icexelloss commented on code in PR #35902: URL: https://github.com/apache/arrow/pull/35902#discussion_r1229659237
########## cpp/src/arrow/acero/source_node_test.cc: ########## @@ -0,0 +1,109 @@ +// 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 <gtest/gtest.h> + +#include "arrow/acero/exec_plan.h" +#include "arrow/acero/map_node.h" +#include "arrow/acero/options.h" +#include "arrow/acero/test_nodes.h" + +namespace arrow { +namespace acero { + +struct PauseThenStopNodeOptions : public ExecNodeOptions { + explicit PauseThenStopNodeOptions(int num_pass) : num_pass(num_pass) {} + + int num_pass; +}; + +struct PauseThenStopNode : public MapNode { + static constexpr const char* kKindName = "PauseThenStopNode"; + static constexpr const char* kFactoryName = "pause_then_stop"; + + static void Register() { + auto exec_reg = default_exec_factory_registry(); + if (!exec_reg->GetFactory(kFactoryName).ok()) { + ASSERT_OK(exec_reg->AddFactory(kFactoryName, PauseThenStopNode::Make)); + } + } + + PauseThenStopNode(ExecPlan* plan, std::vector<ExecNode*> inputs, + std::shared_ptr<Schema> output_schema, + const PauseThenStopNodeOptions& options) + : MapNode(plan, inputs, output_schema), num_pass(options.num_pass) {} + + static Result<ExecNode*> Make(ExecPlan* plan, std::vector<ExecNode*> inputs, + const ExecNodeOptions& options) { + RETURN_NOT_OK(ValidateExecNodeInputs(plan, inputs, 1, kKindName)); + auto bp_options = static_cast<const PauseThenStopNodeOptions&>(options); + if (bp_options.num_pass < 2) { + return Status::Invalid("num_pass must be at least 2"); + } + return plan->EmplaceNode<PauseThenStopNode>(plan, inputs, inputs[0]->output_schema(), + bp_options); + } + + const char* kind_name() const override { return kKindName; } + Result<ExecBatch> ProcessBatch(ExecBatch batch) override { + if (num_pass == 2) { + inputs()[0]->PauseProducing(this, 1); + } else if (num_pass == 1) { + ARROW_RETURN_NOT_OK(inputs()[0]->StopProducing()); + } + if (num_pass > 0) --num_pass; + return batch; + } + + int num_pass; +}; + +TEST(SourceNode, PauseThenStop) { + PauseThenStopNode::Register(); + + constexpr int num_pass = 2, num_batches = 10, batch_size = 1; + ASSERT_GE(num_pass, 2); + ASSERT_GT(num_batches, num_pass); + auto t_schema = schema({field("time", int32()), field("value", int32())}); + ASSERT_OK_AND_ASSIGN(auto t_batches, + MakeIntegerBatches({[](int row) -> int64_t { return row; }, + [](int row) -> int64_t { return row + 1; }}, + t_schema, num_batches, batch_size)); + + Declaration t_src = { + "source", SourceNodeOptions(t_batches.schema, + MakeDelayedGen(t_batches, "t_src", /*delay_sec=*/0.5, + /*noisy=*/false))}; + Declaration ctrl = { + PauseThenStopNode::kFactoryName, {t_src}, PauseThenStopNodeOptions(num_pass)}; + + ASSERT_OK_AND_ASSIGN(std::unique_ptr<RecordBatchReader> batch_reader, + DeclarationToReader(ctrl, /*use_threads=*/false)); + + int64_t total_length = 0; + for (;;) { + ASSERT_OK_AND_ASSIGN(auto batch, batch_reader->Next()); + if (!batch) { + break; + } + total_length += batch->num_rows(); + } + ASSERT_EQ(static_cast<int64_t>(num_pass * batch_size), total_length); Review Comment: > I don't think it would help us to test whether a (source) node is paused. The current issue is about the pausing behavior, which manifests in backpressure, not about the pausing state, which may well just be a flag (that may even lack behavior, in an extreme case). It is not perfect and relies on the assumption (if PauseProducing() is called on input node, then backpressure is properly applied). If we really want to check the source node is indeed paused, then I think we need to do what Weston suggest above which is perhaps a bit overkill. Checking the backpresure future or Checking PauseProducing() is called is a reasonable mid ground IMO. > I don't think pausing is the object of testing here; backpressure behavior is, and pausing is just a tool to ensure backpressure. Similar to above, yes it is not the object of testing, but is a proxy for back pressure since I am not aware of a way to check backpressure directly (the backpresure_future_ is a private variable) > I can relate to this, though. If we're aiming for heavy testing of backpressure/cancellation interactions, we should probably create an issue for each kind of testing we have in mind. In my mind, the current PR deals with the current issue and has enough value on its own. The test I have in mind is described above: ``` (1) have a PauseNode/GateNode that calls PauseProducing as soon as it receives input (2) expose a debug method that check if a SourceNode is paused. (SourceNode::IsPaused()) (3) use DeclarationToReader to start the plan (4) Wait for SourceNode to be paused (using SourceNode::IsPaused()) (5) Call StopProducing on the created ExecPlan ``` I agree this PR seems to fix the bug however I'd prefer to have a test that can reflect the actual usage, i.e. ExecPlan::StopProducing() gets called by user when back pressure is applied -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. 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