[GitHub] [arrow] pitrou commented on a change in pull request #7179: ARROW-8732: [C++] Add basic cancellation API

[GitBox <gi...@apache.org>]

pitrou commented on a change in pull request #7179:
URL: https://github.com/apache/arrow/pull/7179#discussion_r539522546



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File path: cpp/src/arrow/util/cancel_test.cc
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@@ -0,0 +1,202 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you 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 <functional>
+#include <random>
+#include <string>
+#include <thread>
+#include <utility>
+#include <vector>
+
+#include <gtest/gtest.h>
+
+#include "arrow/testing/gtest_util.h"
+#include "arrow/util/cancel.h"
+#include "arrow/util/future.h"
+#include "arrow/util/logging.h"
+
+namespace arrow {
+
+static constexpr double kLongWait = 5;  // seconds
+
+class CancelTest : public ::testing::Test {};
+
+TEST_F(CancelTest, TokenBasics) {
+  {
+    StopToken token;
+    ASSERT_FALSE(token.IsStopRequested());
+    ASSERT_OK(token.Poll());
+
+    token.RequestStop();
+    ASSERT_TRUE(token.IsStopRequested());
+    ASSERT_RAISES(Cancelled, token.Poll());
+  }
+  {
+    StopToken token;
+    token.RequestStop(Status::IOError("Operation cancelled"));
+    ASSERT_TRUE(token.IsStopRequested());
+    ASSERT_RAISES(IOError, token.Poll());
+  }
+}
+
+TEST_F(CancelTest, RequestStopTwice) {
+  StopToken token;
+  token.RequestStop();
+  // Second RequestStop() call is ignored
+  token.RequestStop(Status::IOError("Operation cancelled"));
+  ASSERT_TRUE(token.IsStopRequested());
+  ASSERT_RAISES(Cancelled, token.Poll());
+}
+
+TEST_F(CancelTest, SetCallback) {
+  std::vector<int> results;
+  StopToken token;
+  {
+    const auto cb = token.SetCallback([&](const Status& st) { results.push_back(1); });
+    ASSERT_EQ(results.size(), 0);
+  }
+  {
+    const auto cb = token.SetCallback([&](const Status& st) { results.push_back(1); });
+    ASSERT_EQ(results.size(), 0);
+    token.RequestStop();
+    ASSERT_EQ(results, std::vector<int>{1});
+    token.RequestStop();
+    ASSERT_EQ(results, std::vector<int>{1});
+  }
+  {
+    const auto cb = token.SetCallback([&](const Status& st) { results.push_back(2); });
+    ASSERT_EQ(results, std::vector<int>({1, 2}));
+    token.RequestStop();
+    ASSERT_EQ(results, std::vector<int>({1, 2}));
+  }
+}
+
+TEST_F(CancelTest, StopCallbackMove) {
+  std::vector<int> results;
+  StopToken token;
+
+  StopCallback cb1(&token, [&](const Status& st) { results.push_back(1); });
+  const auto cb2 = std::move(cb1);
+
+  ASSERT_EQ(results.size(), 0);
+  token.RequestStop();
+  ASSERT_EQ(results, std::vector<int>{1});
+}
+
+TEST_F(CancelTest, ThreadedPollSuccess) {
+  constexpr int kNumThreads = 3;
+  constexpr int kMaxLoops = 30000;
+
+  std::vector<Status> results(kNumThreads);
+  std::vector<std::thread> threads;
+
+  StopToken token;
+  auto barrier = Future<void>::Make();
+
+  const auto worker_func = [&](int thread_num) {
+    ARROW_CHECK(barrier.Wait(kLongWait));
+    for (int i = 0; token.Poll().ok() && i < kMaxLoops; ++i) {
+    }
+    results[thread_num] = token.Poll();
+  };
+  for (int i = 0; i < kNumThreads; ++i) {
+    threads.emplace_back(std::bind(worker_func, i));
+  }
+
+  // Let the threads start
+  SleepFor(1e-3);
+  // Unblock all threads
+  barrier.MarkFinished();
+  for (auto& thread : threads) {
+    thread.join();
+  }
+
+  for (const auto& st : results) {
+    ASSERT_OK(st);
+  }
+}
+
+TEST_F(CancelTest, ThreadedPollCancel) {
+  constexpr int kNumThreads = 3;
+  constexpr int kMaxLoops = 1000000;
+
+  std::vector<Status> results(kNumThreads);
+  std::vector<std::thread> threads;
+
+  StopToken token;
+  auto barrier = Future<void>::Make();
+
+  const auto worker_func = [&](int thread_num) {
+    ARROW_CHECK(barrier.Wait(kLongWait));
+    for (int i = 0; token.Poll().ok() && i < kMaxLoops; ++i) {
+    }
+    results[thread_num] = token.Poll();
+  };
+
+  for (int i = 0; i < kNumThreads; ++i) {
+    threads.emplace_back(std::bind(worker_func, i));
+  }
+  // Let the threads start
+  SleepFor(1e-3);
+  // Unblock all threads
+  barrier.MarkFinished();
+  token.RequestStop(Status::IOError("Operation cancelled"));
+  for (auto& thread : threads) {
+    thread.join();
+  }
+
+  for (const auto& st : results) {
+    ASSERT_RAISES(IOError, st);
+  }
+}
+
+TEST_F(CancelTest, ThreadedSetCallbackCancel) {
+  constexpr int kIterations = 100;
+  constexpr double kMaxWait = 1e-3;
+
+  std::default_random_engine gen(42);
+  std::uniform_real_distribution<double> wait_dist(0.0, kMaxWait);
+
+  for (int i = 0; i < kIterations; ++i) {
+    Status result;
+
+    StopToken token;
+    auto barrier = Future<void>::Make();
+
+    const auto worker_func = [&]() {
+      ARROW_CHECK(barrier.Wait(kLongWait));
+      token.RequestStop(Status::IOError("Operation cancelled"));
+    };
+    std::thread thread(worker_func);
+
+    // Unblock thread
+    barrier.MarkFinished();
+    // Use a variable wait time to maximize potential synchronization issues
+    const auto wait_time = wait_dist(gen);
+    if (wait_time > kMaxWait * 0.5) {
+      SleepFor(wait_time);

Review comment:
       Hmm, no, the purpose is to instantiate the `StopCallback` at any possible time, including while the other thread is running `token.RequestStop(...)`.




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