bkietz commented on a change in pull request #9095:
URL: https://github.com/apache/arrow/pull/9095#discussion_r556129806
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File path: cpp/src/arrow/util/future_test.cc
##########
@@ -832,6 +832,145 @@ TEST(FutureCompletionTest, FutureVoid) {
}
}
+TEST(FutureAllTest, Simple) {
+ auto f1 = Future<int>::Make();
+ auto f2 = Future<int>::Make();
+ std::vector<Future<int>> futures = {f1, f2};
+ auto combined = arrow::All(futures);
+
+ ARROW_UNUSED(combined.Then([](std::vector<Result<int>> results) {
+ ASSERT_EQ(2, results.size());
+ ASSERT_EQ(1, *results[0]);
+ ASSERT_EQ(2, *results[1]);
+ }));
+
+ // Finish in reverse order, results should still be delivered in proper order
+ AssertNotFinished(combined);
+ f2.MarkFinished(2);
+ AssertNotFinished(combined);
+ f1.MarkFinished(1);
+ AssertSuccessful(combined);
+}
+
+TEST(FutureAllTest, Failure) {
+ auto f1 = Future<int>::Make();
+ auto f2 = Future<int>::Make();
+ auto f3 = Future<int>::Make();
+ std::vector<Future<int>> futures = {f1, f2, f3};
+ auto combined = arrow::All(futures);
+
+ ARROW_UNUSED(combined.Then([](std::vector<Result<int>> results) {
+ ASSERT_EQ(3, results.size());
+ ASSERT_EQ(1, *results[0]);
+ ASSERT_EQ(Status::IOError("XYZ"), results[1].status());
+ ASSERT_EQ(3, *results[2]);
+ }));
+
+ f1.MarkFinished(1);
+ f2.MarkFinished(Status::IOError("XYZ"));
+ f3.MarkFinished(3);
+
+ AssertFinished(combined);
+}
+
+TEST(FutureLoopTest, Sync) {
+ struct {
+ int i = 0;
+ Future<int> Get() { return Future<int>::MakeFinished(i++); }
+ } IntSource;
+
+ bool do_fail = false;
+ std::vector<int> ints;
+ auto loop_body = [&] {
+ return IntSource.Get().Then([&](int i) -> Result<ControlFlow<int>> {
+ if (do_fail && i == 3) {
+ return Status::IOError("xxx");
+ }
+
+ if (i == 5) {
+ int sum = 0;
+ for (int i : ints) sum += i;
+ return Break(sum);
+ }
+
+ ints.push_back(i);
+ return Continue();
+ });
+ };
+
+ {
+ auto sum_fut = Loop(loop_body);
+ AssertSuccessful(sum_fut);
+
+ ASSERT_OK_AND_ASSIGN(auto sum, sum_fut.result());
+ ASSERT_EQ(sum, 0 + 1 + 2 + 3 + 4);
+ }
+
+ {
+ do_fail = true;
+ IntSource.i = 0;
+ auto sum_fut = Loop(loop_body);
+ AssertFailed(sum_fut);
+ ASSERT_RAISES(IOError, sum_fut.result());
+ }
+}
+
+TEST(FutureLoopTest, EmptyBreakValue) {
+ Future<> none_fut =
+ Loop([&] { return Future<>::MakeFinished().Then([&](...) { return
Break(); }); });
+ AssertSuccessful(none_fut);
+}
+
+TEST(FutureLoopTest, MoveOnlyBreakValue) {
+ Future<MoveOnlyDataType> one_fut = Loop([&] {
+ return Future<int>::MakeFinished(1).Then(
+ [&](int i) { return Break(MoveOnlyDataType(i)); });
+ });
+ AssertSuccessful(one_fut);
+ ASSERT_OK_AND_ASSIGN(auto one, std::move(one_fut).result());
+ ASSERT_EQ(one, 1);
+}
+
+TEST(FutureLoopTest, StackOverflow) {
+ // Looping over futures is normally a rather recursive task. If the futures
complete
+ // synchronously (because they are already finished) it could lead to a
stack overflow
+ // if care is not taken.
+ int counter = 0;
+ auto loop_body = [&counter]() -> Future<ControlFlow<int>> {
+ while (counter < 1000000) {
+ counter++;
+ return Future<ControlFlow<int>>::MakeFinished(Continue());
Review comment:
For lambdas without an explicit trailing return type, all return
statements *must* return the same type, so you'd have to choose which
boilerplate is preferable. IMHO, the trailing return type and implicit
conversion look prettiest
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