Class: Hoodoo::Communicators::Slow

Inherits:
Object
  • Object
show all
Defined in:
lib/hoodoo/communicators/slow.rb

Overview

See Hoodoo::Communicators::Pool for details.

A “slow communicator”. Subclass this to create a class where instances are invoked via Hoodoo::Communicators::Slow#communicate with some parameter and, in response, they talk to some other piece of software to communicate information related to that parameter. The communication is expected to be slow and might involve blocking I/O network calls. An instance of the class is called from a Thread with this in mind.

If you expect your communicator subclass to always perform very quickly, the Thread will introduce overhead that may actually slow down overall system performance. Avoid this by creating a subclass of Hoodoo::Communicators::Fast instead.

Example: A communicator might be part of a logging scheme which talks to a network-based third party logging service. The parameter it expects would be a log message string.

IMPORTANT: If you use ActiveRecord in a slow communicator class, beware that your writer runs in a ruby Thread. Unless you take steps to prevent it, ActiveRecord will implicitly check out a connection which stays with your Thread forever. This steals a connection from the pool. To prevent this issue, you must use the following pattern:

def communicate( object )
  ActiveRecord::Base.connection_pool.with_connection do
    # ...Any AciveRecord code goes here...
  end
end

Code within the with_connection block uses a temporary connection from the pool which is returned once the block has finished processing. Even if exceptions occur within your ActiveRecord code, the connection is still correctly returned to the pool using the above approach.

Instance Method Summary collapse

Instance Method Details

#communicate(object) ⇒ Object

Communicate (possibly slowly) with the piece of external software for which your subclass is designed. Subclasses must implement this method. There is no need to call super in your implementation.

If a slow communicator can’t keep up with the incoming message rate, messages may be dropped. Implement #dropped if you want to detect this condition.

object

Parameter sent by the communication pool, in response to someone calling Hoodoo::Communicators::Pool#communicate with that value.



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# File 'lib/hoodoo/communicators/slow.rb', line 63

def communicate( object )
  raise( 'Subclasses must implement #communicate' )
end

#dropped(count) ⇒ Object

This method is called before #communicate if messages have been dropped prior to the one which #communicate is about to report. Should you care, your subclass can implement this method and take whatever action it wants (e.g. log that messages were discarded).

The default implementation does nothing; there is no need to call super in custom implementations.

count

Number of messages dropped between the previous call to #communicate and the call which is about to be made.



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# File 'lib/hoodoo/communicators/slow.rb', line 78

def dropped( count )
  # This Implementation Intentionally Left Blank
end