Class: EventMachine::ThreadedResource

Inherits:
Object
  • Object
show all
Defined in:
lib/em/threaded_resource.rb

Overview

= EventMachine::ThreadedResource

A threaded resource is a "quick and dirty" wrapper around the concept of wiring up synchronous code into a standard EM::Pool. This is useful to keep interfaces coherent and provide a simple approach at "making an interface async-ish".

General usage is to wrap libraries that do not support EventMachine, or to have a specific number of dedicated high-cpu worker resources.

== Basic Usage example

This example requires the cassandra gem. The cassandra gem contains an EventMachine interface, but it's sadly Fiber based and thus only works on 1.9. It also requires (potentially) complex stack switching logic to reach completion of nested operations. By contrast this approach provides a block in which normal synchronous code can occur, but makes no attempt to wire the IO into EventMachines C++ IO implementations, instead relying on the reactor pattern in rb_thread_select.

cassandra_dispatcher = ThreadedResource.new do

 Cassandra.new('allthethings', '127.0.0.1:9160')

end

pool = EM::Pool.new

pool.add cassandra_dispatcher

# If we don't care about the result: pool.perform do |dispatcher|

 # The following block executes inside a dedicated thread, and should not
 # access EventMachine things:
 dispatcher.dispatch do |cassandra|
   cassandra.insert(:Things, '10', 'stuff' => 'things')
 end

end

# Example where we care about the result: pool.perform do |dispatcher|

 # The dispatch block is executed in the resources thread.
 completion = dispatcher.dispatch do |cassandra|
   cassandra.get(:Things, '10', 'stuff')
 end

 # This block will be yielded on the EM thread:
 completion.callback do |result|
   EM.do_something_with(result)
 end

 completion

end

Instance Method Summary (collapse)

Constructor Details

- (ThreadedResource) initialize

The block should return the resource that will be yielded in a dispatch.



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# File 'lib/em/threaded_resource.rb', line 56

def initialize
  @resource = yield

  @running = true
  @queue   = ::Queue.new
  @thread  = Thread.new do
    @queue.pop.call while @running
  end
end

Instance Method Details

- (Object) dispatch

Called on the EM thread, generally in a perform block to return a completion for the work.



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# File 'lib/em/threaded_resource.rb', line 68

def dispatch
  completion = EM::Completion.new
  @queue << lambda do
    begin
      result = yield @resource
      completion.succeed result
    rescue Exception => e
      completion.fail e
    end
  end
  completion
end

- (Object) shutdown

Kill the internal thread. should only be used to cleanup - generally only required for tests.



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# File 'lib/em/threaded_resource.rb', line 83

def shutdown
  @running = false
  @queue << lambda {}
  @thread.join
end