The high concurrent performance of Meresco is not achieved by deploying an army of processes and threads but by the asynchronous power of Weightless.
Server processes are either synchronous or asynchronous.
Synchronous servers accept a connection and wait for the whole request to be received before processing. Every connection is handled by a single thread or process. The program flow in synchronous servers seems conceptionally easier, but often gets complicated in practice by all kinds of locking issues.
Asynchronous servers read when there is data available and send responses when there is something to send, all in one single-threaded process. Code that runs within a asynchronous server needs to be crafted with special care to allow for fair resource sharing between requests. This is known as cooperative scheduling. Because there are no threads that interrupt and lock each other (simplifying the software when compared to the alternative) the server is able to handle a large number of concurrent connections without a noticable speed penalty.
Weightless was developed to bring the advantages of asynchronous I/O to Meresco. Weightless is a lightweight framework that provides the infrastructure for asynchronous servers. Weightless comes with HTTP and HTTPS server functionality. By making use of Python generators (co-routines) to facilitate input and output, Weightless provides an easy to use mechanism to read and write data.
More information on weightless can be found at: http://weightless.io