[SYCL][Docs] Make external events wait with queue

sycl/doc/extensions/experimental/sycl_ext_oneapi_in_order_queue_events.asciidoc

@@ -140,6 +140,11 @@ This is equivalent to calling `handler::depends_on()` in a command submission
 with the `externalEvent` from the most recent call to this member function since
 the previous command submission to the same queue.
 
+If `queue::wait()` or `queue::wait_and_throw()` is called prior to any command
+submission following a call to this member function, `externalEvent.wait()` is
+called and `externalEvent` will not be a dependency on the next command
+submitted to the queue.
+
 Calls to this member function throw a `sycl::exception` with `errc::invalid` if
 the queue does not have the `property::queue::in_order` property.
 

sycl/source/detail/queue_impl.cpp

@@ -516,6 +516,11 @@ void queue_impl::wait(const detail::code_location &CodeLoc) {
   for (const EventImplPtr &Event : StreamsServiceEvents)
     Event->wait(Event);
 
+  // If there is an external event set, we need to wait on it.
+  std::optional<event> ExternalEvent = popExternalEvent();
+  if (ExternalEvent)
+    ExternalEvent->wait();
+
 #ifdef XPTI_ENABLE_INSTRUMENTATION
   instrumentationEpilog(TelemetryEvent, Name, StreamID, IId);
 #endif

sycl/test-e2e/InOrderEventsExt/set_external_event.cpp

@@ -8,16 +8,13 @@
 
 constexpr size_t N = 1024;
 
-int main() {
-  sycl::context Ctx;
-  sycl::device Dev = Ctx.get_devices()[0];
-
-  sycl::queue Q1{Ctx, Dev, {sycl::property::queue::in_order{}}};
-  sycl::queue Q2{Ctx, Dev, {sycl::property::queue::in_order{}}};
+int check_work(sycl::queue &Q1, sycl::queue &Q2) {
+  std::cout << "Checking ext_oneapi_set_external_event for a workload."
+            << std::endl;
 
   sycl::buffer<int> DevDataBuf{sycl::range{N}};
   sycl::accessor DevData{DevDataBuf};
-  int *HostData = (int *)malloc(N * sizeof(int) * 10);
+  int *HostData = new int[N * 10];
 
   for (size_t I = 0; I < 10; ++I) {
     Q1.fill(DevData, 0);
@@ -52,6 +49,55 @@ int main() {
       }
     }
   }
-  free(HostData);
+  delete[] HostData;
+  return Failures;
+}
+
+int check_wait(sycl::queue &Q1, sycl::queue &Q2) {
+  std::cout << "Checking ext_oneapi_set_external_event with wait on queue."
+            << std::endl;
+
+  sycl::buffer<int> DevDataBuf{sycl::range{N}};
+  sycl::accessor DevData{DevDataBuf};
+  int *HostData = new int[N];
+
+  Q1.fill(DevData, 0);
+  for (size_t I = 0; I < 10; ++I) {
+    Q1.submit([&](sycl::handler &h) {
+      h.require(DevData);
+      h.parallel_for(N, [=](sycl::item<1> Idx) { ++DevData[Idx]; });
+    });
+  }
+  sycl::event E = Q1.copy(DevData, HostData);
+
+  Q2.ext_oneapi_set_external_event(E);
+  Q2.wait_and_throw();
+
+  int Failures = 0;
+  for (size_t I = 0; I < N; ++I) {
+    int Expected = 10;
+    int Actual = HostData[I];
+    if (Expected != Actual) {
+      std::cout << "Result not matching the expected value at index " << I
+                << ": " << Expected << " != " << Actual << std::endl;
+      ++Failures;
+    }
+  }
+  delete[] HostData;
+  return Failures;
+}
+
+int main() {
+  sycl::context Ctx;
+  sycl::device Dev = Ctx.get_devices()[0];
+
+  sycl::queue Q1{Ctx, Dev, {sycl::property::queue::in_order{}}};
+  sycl::queue Q2{Ctx, Dev, {sycl::property::queue::in_order{}}};
+
+  int Failures = 0;
+
+  Failures += check_work(Q1, Q2);
+  Failures += check_wait(Q1, Q2);
+
   return Failures;
 }