C++ migration: add AsyncQueue, the C++ version of FSTDispatchQueue (#1176)

AsyncQueue is a queue that executes given operations asynchronously,
enforcing that only a single operation is executing at any given time,
and that in-progress operations don't spawn more operations. The actual
execution is delegated to a platform-specific executor. Executor is an
interface for a FIFO queue that executes given operations serially. Two
implementations of Executor, one using libdispatch and the other using
C++11 standard library, are provided.

AsyncQueue is not used anywhere in the code base at this point.

1 files changed, 110 insertions, 0 deletions

diff --git a/Firestore/core/test/firebase/firestore/util/executor_test.cc b/Firestore/core/test/firebase/firestore/util/executor_test.cc
new file mode 100644
index 0000000..5cf389b
--- /dev/null
+++ b/Firestore/core/test/firebase/firestore/util/executor_test.cc
@@ -0,0 +1,110 @@
+/*
+ * Copyright 2018 Google
+ *
+ * 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 "Firestore/core/test/firebase/firestore/util/executor_test.h"
+
+#include <chrono>  // NOLINT(build/c++11)
+#include <cstdlib>
+#include <future>  // NOLINT(build/c++11)
+#include <string>
+#include <thread>  // NOLINT(build/c++11)
+
+#include "Firestore/core/src/firebase/firestore/util/executor.h"
+#include "gtest/gtest.h"
+
+namespace firebase {
+namespace firestore {
+namespace util {
+
+namespace chr = std::chrono;
+using internal::Executor;
+
+namespace {
+
+DelayedOperation Schedule(Executor* const executor,
+                          const Executor::Milliseconds delay,
+                          Executor::Operation&& operation) {
+  const Executor::Tag no_tag = -1;
+  return executor->Schedule(
+      delay, Executor::TaggedOperation{no_tag, std::move(operation)});
+}
+
+}  // namespace
+
+TEST_P(ExecutorTest, Execute) {
+  executor->Execute([&] { signal_finished(); });
+  EXPECT_TRUE(WaitForTestToFinish());
+}
+
+TEST_P(ExecutorTest, DestructorDoesNotBlockIfThereArePendingTasks) {
+  const auto future = std::async(std::launch::async, [&] {
+    auto another_executor = GetParam()();
+    Schedule(another_executor.get(), chr::minutes(5), [] {});
+    Schedule(another_executor.get(), chr::minutes(10), [] {});
+    // Destructor shouldn't block waiting for the 5/10-minute-away operations.
+  });
+
+  ABORT_ON_TIMEOUT(future);
+}
+
+TEST_P(ExecutorTest, CanScheduleOperationsInTheFuture) {
+  std::string steps;
+
+  executor->Execute([&steps] { steps += '1'; });
+  Schedule(executor.get(), Executor::Milliseconds(5), [&] {
+    steps += '4';
+    signal_finished();
+  });
+  Schedule(executor.get(), Executor::Milliseconds(1),
+           [&steps] { steps += '3'; });
+  executor->Execute([&steps] { steps += '2'; });
+
+  EXPECT_TRUE(WaitForTestToFinish());
+  EXPECT_EQ(steps, "1234");
+}
+
+TEST_P(ExecutorTest, CanCancelDelayedOperations) {
+  std::string steps;
+
+  executor->Execute([&] {
+    executor->Execute([&steps] { steps += '1'; });
+
+    DelayedOperation delayed_operation = Schedule(
+        executor.get(), Executor::Milliseconds(1), [&steps] { steps += '2'; });
+
+    Schedule(executor.get(), Executor::Milliseconds(5), [&] {
+      steps += '3';
+      signal_finished();
+    });
+
+    delayed_operation.Cancel();
+  });
+
+  EXPECT_TRUE(WaitForTestToFinish());
+  EXPECT_EQ(steps, "13");
+}
+
+TEST_P(ExecutorTest, DelayedOperationIsValidAfterTheOperationHasRun) {
+  DelayedOperation delayed_operation = Schedule(
+      executor.get(), Executor::Milliseconds(1), [&] { signal_finished(); });
+
+  EXPECT_TRUE(WaitForTestToFinish());
+  EXPECT_NO_THROW(delayed_operation.Cancel());
+}
+
+}  // namespace util
+}  // namespace firestore
+}  // namespace firebase