Crystal Fiber Spindles

spindle.cr

class Spindle                                                                                                                                                                                                        [12/193]
  @fiber_count = 0
  @chan = Channel(Nil).new
  @subspindles : Array(Spindle)? = nil
  @on_error : Proc(Exception, Nil)? = nil
            
  def initialize      
  end    
       
  def self.new(existing : Spindle?)
    if e = existing
      return e
    end                
    return Spindle.new
  end  
                        
  def self.group       
    s = Spindle.new             
    with s yield
    s.wait     
  end  
     
  def <<(spindle : Spindle)
    if s = @subspindles                  
      s << spindle
    else
      @subspindles = s = Array(Spindle).new
      s << spindle 
    end
  end             
                          
  def spawn(&block)
    if @chan.closed?
      raise "can't add to closed spindle"
    end        
    @fiber_count += 1
    ::spawn do
      begin 
        block.call
      rescue e
        @on_error.try &.call(e)
      ensure    
        @chan.send nil
      end             
    end
  end
                    
  def wait
    if s = @subspindles
      s.each &.wait
    end
    while @chan.receive?
      @fiber_count -= 1
      break if @fiber_count <= 0
    end
    @chan.close
    nil
  end
  
  def on_error(&@on_error : Exception ->)
  end 
end

s = Spindle.new

s.spawn do
  raise "oh no"
end

s.spawn do
  puts "Dingus!"
end

# We can guarantee that all fibers will complete here
s.wait