Fix bug: pattern consumer's receive() will cause deadlock for topics auto discovery (#7206)

Fixes #7168 

### Motivation

When a pattern consumer is blocked by `receive()`, the `mutex_` will be held until new messages arrived. If the auto discovery timer task found new topics and tried to subscribe them, `mutex_` must be acquired first, then the deadlock happened.

### Modifications

- Release the `mutex_` after the consumer's state was verified.
- Change unit tests to verify that new topics could be subscribed when the consumer's blocked by `receive(Message&)` or `receive(Message&, int)` methods.

### Verifying this change

- [ ] Make sure that the change passes the CI checks.

This change is already covered by existing tests, such as *BasicEndToEndTest.testPatternMultiTopicsConsumerAutoDiscovery*.

Author: BewareMyPower

pulsar-client-cpp/lib/MultiTopicsConsumerImpl.cc

@@ -488,8 +488,8 @@ Result MultiTopicsConsumerImpl::receive(Message& msg) {
         LOG_ERROR("Can not receive when a listener has been set");
         return ResultInvalidConfiguration;
     }
-    messages_.pop(msg);
     lock.unlock();
+    messages_.pop(msg);
 
     unAckedMessageTrackerPtr_->add(msg.getMessageId());
     return ResultOk;
@@ -508,8 +508,8 @@ Result MultiTopicsConsumerImpl::receive(Message& msg, int timeout) {
         return ResultInvalidConfiguration;
     }
 
+    lock.unlock();
     if (messages_.pop(msg, std::chrono::milliseconds(timeout))) {
-        lock.unlock();
         unAckedMessageTrackerPtr_->add(msg.getMessageId());
         return ResultOk;
     } else {

pulsar-client-cpp/tests/BasicEndToEndTest.cc

@@ -2245,102 +2245,88 @@ TEST(BasicEndToEndTest, testPatternMultiTopicsConsumerAutoDiscovery) {
     ASSERT_EQ(consumer.getSubscriptionName(), subName);
     LOG_INFO("created pattern consumer with not match topics at beginning");
 
+    auto createProducer = [&client](Producer &producer, const std::string &topic, int numPartitions) {
+        if (numPartitions > 0) {
+            const std::string url = adminUrl + "admin/v2/persistent/public/default/" + topic + "/partitions";
+            int res = makePutRequest(url, std::to_string(numPartitions));
+            ASSERT_TRUE(res == 204 || res == 409);
+        }
+
+        const std::string fullTopicName = "persistent://public/default/" + topic;
+        Result result = client.createProducer(fullTopicName, producer);
+        ASSERT_EQ(ResultOk, result);
+    };
+
     // 2. create 4 topics, in which 3 match the pattern.
-    std::string topicName1 = "persistent://public/default/patternTopicsAutoConsumerPubSub1";
-    std::string topicName2 = "persistent://public/default/patternTopicsAutoConsumerPubSub2";
-    std::string topicName3 = "persistent://public/default/patternTopicsAutoConsumerPubSub3";
+    std::vector<Producer> producers(4);
+    createProducer(producers[0], "patternTopicsAutoConsumerPubSub1", 2);
+    createProducer(producers[1], "patternTopicsAutoConsumerPubSub2", 3);
+    createProducer(producers[2], "patternTopicsAutoConsumerPubSub3", 4);
     // This will not match pattern
-    std::string topicName4 = "persistent://public/default/notMatchPatternTopicsAutoConsumerPubSub4";
+    createProducer(producers[3], "notMatchPatternTopicsAutoConsumerPubSub4", 4);
 
-    // call admin api to make topics partitioned
-    std::string url1 =
-        adminUrl + "admin/v2/persistent/public/default/patternTopicsAutoConsumerPubSub1/partitions";
-    std::string url2 =
-        adminUrl + "admin/v2/persistent/public/default/patternTopicsAutoConsumerPubSub2/partitions";
-    std::string url3 =
-        adminUrl + "admin/v2/persistent/public/default/patternTopicsAutoConsumerPubSub3/partitions";
-    std::string url4 =
-        adminUrl + "admin/v2/persistent/public/default/notMatchPatternTopicsAutoConsumerPubSub4/partitions";
+    constexpr int messageNumber = 100;
 
-    int res = makePutRequest(url1, "2");
-    ASSERT_FALSE(res != 204 && res != 409);
-    res = makePutRequest(url2, "3");
-    ASSERT_FALSE(res != 204 && res != 409);
-    res = makePutRequest(url3, "4");
-    ASSERT_FALSE(res != 204 && res != 409);
-    res = makePutRequest(url4, "4");
-    ASSERT_FALSE(res != 204 && res != 409);
+    std::thread consumeThread([&consumer] {
+        LOG_INFO("Consuming and acking 300 messages by pattern topics consumer");
+        for (int i = 0; i < 3 * messageNumber; i++) {
+            Message m;
+            // Ensure new topics can be discovered when the consumer is blocked by receive(Message&, int)
+            ASSERT_EQ(ResultOk, consumer.receive(m, 30000));
+            ASSERT_EQ(ResultOk, consumer.acknowledge(m));
+        }
+        // 5. pattern consumer already subscribed 3 topics
+        LOG_INFO("Consumed and acked 300 messages by pattern topics consumer");
 
-    Producer producer1;
-    result = client.createProducer(topicName1, producer1);
-    ASSERT_EQ(ResultOk, result);
-    Producer producer2;
-    result = client.createProducer(topicName2, producer2);
-    ASSERT_EQ(ResultOk, result);
-    Producer producer3;
-    result = client.createProducer(topicName3, producer3);
-    ASSERT_EQ(ResultOk, result);
-    Producer producer4;
-    result = client.createProducer(topicName4, producer4);
-    ASSERT_EQ(ResultOk, result);
-    LOG_INFO("created 3 producers that match, with partitions: 2, 3, 4, and 1 producer not match");
+        // verify no more to receive, because producers[3] not match pattern
+        Message m;
+        ASSERT_EQ(ResultTimeout, consumer.receive(m, 1000));
+    });
 
     // 3. wait enough time to trigger auto discovery
-    std::this_thread::sleep_for(std::chrono::microseconds(2 * 1000 * 1000));
+    std::this_thread::sleep_for(std::chrono::seconds(2));
 
     // 4. produce data.
-    int messageNumber = 100;
-    std::string msgContent = "msg-content";
-    LOG_INFO("Publishing 100 messages by producer 1 synchronously");
-    for (int msgNum = 0; msgNum < messageNumber; msgNum++) {
-        std::stringstream stream;
-        stream << msgContent << msgNum;
-        Message msg = MessageBuilder().setContent(stream.str()).build();
-        ASSERT_EQ(ResultOk, producer1.send(msg));
-    }
-
-    msgContent = "msg-content2";
-    LOG_INFO("Publishing 100 messages by producer 2 synchronously");
-    for (int msgNum = 0; msgNum < messageNumber; msgNum++) {
-        std::stringstream stream;
-        stream << msgContent << msgNum;
-        Message msg = MessageBuilder().setContent(stream.str()).build();
-        ASSERT_EQ(ResultOk, producer2.send(msg));
+    for (size_t i = 0; i < producers.size(); i++) {
+        const std::string msgContent = "msg-content" + std::to_string(i);
+        LOG_INFO("Publishing " << messageNumber << " messages by producer " << i << " synchronously");
+        for (int j = 0; j < messageNumber; j++) {
+            Message msg = MessageBuilder().setContent(msgContent).build();
+            ASSERT_EQ(ResultOk, producers[i].send(msg));
+        }
     }
 
-    msgContent = "msg-content3";
-    LOG_INFO("Publishing 100 messages by producer 3 synchronously");
-    for (int msgNum = 0; msgNum < messageNumber; msgNum++) {
-        std::stringstream stream;
-        stream << msgContent << msgNum;
-        Message msg = MessageBuilder().setContent(stream.str()).build();
-        ASSERT_EQ(ResultOk, producer3.send(msg));
-    }
+    consumeThread.join();
 
-    msgContent = "msg-content4";
-    LOG_INFO("Publishing 100 messages by producer 4 synchronously");
-    for (int msgNum = 0; msgNum < messageNumber; msgNum++) {
-        std::stringstream stream;
-        stream << msgContent << msgNum;
-        Message msg = MessageBuilder().setContent(stream.str()).build();
-        ASSERT_EQ(ResultOk, producer4.send(msg));
-    }
+    consumeThread = std::thread([&consumer] {
+        LOG_INFO("Consuming and acking 100 messages by pattern topics consumer");
+        for (int i = 0; i < messageNumber; i++) {
+            Message m;
+            // Ensure new topics can be discovered when the consumer is blocked by receive(Message&)
+            ASSERT_EQ(ResultOk, consumer.receive(m));
+            ASSERT_EQ(ResultOk, consumer.acknowledge(m));
+        }
+        // 9. pattern consumer subscribed a new topic
+        LOG_INFO("Consumed and acked 100 messages by pattern topics consumer");
 
-    // 5. pattern consumer already subscribed 3 topics
-    LOG_INFO("Consuming and acking 300 messages by pattern topics consumer");
-    for (int i = 0; i < 3 * messageNumber; i++) {
+        // verify no more to receive
         Message m;
-        ASSERT_EQ(ResultOk, consumer.receive(m, 1000));
-        ASSERT_EQ(ResultOk, consumer.acknowledge(m));
-    }
-    LOG_INFO("Consumed and acked 300 messages by pattern topics consumer");
+        ASSERT_EQ(ResultTimeout, consumer.receive(m, 1000));
+    });
+    // 6. Create a producer to a new topic
+    createProducer(producers[0], "patternTopicsAutoConsumerPubSub5", 4);
 
-    // verify no more to receive, because producer4 not match pattern
-    Message m;
-    ASSERT_EQ(ResultTimeout, consumer.receive(m, 1000));
+    // 7. wait enough time to trigger auto discovery
+    std::this_thread::sleep_for(std::chrono::seconds(2));
 
-    ASSERT_EQ(ResultOk, consumer.unsubscribe());
+    // 8. produce data
+    for (int i = 0; i < messageNumber; i++) {
+        Message msg = MessageBuilder().setContent("msg-content-5").build();
+        ASSERT_EQ(ResultOk, producers[0].send(msg));
+    }
 
+    consumeThread.join();
+    ASSERT_EQ(ResultOk, consumer.unsubscribe());
     client.shutdown();
 }