Ordered messages are a type of message provided by ApsaraMQ for RocketMQ. Ordered messages are published and consumed in strict first-in-first-out (FIFO) order. This topic provides sample code on how to send and receive ordered messages by using the HTTP client SDK for C#.
Background information
Ordered messages are divided into the following types:
Globally ordered message: If messages in a topic are of this type, the messages are published and consumed in first-in-first-out (FIFO) order.
Partitionally ordered messages: If messages in a topic are of this type, the messages are distributed to different partitions by using sharding keys. The messages in each partition are consumed in FIFO order. A sharding key is a key field that is used for ordered messages to identify partitions. A sharding key is different from a message key.
For more information, see Ordered messages.
Prerequisites
Before you start, make sure that the following operations are performed:
Install the SDK for C#. For more information, see Prepare the environment.
Create the resources that you want to specify in the code in the ApsaraMQ for RocketMQ console. The resources include instances, topics, and consumer groups. For more information, see Create resources.
Obtain the AccessKey pair of your Alibaba Cloud account. For more information, see Create an AccessKey pair.
Send ordered messages
The following sample code shows how to send ordered messages by using the HTTP client SDK for C#:
using System;
using System.Collections.Generic;
using System.Threading;
using Aliyun.MQ.Model;
using Aliyun.MQ.Model.Exp;
using Aliyun.MQ.Util;
namespace Aliyun.MQ.Sample
{
public class OrderProducerSample
{
// The HTTP endpoint. You can obtain the endpoint in the HTTP Endpoint section of the Instance Details page in the ApsaraMQ for RocketMQ console.
private const string _endpoint = "${HTTP_ENDPOINT}";
// Make sure that the environment variables ALIBABA_CLOUD_ACCESS_KEY_ID and ALIBABA_CLOUD_ACCESS_KEY_SECRET are configured.
// The AccessKey ID that is used for authentication.
private const string _accessKeyId = Environment.GetEnvironmentVariable("ALIBABA_CLOUD_ACCESS_KEY_ID");
// The AccessKey secret that is used for authentication.
private const string _secretAccessKey = Environment.GetEnvironmentVariable("ALIBABA_CLOUD_ACCESS_KEY_SECRET");
// The topic in which the message is produced. You must create the topic in the ApsaraMQ for RocketMQ console.
private const string _topicName = "${TOPIC}";
// The ID of the instance to which the topic belongs. You must create the instance in the ApsaraMQ for RocketMQ console.
// If the instance has a namespace, specify the ID of the instance. If the instance does not have a namespace, set the instanceID parameter to null or an empty string. You can obtain the namespace of the instance on the Instance Details page in the ApsaraMQ for RocketMQ console.
private const string _instanceId = "${INSTANCE_ID}";
private static MQClient _client = new Aliyun.MQ.MQClient(_accessKeyId, _secretAccessKey, _endpoint);
static MQProducer producer = _client.GetProducer(_instanceId, _topicName);
static void Main(string[] args)
{
try
{
// Cyclically send eight messages.
for (int i = 0; i < 8; i++)
{
// The content and tag of the message.
TopicMessage sendMsg = new TopicMessage("hello mq", "tag");
// The custom attributes of the message.
sendMsg.PutProperty("a", i.ToString());
// The sharding key that is used to distribute ordered messages to a specific partition. Sharding keys can be used to identify partitions. A sharding key is different from a message key.
sendMsg.ShardingKey = (i % 2).ToString();
TopicMessage result = producer.PublishMessage(sendMsg);
Console.WriteLine("publis message success:" + result);
}
}
catch (Exception ex)
{
Console.Write(ex);
}
}
}
}Subscribe to ordered messages
The following sample code provides an example on how to subscribe to ordered messages by using the HTTP client SDK for C#:
using System;
using System.Collections.Generic;
using System.Threading;
using Aliyun.MQ.Model;
using Aliyun.MQ.Model.Exp;
using Aliyun.MQ;
namespace Aliyun.MQ.Sample
{
public class OrderConsumerSample
{
// The HTTP endpoint. You can obtain the endpoint in the HTTP Endpoint section of the Instance Details page in the ApsaraMQ for RocketMQ console.
private const string _endpoint = "${HTTP_ENDPOINT}";
// Make sure that the environment variables ALIBABA_CLOUD_ACCESS_KEY_ID and ALIBABA_CLOUD_ACCESS_KEY_SECRET are configured.
// The AccessKey ID that is used for authentication.
private const string _accessKeyId = Environment.GetEnvironmentVariable("ALIBABA_CLOUD_ACCESS_KEY_ID");
// The AccessKey secret that is used for authentication.
private const string _secretAccessKey = Environment.GetEnvironmentVariable("ALIBABA_CLOUD_ACCESS_KEY_SECRET");
// The topic in which the message is produced. You must create the topic in the ApsaraMQ for RocketMQ console.
private const string _topicName = "${TOPIC}";
// The ID of the consumer group that you created in the ApsaraMQ for RocketMQ console.
private const string _groupId = "${GROUP_ID}";
// The ID of the instance to which the topic belongs. You must create the instance in the ApsaraMQ for RocketMQ console.
// If the instance has a namespace, specify the ID of the instance. If the instance does not have a namespace, set the instanceID parameter to null or an empty string. You can obtain the namespace of the instance on the Instance Details page in the ApsaraMQ for RocketMQ console.
private const string _instanceId = "${INSTANCE_ID}";
private static MQClient _client = new Aliyun.MQ.MQClient(_accessKeyId, _secretAccessKey, _endpoint);
static MQConsumer consumer = _client.GetConsumer(_instanceId, _topicName, _groupId, null);
static void Main(string[] args)
{
// Cyclically consume messages in the current thread. We recommend that you use multiple threads to concurrently consume messages.
while (true)
{
try
{
// Consume messages in long polling mode. The consumer may pull partitionally ordered messages from multiple partitions. The consumer consumes messages from the same partition in the order in which the messages are sent.
// Assume that a consumer pulls partitionally ordered messages from one partition. If the broker does not receive an acknowledgement (ACK) for a message from the consumer, the broker delivers the message in the partition to the consumer again.
// The consumer can consume the next batch of messages from a partition only after all messages that are pulled from the partition in the previous batch are acknowledged as consumed.
// In long polling mode, if no message is available for consumption in the topic, requests are suspended on the broker for the specified period of time. If a message becomes available for consumption during the specified period of time, the broker immediately sends a response to the consumer. In this example, the value is specified as 3 seconds.
List<Message> messages = null;
try
{
messages = consumer.ConsumeMessageOrderly(
3, // The maximum number of messages that can be consumed at a time. In this example, the value is specified as 3. The maximum value that you can specify is 16.
3 // The duration of a long polling period. Unit: seconds. In this example, the value is specified as 3. The maximum value that you can specify is 30.
);
}
catch (Exception exp1)
{
if (exp1 is MessageNotExistException)
{
Console.WriteLine(Thread.CurrentThread.Name + " No new message, " + ((MessageNotExistException)exp1).RequestId);
continue;
}
Console.WriteLine(exp1);
Thread.Sleep(2000);
}
if (messages == null)
{
continue;
}
List<string> handlers = new List<string>();
Console.WriteLine(Thread.CurrentThread.Name + " Receive Messages:");
// The message consumption logic.
foreach (Message message in messages)
{
Console.WriteLine(message);
Console.WriteLine("Property a is:" + message.GetProperty("a"));
handlers.Add(message.ReceiptHandle);
}
// If the broker fails to receive an ACK for a message from the consumer before the period of time specified by the Message.nextConsumeTime parameter elapses, the broker delivers the message for consumption again.
// A unique timestamp is specified for the handle of a message each time the message is consumed.
try
{
consumer.AckMessage(handlers);
Console.WriteLine("Ack message success:");
foreach (string handle in handlers)
{
Console.Write("\t" + handle);
}
Console.WriteLine();
}
catch (Exception exp2)
{
// If the handle of a message times out, the broker cannot receive an ACK for the message from the consumer.
if (exp2 is AckMessageException)
{
AckMessageException ackExp = (AckMessageException)exp2;
Console.WriteLine("Ack message fail, RequestId:" + ackExp.RequestId);
foreach (AckMessageErrorItem errorItem in ackExp.ErrorItems)
{
Console.WriteLine("\tErrorHandle:" + errorItem.ReceiptHandle + ",ErrorCode:" + errorItem.ErrorCode + ",ErrorMsg:" + errorItem.ErrorMessage);
}
}
}
}
catch (Exception ex)
{
Console.WriteLine(ex);
Thread.Sleep(2000);
}
}
}
}
}