Scheduler Threads

You can explicitly spawn a pool of non-blocking scheduler threads and divide work across traditional blocking and non-blocking threads, using location blocks.

This allows you to safely dip your toes into using non-blocking threads for specific I/O heavy operations without having to port an entire application to non-blocking I/O.

To use blocking and non-blocking threads in conjunction you need to perform several steps.

1. Configure a thread pool using threads
2. Configure a separate non-blocking thread pool using scheduler_threads (By opting into this option you automatically make the ordinary thread pool blocking)
3. Enable a fiber_scheduler
4. Mount your app as non-blocking for selected routes. (Using either run, rackup_file or endpoint)

Configuration

Here is an example configuration of the all of the above E.g.

threads 3 # 3 threads (opting into scheduler threads make these blocking)
scheduler_threads 1 # 1 non-blocking scheduler thread
fiber_scheduler true

# We mount the same app *twice*.
# For a specific route prefix, all requests will be sent to non blocking threads.
# All others fall through to the default mount
location "/heavy_io/*" do
  rackup_file "./config.ru", nonblocking: true
end

rackup_file "./config.ru"