1 files changed, 25 insertions, 11 deletions

diff --git a/src/cpp/server/server_cc.cc b/src/cpp/server/server_cc.cc
index 7c764f4bce..7aeddff643 100644
--- a/src/cpp/server/server_cc.cc
+++ b/src/cpp/server/server_cc.cc
@@ -380,7 +380,6 @@ class Server::SyncRequestThreadManager : public ThreadManager {
   int cq_timeout_msec_;
   std::vector<std::unique_ptr<SyncRequest>> sync_requests_;
   std::unique_ptr<internal::RpcServiceMethod> unknown_method_;
-  std::unique_ptr<internal::RpcServiceMethod> health_check_;
   std::shared_ptr<Server::GlobalCallbacks> global_callbacks_;
 };
 
@@ -573,16 +572,24 @@ void Server::Start(ServerCompletionQueue** cqs, size_t num_cqs) {
 
   // Only create default health check service when user did not provide an
   // explicit one.
+  ServerCompletionQueue* health_check_cq = nullptr;
+  DefaultHealthCheckService::HealthCheckServiceImpl*
+      default_health_check_service_impl = nullptr;
   if (health_check_service_ == nullptr && !health_check_service_disabled_ &&
       DefaultHealthCheckServiceEnabled()) {
-    if (sync_server_cqs_ == nullptr || sync_server_cqs_->empty()) {
-      gpr_log(GPR_INFO,
-              "Default health check service disabled at async-only server.");
-    } else {
-      auto* default_hc_service = new DefaultHealthCheckService;
-      health_check_service_.reset(default_hc_service);
-      RegisterService(nullptr, default_hc_service->GetHealthCheckService());
-    }
+    auto* default_hc_service = new DefaultHealthCheckService;
+    health_check_service_.reset(default_hc_service);
+    // We create a non-polling CQ to avoid impacting application
+    // performance.  This ensures that we don't introduce thread hops
+    // for application requests that wind up on this CQ, which is polled
+    // in its own thread.
+    health_check_cq = new ServerCompletionQueue(GRPC_CQ_NON_POLLING);
+    grpc_server_register_completion_queue(server_, health_check_cq->cq(),
+                                          nullptr);
+    default_health_check_service_impl =
+        default_hc_service->GetHealthCheckService(
+            std::unique_ptr<ServerCompletionQueue>(health_check_cq));
+    RegisterService(nullptr, default_health_check_service_impl);
   }
 
   grpc_server_start(server_);
@@ -597,6 +604,9 @@ void Server::Start(ServerCompletionQueue** cqs, size_t num_cqs) {
         new UnimplementedAsyncRequest(this, cqs[i]);
       }
     }
+    if (health_check_cq != nullptr) {
+      new UnimplementedAsyncRequest(this, health_check_cq);
+    }
   }
 
   // If this server has any support for synchronous methods (has any sync
@@ -609,6 +619,10 @@ void Server::Start(ServerCompletionQueue** cqs, size_t num_cqs) {
   for (auto it = sync_req_mgrs_.begin(); it != sync_req_mgrs_.end(); it++) {
     (*it)->Start();
   }
+
+  if (default_health_check_service_impl != nullptr) {
+    default_health_check_service_impl->StartServingThread();
+  }
 }
 
 void Server::ShutdownInternal(gpr_timespec deadline) {
@@ -671,8 +685,8 @@ void Server::PerformOpsOnCall(internal::CallOpSetInterface* ops,
   size_t nops = 0;
   grpc_op cops[MAX_OPS];
   ops->FillOps(call->call(), cops, &nops);
-  // TODO(vjpai): Use ops->cq_tag once this case supports callbacks
-  auto result = grpc_call_start_batch(call->call(), cops, nops, ops, nullptr);
+  auto result =
+      grpc_call_start_batch(call->call(), cops, nops, ops->cq_tag(), nullptr);
   if (result != GRPC_CALL_OK) {
     gpr_log(GPR_ERROR, "Fatal: grpc_call_start_batch returned %d", result);
     grpc_call_log_batch(__FILE__, __LINE__, GPR_LOG_SEVERITY_ERROR,