> (you don't have to strictly follow this form)

**Use case**

Sometimes, for really sophisticated scenarios it can be hard to control the amount of in-progress backups run externally. For the purpose of simpler control we can introduce server-level setting which disallows running concurrent backups of any type. 

Something like this in `config.xml` (enabled by default):
`<allow_concurrent_backups>true</allow_concurrent_backups>`

**Describe the solution you'd like**

It's important that backups can be executed in distributed way on multiple servers. Need to take it into account.

**Describe alternatives you've considered**
External check of `system.backups` table, but it can be complex.

{
        
        
        if (asynchronous_remote_fs_reader)
        {
            try
            {
                LOG_DEBUG(log, "Desctructing remote fs threadpool reader");
                asynchronous_remote_fs_reader->wait();
                asynchronous_remote_fs_reader.reset();
            }
            catch (...)
            {
                tryLogCurrentException(__PRETTY_FUNCTION__);
            }
        }
        if (asynchronous_local_fs_reader)
        {
            try
            {