[SYCL] Filter out empty events for the barrier with waitlist (#12951)

Fix for #12177
Now even if the waitlist consists of only empty events we still invoke
the scheduler to submit barrier command. Scheduler creates sycl event
with associated Barrier Command but doesn't actually enqueue a barrier
because waitlist is empty (consists of only empty events). As a result,
the event returned by such barrier doesn't have PI handle but it
supposed to have. If such event is then passed to some another command
later as a dependency then it leads to nullptr dereference.

So, filter out such events from waitlist to avoid going to sheduler in
such scenarios.

Test provided by Andrey Alekseenko <[email protected]>
Co-authored-by:  Andrey Alekseenko <[email protected]>

Author: againull

sycl/source/queue.cpp

@@ -238,7 +238,11 @@ event queue::ext_oneapi_submit_barrier(const detail::code_location &CodeLoc) {
 /// group is being enqueued on.
 event queue::ext_oneapi_submit_barrier(const std::vector<event> &WaitList,
                                        const detail::code_location &CodeLoc) {
-  if (is_in_order() && WaitList.empty()) {
+  bool AllEventsEmpty = std::all_of(
+      begin(WaitList), end(WaitList), [&](const event &Event) -> bool {
+        return !detail::getSyclObjImpl(Event)->isContextInitialized();
+      });
+  if (is_in_order() && AllEventsEmpty) {
     // The last command recorded in the graph is not tracked by the queue but by
     // the graph itself. We must therefore search for the last node/event in the
     // graph.

sycl/test-e2e/Regression/ext_oneapi_barrier_opt.cpp

@@ -0,0 +1,45 @@
+// RUN: %{build} %threads_lib -o %t.out
+// RUN: %{run} %t.out
+
+// Check that ext_oneapi_submit_barrier works fine in the scenarios
+// when provided waitlist consists of only empty events.
+
+#include <iostream>
+#include <mutex>
+#include <sycl/sycl.hpp>
+#include <thread>
+
+static constexpr int niter = 1024;
+static constexpr int nthreads = 2;
+
+std::array<std::mutex, nthreads> mutexes;
+std::array<std::optional<sycl::event>, nthreads> events;
+
+void threadFunction(int tid) {
+  sycl::device dev;
+  std::cout << dev.get_info<sycl::info::device::name>() << std::endl;
+  sycl::context ctx{dev};
+  sycl::queue q1{ctx, dev, {sycl::property::queue::in_order()}};
+  sycl::queue q2{ctx, dev, {sycl::property::queue::in_order()}};
+  for (int i = 0; i < niter; i++) {
+    sycl::event ev1 = q1.ext_oneapi_submit_barrier();
+    q2.ext_oneapi_submit_barrier({ev1});
+    sycl::event ev2 = q2.ext_oneapi_submit_barrier();
+    q1.ext_oneapi_submit_barrier({ev2});
+  }
+}
+
+int main() {
+  std::array<std::thread, nthreads> threads;
+
+  for (int i = 0; i < nthreads; i++) {
+    threads[i] = std::thread{threadFunction, i};
+  }
+
+  for (int i = 0; i < nthreads; i++) {
+    threads[i].join();
+  }
+  std::cout << "All threads have finished." << std::endl;
+
+  return 0;
+}