ApsaraMQ for RocketMQ provides a distributed transaction processing feature similar to eXtended Architecture (X/Open XA) to ensure transaction consistency in ApsaraMQ for RocketMQ. This topic provides the sample code on how to send and receive transactional messages by using the HTTP client SDK for C++.
Background information
The following figure shows the interaction process of transactional messages.
For more information, see Transactional 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 transactional messages
The following sample code provides an example on how to send transactional messages by using the HTTP client SDK for C++:
//#include <iostream>
#include <fstream>
#ifdef _WIN32
#include <windows.h>
#include <process.h>
#else
#include "pthread.h"
#endif
#include "mq_http_sdk/mq_client.h"
using namespace std;
using namespace mq::http::sdk;
const int32_t pubMsgCount = 4;
const int32_t halfCheckCount = 3;
void processCommitRollError(AckMessageResponse& bdmResp, const std::string& messageId) {
if (bdmResp.isSuccess()) {
cout << "Commit/Roll Transaction Suc: " << messageId << endl;
return;
}
const std::vector<AckMessageFailedItem>& failedItems =
bdmResp.getAckMessageFailedItem();
for (std::vector<AckMessageFailedItem>::const_iterator iter = failedItems.begin();
iter != failedItems.end(); ++iter)
{
cout << "Commit/Roll Transaction ERROR: " << iter->errorCode
<< " " << iter->receiptHandle << endl;
}
}
#ifdef WIN32
unsigned __stdcall consumeHalfMessageThread(void *arg)
#else
void* consumeHalfMessageThread(void *arg)
#endif
{
MQTransProducerPtr transProducer = *(MQTransProducerPtr*)(arg);
int count = 0;
do {
std::vector<Message> halfMsgs;
try {
// Consume messages in long polling mode.
// In long polling mode, if no message in the topic is available for consumption, the request is suspended on the broker for the specified period of time. If a message becomes available for consumption within the specified period of time, the broker immediately sends a response to the consumer. In this example, the value is specified as 3 seconds.
transProducer->consumeHalfMessage(
1, // The maximum number of messages that can be consumed at a time. In this example, the value is specified as 1. The maximum value that you can specify is 16.
3, // The duration of a long polling cycle. Unit: seconds. In this example, the value is specified as 3. The maximum value that you can specify is 30.
halfMsgs
);
} catch (MQServerException& me) {
if (me.GetErrorCode() == "MessageNotExist") {
cout << "No half message to consume! RequestId: " + me.GetRequestId() << endl;
continue;
}
cout << "Request Failed: " + me.GetErrorCode() + ".RequestId: " + me.GetRequestId() << endl;
}
if (halfMsgs.size() == 0) {
continue;
}
cout << "Consume Half: " << halfMsgs.size() << " Messages!" << endl;
// Process the half message.
std::vector<std::string> receiptHandles;
for (std::vector<Message>::iterator iter = halfMsgs.begin();
iter != halfMsgs.end(); ++iter)
{
cout << "MessageId: " << iter->getMessageId()
<< " PublishTime: " << iter->getPublishTime()
<< " Tag: " << iter->getMessageTag()
<< " Body: " << iter->getMessageBody()
<< " FirstConsumeTime: " << iter->getFirstConsumeTime()
<< " NextConsumeTime: " << iter->getNextConsumeTime()
<< " ConsumedTimes: " << iter->getConsumedTimes()
<< " Properties: " << iter->getPropertiesAsString()
<< " Key: " << iter->getMessageKey() << endl;
int32_t consumedTimes = iter->getConsumedTimes();
const std::string propA = iter->getProperty("a");
const std::string handle = iter->getReceiptHandle();
AckMessageResponse bdmResp;
if (propA == "1") {
cout << "Commit msg.." << endl;
transProducer->commit(handle, bdmResp);
count++;
} else if(propA == "2") {
if (consumedTimes > 1) {
cout << "Commit msg.." << endl;
transProducer->commit(handle, bdmResp);
count++;
} else {
cout << "Commit Later!!!" << endl;
}
} else if(propA == "3") {
cout << "Rollback msg.." << endl;
transProducer->rollback(handle, bdmResp);
count++;
} else {
transProducer->commit(handle, bdmResp);
cout << "Unkown msg.." << endl;
}
// If the transactional message is committed or rolled back after the time specified by the NextConsumeTime parameter elapses, the commit or rollback fails.
processCommitRollError(bdmResp, iter->getMessageId());
}
} while(count < halfCheckCount);
#ifdef WIN32
return 0;
#else
return NULL;
#endif
}
int main() {
MQClient mqClient(
// The HTTP endpoint. You can obtain the endpoint in the HTTP Endpoint section of the Instance Details page in the ApsaraMQ for RocketMQ console.
"${HTTP_ENDPOINT}",
// Make sure that the environment variables ALIBABA_CLOUD_ACCESS_KEY_ID and ALIBABA_CLOUD_ACCESS_KEY_SECRET are configured.
// The AccessKey ID that is used for authentication.
System.getenv("ALIBABA_CLOUD_ACCESS_KEY_ID"),
// The AccessKey secret that is used for authentication.
System.getenv("ALIBABA_CLOUD_ACCESS_KEY_SECRET")
);
// The topic in which the message is produced. You must create the topic in the ApsaraMQ for RocketMQ console.
string topic = "${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.
string instanceId = "${INSTANCE_ID}";
// The ID of the consumer group that you created in the ApsaraMQ for RocketMQ console.
string groupId = "${GROUP_ID}";
MQTransProducerPtr transProducer;
if (instanceId == "") {
transProducer = mqClient.getTransProducerRef(topic, groupId);
} else {
transProducer = mqClient.getTransProducerRef(instanceId, topic, groupId);
}
// The client needs a thread or a process to process unacknowledged transactional messages.
// Start a thread to process unacknowledged transactional messages.
#ifdef WIN32
HANDLE thread;
unsigned int threadId;
thread = (HANDLE)_beginthreadex(NULL, 0, consumeHalfMessageThread, &transProducer, 0, &threadId);
#else
pthread_t thread;
pthread_create(&thread, NULL, consumeHalfMessageThread, static_cast<void *>(&transProducer));
#endif
try {
for (int i = 0; i < pubMsgCount; i++)
{
PublishMessageResponse pmResp;
TopicMessage pubMsg("Hello, mq, trans_msg!");
pubMsg.putProperty("a",std::to_string(i));
pubMsg.setMessageKey("ImKey");
pubMsg.setTransCheckImmunityTime(10);
transProducer->publishMessage(pubMsg, pmResp);
cout << "Publish mq message success. Topic:" << topic
<< ", msgId:" << pmResp.getMessageId()
<< ", bodyMD5:" << pmResp.getMessageBodyMD5()
<< ", Handle:" << pmResp.getReceiptHandle() << endl;
if (i == 0) {
// After the producer sends the transactional message, the broker obtains the handle of the half message that corresponds to the transactional message and commits or rolls back the transactional message based on the status of the handle.
// If the transactional message is committed or rolled back after the time specified by the TransCheckImmunityTime parameter elapses, the commit or rollback fails.
AckMessageResponse bdmResp;
transProducer->commit(pmResp.getReceiptHandle(), bdmResp);
processCommitRollError(bdmResp, pmResp.getMessageId());
}
}
} catch (MQServerException& me) {
cout << "Request Failed: " + me.GetErrorCode() << ", requestId is:" << me.GetRequestId() << endl;
} catch (MQExceptionBase& mb) {
cout << "Request Failed: " + mb.ToString() << endl;
}
#ifdef WIN32
WaitForSingleObject(thread, INFINITE);
CloseHandle(thread);
#else
pthread_join(thread, NULL);
#endif
return 0;
}Subscribe to transactional messages
The following sample code provides an example on how to subscribe to transactional messages by using the HTTP client SDK for C++:
#include <vector>
#include <fstream>
#include "mq_http_sdk/mq_client.h"
#ifdef _WIN32
#include <windows.h>
#else
#include <unistd.h>
#endif
using namespace std;
using namespace mq::http::sdk;
int main() {
MQClient mqClient(
// The HTTP endpoint. You can obtain the endpoint in the HTTP Endpoint section of the Instance Details page in the ApsaraMQ for RocketMQ console.
"${HTTP_ENDPOINT}",
// Make sure that the environment variables ALIBABA_CLOUD_ACCESS_KEY_ID and ALIBABA_CLOUD_ACCESS_KEY_SECRET are configured.
// The AccessKey ID that is used for authentication.
System.getenv("ALIBABA_CLOUD_ACCESS_KEY_ID"),
// The AccessKey secret that is used for authentication.
System.getenv("ALIBABA_CLOUD_ACCESS_KEY_SECRET")
);
// The topic in which the message is produced. You must create the topic in the ApsaraMQ for RocketMQ console.
string topic = "${TOPIC}";
// The ID of the consumer group that you created in the ApsaraMQ for RocketMQ console.
string groupId = "${GROUP_ID}";
// The ID of the instance to which the topic belongs. You must create the instance in the ApsaraMQ for RocketMQ console.
// If the instance has a namespace, specify the ID of the instance. If the instance does not have a namespace, set the instanceID parameter to null or an empty string. You can obtain the namespace of the instance on the Instance Details page in the ApsaraMQ for RocketMQ console.
string instanceId = "${INSTANCE_ID}";
MQConsumerPtr consumer;
if (instanceId == "") {
consumer = mqClient.getConsumerRef(topic, groupId);
} else {
consumer = mqClient.getConsumerRef(instanceId, topic, groupId, "");
}
do {
try {
std::vector<Message> messages;
// Consume messages in long polling mode.
// In long polling mode, if no message in the topic is available for consumption, the request is suspended on the broker for the specified period of time. If a message becomes available for consumption within the specified period of time, the broker immediately sends a response to the consumer. In this example, the value is specified as 3 seconds.
consumer->consumeMessage(
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 cycle. Unit: seconds. In this example, the value is specified as 3. The maximum value that you can specify is 30.
messages
);
cout << "Consume: " << messages.size() << " Messages!" << endl;
// The message consumption logic.
std::vector<std::string> receiptHandles;
for (std::vector<Message>::iterator iter = messages.begin();
iter != messages.end(); ++iter)
{
cout << "MessageId: " << iter->getMessageId()
<< " PublishTime: " << iter->getPublishTime()
<< " Tag: " << iter->getMessageTag()
<< " Body: " << iter->getMessageBody()
<< " FirstConsumeTime: " << iter->getFirstConsumeTime()
<< " NextConsumeTime: " << iter->getNextConsumeTime()
<< " ConsumedTimes: " << iter->getConsumedTimes()
<< " Properties: " << iter->getPropertiesAsString()
<< " Key: " << iter->getMessageKey() << endl;
receiptHandles.push_back(iter->getReceiptHandle());
}
// Obtain an acknowledgement (ACK) from the consumer.
// If the broker fails to receive an ACK for a message from the consumer before the period of time that is 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.
AckMessageResponse bdmResp;
consumer->ackMessage(receiptHandles, bdmResp);
if (!bdmResp.isSuccess()) {
// If the handle of a message times out, the broker cannot receive an ACK for the message from the consumer.
const std::vector<AckMessageFailedItem>& failedItems =
bdmResp.getAckMessageFailedItem();
for (std::vector<AckMessageFailedItem>::const_iterator iter = failedItems.begin();
iter != failedItems.end(); ++iter)
{
cout << "AckFailedItem: " << iter->errorCode
<< " " << iter->receiptHandle << endl;
}
} else {
cout << "Ack: " << messages.size() << " messages suc!" << endl;
}
} catch (MQServerException& me) {
if (me.GetErrorCode() == "MessageNotExist") {
cout << "No message to consume! RequestId: " + me.GetRequestId() << endl;
continue;
}
cout << "Request Failed: " + me.GetErrorCode() + ".RequestId: " + me.GetRequestId() << endl;
#ifdef _WIN32
Sleep(2000);
#else
usleep(2000 * 1000);
#endif
} catch (MQExceptionBase& mb) {
cout << "Request Failed: " + mb.ToString() << endl;
#ifdef _WIN32
Sleep(2000);
#else
usleep(2000 * 1000);
#endif
}
} while(true);
}