Class: Whiteboard

Inherits:
Object
  • Object
show all
Defined in:
lib/appswarm/whiteboard.rb

Overview

Whiteboard is a pretty simple messaging class, that can be used for different (local) threads. It’s meant for use in storing incoming messages for later processing.

The normal usage looks like this:

w=Whiteboard.new
<spawn thread1 and thread2>
thread1: a=w.get(:myKey)
<thread1 is suspended, because myKey is not there>
thread2: w.put(:myKey,:myValue)
<thread1 is woken up and has a==:myValue>

This is NOT Possible:

Whiteboard.new.put(:myKey,:myValue)

because nobody’s listening for myKey

This is NOT possible either:

w=Whiteboard.new
thread1: w.get(:myValue) 
thread2: w.get(:myValue)

because thread1 is already waiting for this value

in practise this is not a problem, because the values are transaction-ids within node communication should not be duplicated.

Instance Method Summary collapse

Constructor Details

#initialize ⇒ Whiteboard

Returns a new instance of Whiteboard.



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# File 'lib/appswarm/whiteboard.rb', line 31

def initialize()
  @cvs={}
  @values={}
  @mutex=Mutex.new
end

Instance Method Details

#get(name, timeout = nil) ⇒ Object

waits for name to be put into the local store then returns the value



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# File 'lib/appswarm/whiteboard.rb', line 50

def get(name,timeout=nil)
  value=nil
  measureTime(7) {
    @mutex.synchronize {
      raise "Already value there" if @values[name]
      raise "Already listening" if @cvs[name]
      @cvs[name]=Thread.current
    }
    if timeout.nil?
      Thread.stop
    else
      # FIXME:wait until timeout
      Thread.stop
    end
    
    @mutex.synchronize {
      value=@values[name]
      @values.delete(name)
    }
  }
  value
end

#put(name, value) ⇒ Object

sends value directly to the listening thread waiting for name if there’s no waiting thread an exception is raised



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# File 'lib/appswarm/whiteboard.rb', line 39

def put(name,value)
  @mutex.synchronize {
    raise "Conflict in put" if @values[name]
    @values[name]=value
    raise "No one listening" if @cvs[name].nil?
    @cvs[name].wakeup
    @cvs.delete(name)
  }
end