ClickHouse/src/Storages/RabbitMQ/RabbitMQHandler.cpp

#include <common/logger_useful.h>
#include <Storages/RabbitMQ/RabbitMQHandler.h>

namespace DB
{

enum
{
    Lock_timeout = 50, 
    Max_threads_to_pass = 10
};


RabbitMQHandler::RabbitMQHandler(event_base * evbase_, Poco::Logger * log_) :
    LibEventHandler(evbase_),
    evbase(evbase_),
    log(log_)
{
}


void RabbitMQHandler::onError(AMQP::TcpConnection * connection, const char * message) 
{
    LOG_ERROR(log, "Library error report: {}", message);

    if (!connection->usable() || !connection->ready())
    {
        LOG_ERROR(log, "Connection lost completely");
    }

    stop();
}


void RabbitMQHandler::start(std::atomic<bool> & check_param)
{
    /* The object of this class is shared between concurrent consumers (who share the same connection == share the same
     * event loop). But the loop should not be attempted to start if it is already running. 
     */
    if (mutex_before_event_loop.try_lock_for(std::chrono::milliseconds(Lock_timeout)))
    {
        /* The callback, which changes this variable, could have already been activated by another thread while we waited
         * for the mutex to unlock (as it runs all active events on the connection). This means that there is no need to
         * start event loop again.
         */
        if (!check_param)
        {
            event_base_loop(evbase, EVLOOP_NONBLOCK); 
        }

        mutex_before_event_loop.unlock();
    }
    else
    {
        if (++count_passed == Max_threads_to_pass)
        {
            /* Event loop is blocking to the thread that started it and it is not good to block one single thread as it loops 
             * untill there are no active events, but there can be too many of them for one thread to be blocked for so long.
             */
            stop();
            count_passed = 0;
        }
    }
}

void RabbitMQHandler::stop()
{
    if (mutex_before_loop_stop.try_lock_for(std::chrono::milliseconds(0)))
    {
        event_base_loopbreak(evbase);
        mutex_before_loop_stop.unlock();
    }
}

}