorkerQueue in command is always not null. So check if
+    // EventImpl->getWorkerQueue != nullptr is implicit.
     if (EventImpl->getWorkerQueue() == WorkerQueue &&
         WorkerQueue->isInOrder() && !isHostTask())
       continue;
@@ -410,12 +412,12 @@ void Command::waitForEvents(QueueImplPtr Queue,
 Command::Command(CommandType Type, QueueImplPtr Queue)
     : MQueue(std::move(Queue)),
       MEvent(std::make_shared<detail::event_impl>(MQueue)),
-      MWorkerQueue(MEvent->getWorkerQueue()),
       MPreparedDepsEvents(MEvent->getPreparedDepsEvents()),
       MPreparedHostDepsEvents(MEvent->getPreparedHostDepsEvents()),
       MType(Type) {
   MSubmittedQueue = MQueue;
   MWorkerQueue = MQueue;
+  MEvent->setWorkerQueue(MWorkerQueue);
   MEvent->setCommand(this);
   MEvent->setContextImpl(MQueue->getContextImplPtr());
   MEvent->setStateIncomplete();
@@ -1313,6 +1315,7 @@ MemCpyCommand::MemCpyCommand(Requirement SrcReq,
   }
 
   MWorkerQueue = MQueue->is_host() ? MSrcQueue : MQueue;
+  MEvent->setWorkerQueue(MWorkerQueue);
 
   emitInstrumentationDataProxy();
 }
@@ -1494,6 +1497,7 @@ MemCpyCommandHost::MemCpyCommandHost(Requirement SrcReq,
   }
 
   MWorkerQueue = MQueue->is_host() ? MSrcQueue : MQueue;
+  MEvent->setWorkerQueue(MWorkerQueue);
 
   emitInstrumentationDataProxy();
 }

sycl/source/detail/scheduler/commands.hpp

@@ -218,8 +218,7 @@ class Command {
   QueueImplPtr MQueue;
   QueueImplPtr MSubmittedQueue;
   EventImplPtr MEvent;
-
-  QueueImplPtr &MWorkerQueue;
+  QueueImplPtr MWorkerQueue;
 
   /// Dependency events prepared for waiting by backend.
   /// See processDepEvent for details.