Class: EventMachine::Pool

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

Overview

A simple async resource pool based on a resource and work queue. Resources are enqueued and work waits for resources to become available.

Resources are expected to be controlled by an object responding to a deferrable/completion style API with callback and errback blocks.

Examples:

require 'em-http-request'

EM.run do
  pool  = EM::Pool.new
  spawn = lambda { pool.add EM::HttpRequest.new('http://example.org') }
  10.times { spawn[] }
  done, scheduled = 0, 0

  check = lambda do
    done += 1
    if done >= scheduled
      EM.stop
    end
  end

  pool.on_error { |conn| spawn[] }

  100.times do |i|
    scheduled += 1
    pool.perform do |conn|
      req = conn.get :path => '/', :keepalive => true

      req.callback do
        p [:success, conn.object_id, i, req.response.size]
        check[]
      end

      req.errback { check[] }

      req
    end
  end
end

Instance Method Summary collapse

Constructor Details

#initializePool

Returns a new instance of Pool



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# File 'lib/em/pool.rb', line 45

def initialize
  @resources = EM::Queue.new
  @removed = []
  @contents = []
  @on_error = nil
end

Instance Method Details

#add(resource) ⇒ Object



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# File 'lib/em/pool.rb', line 52

def add resource
  @contents << resource
  requeue resource
end

#contentsObject

Returns a list for introspection purposes only. You should NEVER call modification or work oriented methods on objects in this list. A good example use case is periodic statistics collection against a set of connection resources.

Examples:

pool.contents.inject(0) { |sum, connection| connection.num_bytes }


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# File 'lib/em/pool.rb', line 69

def contents
  @contents.dup
end

#num_waitingObject

A peek at the number of enqueued jobs waiting for resources



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# File 'lib/em/pool.rb', line 107

def num_waiting
  @resources.num_waiting
end

#on_error(*a, &b) ⇒ Object

Define a default catch-all for when the deferrables returned by work blocks enter a failed state. By default all that happens is that the resource is returned to the pool. If on_error is defined, this block is responsible for re-adding the resource to the pool if it is still usable. In other words, it is generally assumed that on_error blocks explicitly handle the rest of the lifetime of the resource.



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# File 'lib/em/pool.rb', line 79

def on_error *a, &b
  @on_error = EM::Callback(*a, &b)
end

#perform(*a, &b) ⇒ Object Also known as: reschedule

Perform a given #call-able object or block. The callable object will be called with a resource from the pool as soon as one is available, and is expected to return a deferrable.

The deferrable will have callback and errback added such that when the deferrable enters a finished state, the object is returned to the pool.

If on_error is defined, then objects are not automatically returned to the pool.



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# File 'lib/em/pool.rb', line 92

def perform(*a, &b)
  work = EM::Callback(*a, &b)

  @resources.pop do |resource|
    if removed? resource
      @removed.delete resource
      reschedule work
    else
      process work, resource
    end
  end
end

#remove(resource) ⇒ Object



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# File 'lib/em/pool.rb', line 57

def remove resource
  @contents.delete resource
  @removed << resource
end

#removed?(resource) ⇒ Boolean

Removed will show resources in a partial pruned state. Resources in the removed list may not appear in the contents list if they are currently in use.

Returns:

  • (Boolean)


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# File 'lib/em/pool.rb', line 114

def removed? resource
  @removed.include? resource
end