[service] Add a CompilationSession abstract base class.

The CompilationSession class encapsulates an incremental compilation
session.

This is the first in a series of patches that separates the RPC server
from the compilation session.

Issue #254.

compiler_gym/service/BUILD

@@ -3,6 +3,7 @@
 # This source code is licensed under the MIT license found in the
 # LICENSE file in the root directory of this source tree.
 load("@rules_python//python:defs.bzl", "py_library")
+load("@rules_cc//cc:defs.bzl", "cc_library")
 
 py_library(
     name = "service",
@@ -15,6 +16,18 @@ py_library(
     ],
 )
 
+cc_library(
+    name = "CompilationSession",
+    srcs = ["CompilationSession.cc"],
+    hdrs = ["CompilationSession.h"],
+    visibility = ["//visibility:public"],
+    deps = [
+        "//compiler_gym/service/proto:compiler_gym_service_cc",
+        "@boost//:filesystem",
+        "@com_github_grpc_grpc//:grpc++",
+    ],
+)
+
 py_library(
     name = "connection",
     srcs = ["connection.py"],

compiler_gym/service/CompilationSession.cc

@@ -0,0 +1,26 @@
+// Copyright (c) Facebook, Inc. and its affiliates.
+//
+// This source code is licensed under the MIT license found in the
+// LICENSE file in the root directory of this source tree.
+#include "compiler_gym/service/CompilationSession.h"
+
+using grpc::Status;
+using grpc::StatusCode;
+
+namespace compiler_gym {
+
+std::string CompilationSession::getCompilerVersion() const { return ""; }
+
+Status CompilationSession::init(CompilationSession& other) {
+  return Status(StatusCode::UNIMPLEMENTED, "CompilationSession::init() not implemented");
+}
+
+Status CompilationSession::endOfStep(bool& endOfEpisode,
+                                     std::optional<ActionSpace>& newActionSpace) {
+  return Status::OK;
+}
+
+CompilationSession::CompilationSession(const boost::filesystem::path& workingDirectory)
+    : workingDirectory_(workingDirectory) {}
+
+}  // namespace compiler_gym

compiler_gym/service/CompilationSession.h

@@ -0,0 +1,71 @@
+// Copyright (c) Facebook, Inc. and its affiliates.
+//
+// This source code is licensed under the MIT license found in the
+// LICENSE file in the root directory of this source tree.
+#pragma once
+
+#include <grpcpp/grpcpp.h>
+
+#include <vector>
+
+#include "boost/filesystem.hpp"
+#include "compiler_gym/service/proto/compiler_gym_service.pb.h"
+
+namespace compiler_gym {
+
+// Base class for encapsulating an incremental compilation session.
+//
+// To add support for a new compiler, suclass from this base and provide
+// implementations of the abstract methods.
+class CompilationSession {
+ public:
+  // Get the compiler version.
+  virtual std::string getCompilerVersion() const;
+
+  // A list of action spaces describing the capabilities of the compiler.
+  virtual std::vector<ActionSpace> getActionSpaces() const = 0;
+
+  // A list of feature vectors that this compiler provides.
+  virtual std::vector<ObservationSpace> getObservationSpaces() const = 0;
+
+  // Start a CompilationSession. This will be called after construction and
+  // before applyAction() or computeObservation(). This will only be called
+  // once.
+  [[nodiscard]] virtual grpc::Status init(const ActionSpace& actionSpace,
+                                          const Benchmark& benchmark) = 0;
+
+  // Initialize the state from another CompilerSession. This will be called
+  // after construction and before applyAction() or computeObservation(). This
+  // will only be called once.
+  [[nodiscard]] virtual grpc::Status init(CompilationSession& other);
+
+  // Apply an action.
+  [[nodiscard]] virtual grpc::Status applyAction(const Action& action, bool& endOfEpisode,
+                                                 std::optional<ActionSpace>& newActionSpace,
+                                                 bool& actionHadNoEffect) = 0;
+
+  // compute an observation
+  [[nodiscard]] virtual grpc::Status computeObservation(const ObservationSpace& observationSpace,
+                                                        Observation& observation) = 0;
+
+  // Optional. This will be called after all applyAction() and
+  // computeObservation() in a step. Use this method if you would like to
+  // perform post-transform validation of compiler state.
+  [[nodiscard]] virtual grpc::Status endOfStep(bool actionHadNoEffect, bool& endOfEpisode,
+                                               std::optional<ActionSpace>& newActionSpace);
+
+ protected:
+  // Get the working directory, which is a local filesystem directory that this
+  // CompilationSession can use to store temporary files such as build
+  // artifacts.
+  inline const boost::filesystem::path& workingDirectory() { return workingDirectory_; }
+
+  CompilationSession(const boost::filesystem::path& workingDirectory);
+
+  virtual ~CompilationSession() = default;
+
+ private:
+  const boost::filesystem::path workingDirectory_;
+};
+
+}  // namespace compiler_gym