[event_engine/promises] Eliminate lock contention on call path for GetDefaultEventEngine (#31405)

* [event_engine/promises] Eliminate lock contention on call path for GetDefaultEventEngine

* crash fix

* fix

src/core/lib/channel/promise_based_filter.cc

@@ -25,7 +25,6 @@
 #include <grpc/status.h>
 
 #include "src/core/lib/channel/channel_stack.h"
-#include "src/core/lib/event_engine/default_event_engine.h"
 #include "src/core/lib/gprpp/manual_constructor.h"
 #include "src/core/lib/gprpp/status_helper.h"
 #include "src/core/lib/iomgr/error.h"
@@ -45,7 +44,9 @@ BaseCallData::BaseCallData(grpc_call_element* elem,
       call_combiner_(args->call_combiner),
       deadline_(args->deadline),
       context_(args->context),
-      event_engine_(grpc_event_engine::experimental::GetDefaultEventEngine()) {
+      event_engine_(
+          static_cast<ChannelFilter*>(elem->channel_data)
+              ->hack_until_per_channel_stack_event_engines_land_get_event_engine()) {
   if (flags & kFilterExaminesServerInitialMetadata) {
     server_initial_metadata_latch_ = arena_->New<Latch<ServerMetadata*>>();
   }

src/core/lib/channel/promise_based_filter.h

@@ -108,6 +108,16 @@ class ChannelFilter {
   virtual bool GetChannelInfo(const grpc_channel_info*) { return false; }
 
   virtual ~ChannelFilter() = default;
+
+  grpc_event_engine::experimental::EventEngine*
+  hack_until_per_channel_stack_event_engines_land_get_event_engine() {
+    return event_engine_.get();
+  }
+
+ private:
+  // TODO(ctiller): remove once per-channel-stack event engines land
+  std::shared_ptr<grpc_event_engine::experimental::EventEngine> event_engine_ =
+      grpc_event_engine::experimental::GetDefaultEventEngine();
 };
 
 // Designator for whether a filter is client side or server side.
@@ -176,7 +186,7 @@ class BaseCallData : public Activity, private Wakeable {
               call_data->pollent_.load(std::memory_order_acquire)),
           promise_detail::Context<CallFinalization>(&call_data->finalization_),
           promise_detail::Context<grpc_event_engine::experimental::EventEngine>(
-              call_data->event_engine_.get()) {}
+              call_data->event_engine_) {}
   };
 
   class Flusher {
@@ -283,7 +293,7 @@ class BaseCallData : public Activity, private Wakeable {
   grpc_call_context_element* const context_;
   std::atomic<grpc_polling_entity*> pollent_{nullptr};
   Latch<ServerMetadata*>* server_initial_metadata_latch_ = nullptr;
-  std::shared_ptr<grpc_event_engine::experimental::EventEngine> event_engine_;
+  grpc_event_engine::experimental::EventEngine* event_engine_;
 };
 
 class ClientCallData : public BaseCallData {

test/core/filters/client_authority_filter_test.cc

@@ -127,5 +127,10 @@ TEST(ClientAuthorityFilterTest,
 
 int main(int argc, char** argv) {
   ::testing::InitGoogleTest(&argc, argv);
-  return RUN_ALL_TESTS();
+  // TODO(ctiller): promise_based_call currently demands to instantiate an event
+  // engine which needs grpc to be initialized.
+  grpc_init();
+  int r = RUN_ALL_TESTS();
+  grpc_shutdown();
+  return r;
 }