Class PubSubService
Synopsis
#include <lib/inc/drogon/PubSubService.h>
template <typename MessageType>
class PubSubService : public trantor::NonCopyable
Description
This class template implements a publish-subscribe pattern with multiple named topics.
- Template Parameters:
MessageType- The message type.
Inheritance
Ancestors: NonCopyable
Methods
| clear | remove all topics. | |
| publish | Publish a message to a topic. The message will be broadcasted to every subscriber. | |
| removeTopic | Remove a topic. | |
| size | return the number of topics. | |
| subscribe | Subscribe to a topic. When a message is published to the topic, the handler is invoked by passing the topic and message as parameters. | |
| unsubscribe | Unsubscribe from a topic. |
Source
Lines 125-271 in lib/inc/drogon/PubSubService.h.
template <typename MessageType>
class PubSubService : public trantor::NonCopyable
{
public:
using MessageHandler =
std::function<void(const std::string &, const MessageType &)>;
#if __cplusplus >= 201703L | defined _WIN32
using SharedMutex = std::shared_mutex;
#else
using SharedMutex = std::shared_timed_mutex;
#endif
/**
* @brief Publish a message to a topic. The message will be broadcasted to
* every subscriber.
*/
void publish(const std::string &topicName, const MessageType &message) const
{
std::shared_ptr<Topic<MessageType>> topicPtr;
{
std::shared_lock<SharedMutex> lock(mutex_);
auto iter = topicMap_.find(topicName);
if (iter != topicMap_.end())
{
topicPtr = iter->second;
}
else
{
return;
}
}
topicPtr->publish(message);
}
/**
* @brief Subscribe to a topic. When a message is published to the topic,
* the handler is invoked by passing the topic and message as parameters.
*/
SubscriberID subscribe(const std::string &topicName,
const MessageHandler &handler)
{
auto topicHandler = [topicName, handler](const MessageType &message) {
handler(topicName, message);
};
return subscribeToTopic(topicName, std::move(topicHandler));
}
/**
* @brief Subscribe to a topic. When a message is published to the topic,
* the handler is invoked by passing the topic and message as parameters.
*/
SubscriberID subscribe(const std::string &topicName,
MessageHandler &&handler)
{
auto topicHandler = [topicName, handler = std::move(handler)](
const MessageType &message) {
handler(topicName, message);
};
return subscribeToTopic(topicName, std::move(topicHandler));
}
/**
* @brief Unsubscribe from a topic.
*
* @param topic
* @param id The subscriber ID returned from the subscribe method.
*/
void unsubscribe(const std::string &topicName, SubscriberID id)
{
{
std::shared_lock<SharedMutex> lock(mutex_);
auto iter = topicMap_.find(topicName);
if (iter == topicMap_.end())
{
return;
}
iter->second->unsubscribe(id);
if (!iter->second->empty())
return;
}
std::unique_lock<SharedMutex> lock(mutex_);
auto iter = topicMap_.find(topicName);
if (iter == topicMap_.end())
{
return;
}
if (iter->second->empty())
topicMap_.erase(iter);
}
/**
* @brief return the number of topics.
*/
size_t size() const
{
std::shared_lock<SharedMutex> lock(mutex_);
return topicMap_.size();
}
/**
* @brief remove all topics.
*/
void clear()
{
std::unique_lock<SharedMutex> lock(mutex_);
topicMap_.clear();
}
/**
* @brief Remove a topic
*
*/
void removeTopic(const std::string &topicName)
{
std::unique_lock<SharedMutex> lock(mutex_);
topicMap_.erase(topicName);
}
private:
std::unordered_map<std::string, std::shared_ptr<Topic<MessageType>>>
topicMap_;
mutable SharedMutex mutex_;
SubscriberID subID_ = 0;
SubscriberID subscribeToTopic(
const std::string &topicName,
typename Topic<MessageType>::MessageHandler &&handler)
{
{
std::shared_lock<SharedMutex> lock(mutex_);
auto iter = topicMap_.find(topicName);
if (iter != topicMap_.end())
{
return iter->second->subscribe(std::move(handler));
}
}
std::unique_lock<SharedMutex> lock(mutex_);
auto iter = topicMap_.find(topicName);
if (iter != topicMap_.end())
{
return iter->second->subscribe(std::move(handler));
}
auto topicPtr = std::make_shared<Topic<MessageType>>();
auto id = topicPtr->subscribe(std::move(handler));
topicMap_[topicName] = std::move(topicPtr);
return id;
}
};