[OPE] Improve IPC serialization of structs (#362)

This PR uses reflection to serialize structs instead of requiring us to define `ipc_serialize` and `ipc_deserialize` for every struct we want to pass to the worker process.

This is much less error prone than the manual method since adding a field to a struct no longer requires modifying serialization code.

As part of this, we switch to building Neuropod with C++17. We still build in a manylinux2014 compatible sysroot so we can't use all C++17 library features, but this lets us use some C++17 language features.

source/.bazelrc

@@ -7,8 +7,9 @@ build --test_env=VIRTUAL_ENV
 # Use an internal toolchain to isolate the build from system libraries
 build --crosstool_top=@llvm_toolchain//:toolchain
 
-# Use C++14
-build --cxxopt='-std=c++14'
+# Use some C++17 features. We still build in a C++14 sysroot so can't use all of them
+# (Linking will fail during linux builds if you're using a C++17 feature that isn't available)
+build --cxxopt='-std=c++17'
 
 # Build in a mostly-static way
 build --dynamic_mode off

source/WORKSPACE

@@ -183,3 +183,11 @@ http_archive(
     strip_prefix = "cpp-semver-ff341259099465283bc3dc60fb5ede16776e1607",
     url = "https://github.com/easz/cpp-semver/archive/ff341259099465283bc3dc60fb5ede16776e1607.zip",
 )
+
+http_archive(
+    name = "pfr_repo",
+    build_file = "@//deps:BUILD.pfr",
+    sha256 = "92e0ffa3be49ffb21486e8e929dde599455fc1818054254bac832bcbc2c5491b",
+    strip_prefix = "magic_get-1.0.0",
+    url = "https://github.com/apolukhin/magic_get/archive/1.0.0.zip",
+)

source/deps/BUILD.pfr

@@ -0,0 +1,28 @@
+# Copyright (c) 2020 UATC, LLC
+#
+# 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.
+
+package(
+    default_visibility = ["//visibility:public"],
+)
+
+cc_library(
+    name = "pfr",
+    hdrs = glob([
+        "include/boost/**",
+    ]),
+    includes = [
+        "include"
+    ],
+    visibility = ["//visibility:public"],
+)

source/neuropod/backends/tensorflow/tf_tensor.hh

@@ -20,6 +20,7 @@ limitations under the License.
 #include "neuropod/internal/error_utils.hh"
 #include "neuropod/internal/logging.hh"
 #include "neuropod/internal/neuropod_tensor.hh"
+#include "tensorflow/core/common_runtime/dma_helper.h"
 #include "tensorflow/core/framework/tensor.h"
 #include "tensorflow/core/public/version.h"
 
@@ -104,14 +105,26 @@ protected:
     void *get_untyped_data_ptr()
     {
         // TODO(vip): make sure this tensor is contiguous
-        return const_cast<char *>(tensor_.tensor_data().data());
+        auto buf = tensorflow::DMAHelper::buffer(&tensor_);
+        if (buf != nullptr)
+        {
+            return buf->data();
+        }
+
+        return nullptr;
     }
 
     // Get a pointer to the underlying data
     const void *get_untyped_data_ptr() const
     {
         // TODO(vip): make sure this tensor is contiguous
-        return tensor_.tensor_data().data();
+        auto buf = tensorflow::DMAHelper::buffer(&tensor_);
+        if (buf != nullptr)
+        {
+            return buf->data();
+        }
+
+        return nullptr;
     }
 };
 

source/neuropod/multiprocess/BUILD

@@ -34,7 +34,6 @@ cc_library(
     srcs = [
         "control_messages.cc",
         "ipc_control_channel.cc",
-        "ope_load_config.cc",
     ],
     hdrs = [
         "control_messages.hh",

source/neuropod/multiprocess/ope_load_config.hh

@@ -31,11 +31,4 @@ struct ope_load_config
     std::vector<BackendLoadSpec> default_backend_overrides;
 };
 
-// Serialization specializations for ope_load_config
-template <>
-void ipc_serialize(std::ostream &out, const ope_load_config &data);
-
-template <>
-void ipc_deserialize(std::istream &in, ope_load_config &data);
-
 } // namespace neuropod

source/neuropod/multiprocess/serialization/BUILD

@@ -23,5 +23,6 @@ cc_library(
     deps = [
         "//neuropod/backends:neuropod_backend",
         "@boost_repo//:boost",
+        "@pfr_repo//:pfr",
     ],
 )

source/neuropod/multiprocess/serialization/ipc_serialization.hh

@@ -18,6 +18,8 @@ limitations under the License.
 #include "neuropod/internal/error_utils.hh"
 #include "neuropod/internal/memory_utils.hh"
 
+#include <boost/pfr/precise.hpp>
+
 #include <istream>
 #include <ostream>
 #include <string>
@@ -62,18 +64,42 @@ inline void checked_read(std::istream &stream, Params &&... params)
 template <typename T>
 inline void ipc_serialize(std::ostream &out, const T &item)
 {
-    static_assert(std::is_integral<T>::value, "The ipc_serialize function must be specialized for the requested type");
+    constexpr bool is_integral  = std::is_integral<T>::value;
+    constexpr bool is_aggregate = std::is_aggregate<T>::value;
+
+    static_assert(is_integral || is_aggregate, "The ipc_serialize function must be specialized for the requested type");
 
-    detail::checked_write(out, reinterpret_cast<const char *>(&item), sizeof(item));
+    if constexpr (is_integral)
+    {
+        // Primitive types
+        detail::checked_write(out, reinterpret_cast<const char *>(&item), sizeof(item));
+    }
+    else if (is_aggregate)
+    {
+        // Structs
+        boost::pfr::for_each_field(item, [&](auto &field) { ipc_serialize(out, field); });
+    }
 }
 
 template <typename T>
 inline void ipc_deserialize(std::istream &in, T &item)
 {
-    static_assert(std::is_integral<T>::value,
+    constexpr bool is_integral  = std::is_integral<T>::value;
+    constexpr bool is_aggregate = std::is_aggregate<T>::value;
+
+    static_assert(is_integral || is_aggregate,
                   "The ipc_deserialize function must be specialized for the requested type");
 
-    detail::checked_read(in, reinterpret_cast<char *>(&item), sizeof(item));
+    if constexpr (is_integral)
+    {
+        // Primitive types
+        detail::checked_read(in, reinterpret_cast<char *>(&item), sizeof(item));
+    }
+    else if (is_aggregate)
+    {
+        // Structs
+        boost::pfr::for_each_field(item, [&](auto &field) { ipc_deserialize(in, field); });
+    }
 }
 
 // Specialization for bool