class EventMachine::Synchrony::ConnectionPool

- if pool is full, yield the current fiber until connection is available
- if connection is available, pass it back to the calling block
Acquire a lock on a connection and assign it to executing fiber

def acquire(fiber)
  if conn = @available.pop
    @reserved[fiber.object_id] = conn
    conn
  else
    Fiber.yield @pending.push fiber
    acquire(fiber)
  end
end