Restore lock and rework test

Author: igchor

sycl/source/detail/queue_impl.cpp

@@ -349,7 +349,13 @@ queue_impl::submit_impl(const detail::type_erased_cgfo_ty &CGF,
                          !requiresPostProcess;
 
   if (noLastEventPath) {
-    return finalizeHandlerInOrderNoEventsUnlocked(Handler);
+    std::unique_lock<std::mutex> Lock(MMutex);
+
+    // Check if we are still in no last event mode. There could
+    // have been a concurrent submit.
+    if (MNoLastEventMode.load(std::memory_order_relaxed)) {
+      return finalizeHandlerInOrderNoEventsUnlocked(Handler);
+    }
   }
 
   detail::EventImplPtr EventImpl;

sycl/source/detail/queue_impl.hpp

@@ -754,7 +754,7 @@ class queue_impl : public std::enable_shared_from_this<queue_impl> {
 
     if (Event && !Scheduler::CheckEventReadiness(MContext, Event)) {
       MDefaultGraphDeps.LastEventPtr = Event;
-      MNoLastEventMode = false;
+      MNoLastEventMode.store(false, std::memory_order_relaxed);
     }
 
     return Event;

sycl/test-e2e/InorderQueue/in_order_multi_queue_host_task.cpp

@@ -7,6 +7,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
+#include <condition_variable>
 #include <iostream>
 
 #include <sycl/detail/core.hpp>
@@ -15,7 +16,7 @@
 
 using namespace sycl;
 
-const int dataSize = 1024 * 1024;
+const int dataSize = 1024;
 
 int main() {
   queue Queue1{property::queue::in_order()};
@@ -25,8 +26,14 @@ int main() {
   int *dataB = malloc_host<int>(dataSize, Queue1);
   int *dataC = malloc_host<int>(dataSize, Queue1);
 
+  bool ready = false;
+  std::mutex host_task_mtx;
+  std::condition_variable cv;
+
   auto Event1 = Queue1.submit([&](handler &cgh) {
     cgh.host_task([&] {
+      std::unique_lock<std::mutex> lk(host_task_mtx);
+      cv.wait(lk, [&] { return ready; });
       for (size_t i = 0; i < dataSize; ++i) {
         dataA[i] = i;
       }
@@ -39,6 +46,12 @@ int main() {
                      [=](id<1> idx) { dataB[idx[0]] = dataA[idx[0]]; });
   });
 
+  {
+    std::unique_lock<std::mutex> lk(host_task_mtx);
+    ready = true;
+  }
+  cv.notify_one();
+
   Queue2.wait();
 
   for (size_t i = 0; i != dataSize; ++i) {