Promises race (#26915)

* Poll type for promises library

* Promises race construct

* Changes to sync required for promise activities

* Automated change: Fix sanity tests

* fix

Co-authored-by: ctiller <ctiller@users.noreply.github.com>

BUILD

@@ -949,6 +949,16 @@ grpc_cc_library(
     deps = ["gpr_platform"],
 )
 
+grpc_cc_library(
+    name = "race",
+    language = "c++",
+    public_hdrs = ["src/core/lib/promise/race.h"],
+    deps = [
+        "gpr_platform",
+        "poll",
+    ],
+)
+
 grpc_cc_library(
     name = "switch",
     language = "c++",

CMakeLists.txt

@@ -923,6 +923,7 @@ if(gRPC_BUILD_TESTS)
   add_dependencies(buildtests_cxx proto_utils_test)
   add_dependencies(buildtests_cxx qps_json_driver)
   add_dependencies(buildtests_cxx qps_worker)
+  add_dependencies(buildtests_cxx race_test)
   add_dependencies(buildtests_cxx raw_end2end_test)
   add_dependencies(buildtests_cxx rbac_translator_test)
   add_dependencies(buildtests_cxx ref_counted_ptr_test)
@@ -13413,6 +13414,41 @@ target_link_libraries(qps_worker
 )
 
 
+endif()
+if(gRPC_BUILD_TESTS)
+
+add_executable(race_test
+  test/core/promise/race_test.cc
+  third_party/googletest/googletest/src/gtest-all.cc
+  third_party/googletest/googlemock/src/gmock-all.cc
+)
+
+target_include_directories(race_test
+  PRIVATE
+    ${CMAKE_CURRENT_SOURCE_DIR}
+    ${CMAKE_CURRENT_SOURCE_DIR}/include
+    ${_gRPC_ADDRESS_SORTING_INCLUDE_DIR}
+    ${_gRPC_RE2_INCLUDE_DIR}
+    ${_gRPC_SSL_INCLUDE_DIR}
+    ${_gRPC_UPB_GENERATED_DIR}
+    ${_gRPC_UPB_GRPC_GENERATED_DIR}
+    ${_gRPC_UPB_INCLUDE_DIR}
+    ${_gRPC_XXHASH_INCLUDE_DIR}
+    ${_gRPC_ZLIB_INCLUDE_DIR}
+    third_party/googletest/googletest/include
+    third_party/googletest/googletest
+    third_party/googletest/googlemock/include
+    third_party/googletest/googlemock
+    ${_gRPC_PROTO_GENS_DIR}
+)
+
+target_link_libraries(race_test
+  ${_gRPC_PROTOBUF_LIBRARIES}
+  ${_gRPC_ALLTARGETS_LIBRARIES}
+  absl::variant
+)
+
+
 endif()
 if(gRPC_BUILD_TESTS)
 

build_autogenerated.yaml

@@ -6244,6 +6244,18 @@ targets:
   deps:
   - grpc++_test_config
   - grpc++_test_util
+- name: race_test
+  gtest: true
+  build: test
+  language: c++
+  headers:
+  - src/core/lib/promise/poll.h
+  - src/core/lib/promise/race.h
+  src:
+  - test/core/promise/race_test.cc
+  deps:
+  - absl/types:variant
+  uses_polling: false
 - name: raw_end2end_test
   gtest: true
   build: test

src/core/lib/promise/race.h

@@ -0,0 +1,80 @@
+// Copyright 2021 gRPC 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 GRPC_CORE_LIB_PROMISE_RACE_H
+#define GRPC_CORE_LIB_PROMISE_RACE_H
+
+#include <grpc/impl/codegen/port_platform.h>
+
+#include <tuple>
+#include "src/core/lib/promise/poll.h"
+
+namespace grpc_core {
+
+namespace promise_detail {
+
+// Implementation type for Race combinator.
+template <typename... Promises>
+class Race;
+
+template <typename Promise, typename... Promises>
+class Race<Promise, Promises...> {
+ public:
+  using Result = decltype(std::declval<Promise>()());
+
+  explicit Race(Promise promise, Promises... promises)
+      : promise_(std::move(promise)), next_(std::move(promises)...) {}
+
+  Result operator()() {
+    // Check our own promise.
+    auto r = promise_();
+    if (absl::holds_alternative<Pending>(r)) {
+      // Check the rest of them.
+      return next_();
+    }
+    // Return the first ready result.
+    return std::move(absl::get<kPollReadyIdx>(std::move(r)));
+  }
+
+ private:
+  // The Promise checked by this instance.
+  Promise promise_;
+  // We recursively expand to check the rest of the instances.
+  Race<Promises...> next_;
+};
+
+template <typename Promise>
+class Race<Promise> {
+ public:
+  using Result = decltype(std::declval<Promise>()());
+  explicit Race(Promise promise) : promise_(std::move(promise)) {}
+  Result operator()() { return promise_(); }
+
+ private:
+  Promise promise_;
+};
+
+}  // namespace promise_detail
+
+/// Run all the promises, return the first result that's available.
+/// If two results are simultaneously available, bias towards the first result
+/// listed.
+template <typename... Promises>
+promise_detail::Race<Promises...> Race(Promises... promises) {
+  return promise_detail::Race<Promises...>(std::move(promises)...);
+}
+
+}  // namespace grpc_core
+
+#endif  // GRPC_CORE_LIB_PROMISE_RACE_H

test/core/promise/BUILD

@@ -60,6 +60,18 @@ grpc_cc_test(
     ],
 )
 
+grpc_cc_test(
+    name = "race_test",
+    srcs = ["race_test.cc"],
+    external_deps = ["gtest"],
+    language = "c++",
+    uses_polling = False,
+    deps = [
+        "//:race",
+        "//test/core/util:grpc_suppressions",
+    ],
+)
+
 grpc_cc_test(
     name = "promise_factory_test",
     srcs = ["promise_factory_test.cc"],

test/core/promise/race_test.cc

@@ -0,0 +1,32 @@
+// Copyright 2021 gRPC 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.
+
+#include "src/core/lib/promise/race.h"
+#include <gtest/gtest.h>
+
+namespace grpc_core {
+
+Poll<int> instant() { return 1; }
+Poll<int> never() { return Pending(); }
+
+TEST(RaceTest, Race1) { EXPECT_EQ(Race(instant)(), Poll<int>(1)); }
+TEST(RaceTest, Race2A) { EXPECT_EQ(Race(instant, never)(), Poll<int>(1)); }
+TEST(RaceTest, Race2B) { EXPECT_EQ(Race(never, instant)(), Poll<int>(1)); }
+
+}  // namespace grpc_core
+
+int main(int argc, char** argv) {
+  ::testing::InitGoogleTest(&argc, argv);
+  return RUN_ALL_TESTS();
+}

tools/run_tests/generated/tests.json

@@ -5825,6 +5825,30 @@
     ],
     "uses_polling": false
   },
+  {
+    "args": [],
+    "benchmark": false,
+    "ci_platforms": [
+      "linux",
+      "mac",
+      "posix",
+      "windows"
+    ],
+    "cpu_cost": 1.0,
+    "exclude_configs": [],
+    "exclude_iomgrs": [],
+    "flaky": false,
+    "gtest": true,
+    "language": "c++",
+    "name": "race_test",
+    "platforms": [
+      "linux",
+      "mac",
+      "posix",
+      "windows"
+    ],
+    "uses_polling": false
+  },
   {
     "args": [],
     "benchmark": false,