Function TestTasksSpawnTasks

cpp/src/arrow/util/task_group_test.cc:189–212

Check TaskGroup behaviour with tasks spawning other tasks

// Check TaskGroup behaviour with tasks spawning other tasks
void TestTasksSpawnTasks(std::shared_ptr<TaskGroup> task_group) {
  const int N = 6;

  std::atomic<int> count(0);
  // Make a task that recursively spawns itself
  std::function<std::function<Status()>(int)> make_task = [&](int i) {
    return [&, i]() {
      count++;
      if (i > 0) {
        // Exercise parallelism by spawning two tasks at once and then sleeping
        task_group->Append(make_task(i - 1));
        task_group->Append(make_task(i - 1));
        SleepFor(1e-3);
      }
      return Status::OK();
    };
  };

  task_group->Append(make_task(N));

  ASSERT_OK(task_group->Finish());
  ASSERT_TRUE(task_group->ok());
  ASSERT_EQ(count.load(), (1 << (N + 1)) - 1);
}

// A task that keeps recursing until a barrier is set.
// Using a lambda for this doesn't play well with Thread Sanitizer.