Implement shared ExecutionContext for handlers. (#716)

[RFC=0002](https://github.com/googlecartographer/rfcs/blob/master/text/0002-cloud-based-mapping-1.md)

cartographer_grpc/framework/execution_context.h

@@ -0,0 +1,61 @@
+/*
+ * Copyright 2017 The Cartographer Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CARTOGRAPHER_GRPC_FRAMEWORK_EXECUTION_CONTEXT_H
+#define CARTOGRAPHER_GRPC_FRAMEWORK_EXECUTION_CONTEXT_H
+
+#include "cartographer/common/mutex.h"
+#include "glog/logging.h"
+
+namespace cartographer_grpc {
+namespace framework {
+
+// Implementations of this class allow RPC handlers to share state among one
+// another. Using Server::SetExecutionContext(...) a server-wide
+// 'ExecutionContext' can be specified. This 'ExecutionContext' can be retrieved
+// by all implementations of 'RpcHandler' by calling
+// 'RpcHandler::GetContext<MyContext>()'.
+class ExecutionContext {
+ public:
+  // This non-movable, non-copyable class is used to broker access from various
+  // RPC handlers to the shared 'ExecutionContext'. Handles automatically lock
+  // the context they point to.
+  template <typename ContextType>
+  class Synchronized {
+   public:
+    ContextType* operator->() {
+      return static_cast<ContextType*>(execution_context_);
+    }
+    Synchronized(cartographer::common::Mutex* lock,
+                 ExecutionContext* execution_context)
+        : locker_(lock), execution_context_(execution_context) {}
+    Synchronized(const Synchronized&) = delete;
+    Synchronized(Synchronized&&) = delete;
+
+   private:
+    cartographer::common::MutexLocker locker_;
+    ExecutionContext* execution_context_;
+  };
+  cartographer::common::Mutex* lock() { return &lock_; }
+
+ private:
+  cartographer::common::Mutex lock_;
+};
+
+}  // namespace framework
+}  // namespace cartographer_grpc
+
+#endif  // CARTOGRAPHER_GRPC_FRAMEWORK_EXECUTION_CONTEXT_H

cartographer_grpc/framework/rpc.cc

@@ -25,16 +25,18 @@ namespace framework {
 
 Rpc::Rpc(int method_index,
          ::grpc::ServerCompletionQueue* server_completion_queue,
+         ExecutionContext* execution_context,
          const RpcHandlerInfo& rpc_handler_info, Service* service)
     : method_index_(method_index),
       server_completion_queue_(server_completion_queue),
+      execution_context_(execution_context),
       rpc_handler_info_(rpc_handler_info),
       service_(service),
       new_connection_event_{Event::NEW_CONNECTION, this, false},
       read_event_{Event::READ, this, false},
       write_event_{Event::WRITE, this, false},
       done_event_{Event::DONE, this, false},
-      handler_(rpc_handler_info_.rpc_handler_factory(this)) {
+      handler_(rpc_handler_info_.rpc_handler_factory(this, execution_context)) {
   InitializeReadersAndWriters(rpc_handler_info_.rpc_type);
 
   // Initialize the prototypical request and response messages.
@@ -48,7 +50,8 @@ Rpc::Rpc(int method_index,
 
 std::unique_ptr<Rpc> Rpc::Clone() {
   return cartographer::common::make_unique<Rpc>(
-      method_index_, server_completion_queue_, rpc_handler_info_, service_);
+      method_index_, server_completion_queue_, execution_context_,
+      rpc_handler_info_, service_);
 }
 
 void Rpc::OnRequest() { handler_->OnRequestInternal(request_.get()); }

cartographer_grpc/framework/rpc.h

@@ -21,6 +21,7 @@
 #include <unordered_set>
 
 #include "cartographer/common/mutex.h"
+#include "cartographer_grpc/framework/execution_context.h"
 #include "cartographer_grpc/framework/rpc_handler_interface.h"
 #include "google/protobuf/message.h"
 #include "grpc++/grpc++.h"
@@ -47,6 +48,7 @@ class Rpc {
   };
 
   Rpc(int method_index, ::grpc::ServerCompletionQueue* server_completion_queue,
+      ExecutionContext* execution_context,
       const RpcHandlerInfo& rpc_handler_info, Service* service);
   std::unique_ptr<Rpc> Clone();
   void OnRequest();
@@ -69,6 +71,7 @@ class Rpc {
 
   int method_index_;
   ::grpc::ServerCompletionQueue* server_completion_queue_;
+  ExecutionContext* execution_context_;
   RpcHandlerInfo rpc_handler_info_;
   Service* service_;
   ::grpc::ServerContext server_context_;

cartographer_grpc/framework/rpc_handler.h

@@ -17,6 +17,7 @@
 #ifndef CARTOGRAPHER_GRPC_FRAMEWORK_RPC_HANDLER_H
 #define CARTOGRAPHER_GRPC_FRAMEWORK_RPC_HANDLER_H
 
+#include "cartographer_grpc/framework/execution_context.h"
 #include "cartographer_grpc/framework/rpc.h"
 #include "cartographer_grpc/framework/rpc_handler_interface.h"
 #include "cartographer_grpc/framework/type_traits.h"
@@ -35,6 +36,9 @@ class RpcHandler : public RpcHandlerInterface {
   using RequestType = StripStream<Incoming>;
   using ResponseType = StripStream<Outgoing>;
 
+  void SetExecutionContext(ExecutionContext* execution_context) {
+    execution_context_ = execution_context;
+  }
   void SetRpc(Rpc* rpc) override { rpc_ = rpc; }
   void OnRequestInternal(const ::google::protobuf::Message* request) override {
     DCHECK(dynamic_cast<const RequestType*>(request));
@@ -44,9 +48,14 @@ class RpcHandler : public RpcHandlerInterface {
   void Send(std::unique_ptr<ResponseType> response) {
     rpc_->Write(std::move(response));
   }
+  template <typename T>
+  ExecutionContext::Synchronized<T> GetContext() {
+    return {execution_context_->lock(), execution_context_};
+  }
 
  private:
   Rpc* rpc_;
+  ExecutionContext* execution_context_;
 };
 
 }  // namespace framework

cartographer_grpc/framework/rpc_handler_interface.h

@@ -17,6 +17,7 @@
 #ifndef CARTOGRAPHER_GRPC_FRAMEWORK_RPC_HANDLER_INTERFACE_H_H
 #define CARTOGRAPHER_GRPC_FRAMEWORK_RPC_HANDLER_INTERFACE_H_H
 
+#include "cartographer_grpc/framework/execution_context.h"
 #include "google/protobuf/message.h"
 #include "grpc++/grpc++.h"
 
@@ -27,14 +28,15 @@ class Rpc;
 class RpcHandlerInterface {
  public:
   virtual ~RpcHandlerInterface() = default;
+  virtual void SetExecutionContext(ExecutionContext* execution_context) = 0;
   virtual void SetRpc(Rpc* rpc) = 0;
   virtual void OnRequestInternal(
       const ::google::protobuf::Message* request) = 0;
   virtual void OnReadsDone() = 0;
 };
 
-using RpcHandlerFactory =
-    std::function<std::unique_ptr<RpcHandlerInterface>(Rpc*)>;
+using RpcHandlerFactory = std::function<std::unique_ptr<RpcHandlerInterface>(
+    Rpc*, ExecutionContext*)>;
 
 struct RpcHandlerInfo {
   const google::protobuf::Descriptor* request_descriptor;

cartographer_grpc/framework/server.cc

@@ -77,7 +77,8 @@ void Server::Start() {
 
   // Start serving all services on all completion queues.
   for (auto& service : services_) {
-    service.second.StartServing(completion_queue_threads_);
+    service.second.StartServing(completion_queue_threads_,
+                                execution_context_.get());
   }
 
   // Start threads to process all completion queues.
@@ -107,5 +108,13 @@ void Server::Shutdown() {
   LOG(INFO) << "Shutdown complete.";
 }
 
+void Server::SetExecutionContext(
+    std::unique_ptr<ExecutionContext> execution_context) {
+  // After the server has been started the 'ExecutionHandle' cannot be changed
+  // anymore.
+  CHECK(!server_);
+  execution_context_ = std::move(execution_context);
+}
+
 }  // namespace framework
 }  // namespace cartographer_grpc

cartographer_grpc/framework/server.h

@@ -24,6 +24,7 @@
 
 #include "cartographer/common/make_unique.h"
 #include "cartographer_grpc/framework/completion_queue_thread.h"
+#include "cartographer_grpc/framework/execution_context.h"
 #include "cartographer_grpc/framework/rpc_handler.h"
 #include "cartographer_grpc/framework/service.h"
 #include "grpc++/grpc++.h"
@@ -57,10 +58,11 @@ class Server {
           RpcHandlerInfo{
               RpcHandlerType::RequestType::default_instance().GetDescriptor(),
               RpcHandlerType::ResponseType::default_instance().GetDescriptor(),
-              [](Rpc* const rpc) {
+              [](Rpc* const rpc, ExecutionContext* const execution_context) {
                 std::unique_ptr<RpcHandlerInterface> rpc_handler =
                     cartographer::common::make_unique<RpcHandlerType>();
                 rpc_handler->SetRpc(rpc);
+                rpc_handler->SetExecutionContext(execution_context);
                 return rpc_handler;
               },
               RpcType<typename RpcHandlerType::IncomingType,
@@ -81,6 +83,9 @@ class Server {
   // Shuts down the server and all of its services.
   void Shutdown();
 
+  // Sets the server-wide context object shared between RPC handlers.
+  void SetExecutionContext(std::unique_ptr<ExecutionContext> execution_context);
+
  private:
   Server(const Options& options);
   Server(const Server&) = delete;
@@ -104,6 +109,10 @@ class Server {
 
   // Map of service names to services.
   std::map<std::string, Service> services_;
+
+  // A context object that is shared between all implementations of
+  // 'RpcHandler'.
+  std::unique_ptr<ExecutionContext> execution_context_;
 };
 
 }  // namespace framework

cartographer_grpc/framework/server_test.cc

@@ -16,6 +16,7 @@
 
 #include "cartographer_grpc/framework/server.h"
 
+#include "cartographer_grpc/framework/execution_context.h"
 #include "cartographer_grpc/framework/proto/math_service.grpc.pb.h"
 #include "cartographer_grpc/framework/proto/math_service.pb.h"
 #include "cartographer_grpc/framework/rpc_handler.h"
@@ -27,10 +28,16 @@ namespace cartographer_grpc {
 namespace framework {
 namespace {
 
+class MathServerContext : public ExecutionContext {
+ public:
+  int additional_increment() { return 10; }
+};
+
 class GetServerOptionsHandler
     : public RpcHandler<Stream<proto::GetSumRequest>, proto::GetSumResponse> {
  public:
   void OnRequest(const proto::GetSumRequest& request) override {
+    sum_ += GetContext<MathServerContext>()->additional_increment();
     sum_ += request.input();
   }
 
@@ -70,6 +77,8 @@ TEST_F(ServerTest, StartAndStopServerTest) {
 }
 
 TEST_F(ServerTest, ProcessRpcStreamTest) {
+  server_->SetExecutionContext(
+      cartographer::common::make_unique<MathServerContext>());
   server_->Start();
 
   auto channel =
@@ -87,7 +96,7 @@ TEST_F(ServerTest, ProcessRpcStreamTest) {
   writer->WritesDone();
   grpc::Status status = writer->Finish();
   EXPECT_TRUE(status.ok());
-  EXPECT_EQ(result.output(), 3);
+  EXPECT_EQ(result.output(), 33);
 
   server_->Shutdown();
 }

cartographer_grpc/framework/service.cc

@@ -37,12 +37,13 @@ Service::Service(const std::string& service_name,
 }
 
 void Service::StartServing(
-    std::vector<CompletionQueueThread>& completion_queue_threads) {
+    std::vector<CompletionQueueThread>& completion_queue_threads,
+    ExecutionContext* execution_context) {
   int i = 0;
   for (const auto& rpc_handler_info : rpc_handler_infos_) {
     for (auto& completion_queue_thread : completion_queue_threads) {
       Rpc* rpc = active_rpcs_.Add(cartographer::common::make_unique<Rpc>(
-          i, completion_queue_thread.completion_queue(),
+          i, completion_queue_thread.completion_queue(), execution_context,
           rpc_handler_info.second, this));
       rpc->RequestNextMethodInvocation();
     }

cartographer_grpc/framework/service.h

@@ -18,6 +18,7 @@
 #define CARTOGRAPHER_GRPC_FRAMEWORK_SERVICE_H
 
 #include "cartographer_grpc/framework/completion_queue_thread.h"
+#include "cartographer_grpc/framework/execution_context.h"
 #include "cartographer_grpc/framework/rpc.h"
 #include "cartographer_grpc/framework/rpc_handler.h"
 #include "grpc++/impl/codegen/service_type.h"
@@ -35,7 +36,8 @@ class Service : public ::grpc::Service {
 
   Service(const std::string& service_name,
           const std::map<std::string, RpcHandlerInfo>& rpc_handlers);
-  void StartServing(std::vector<CompletionQueueThread>& completion_queues);
+  void StartServing(std::vector<CompletionQueueThread>& completion_queues,
+                    ExecutionContext* execution_context);
   void HandleEvent(Rpc::Event event, Rpc* rpc, bool ok);
   void StopServing();