Changes 9/26/14

Ruby:

• Looked into ruby's Queue object
• Saw that the method Queue#pop, which returns the first element and removes it from the queue, is blocking, meaning that it will block its thread if the queue is empty while waiting for a value to return.
• This is great for me, because I was looking for a way to have a thread that could pause itself while waiting for files to download and resume itself once those files are downloaded
• I rewrote my threading test to use the queue object, and it ended up being much more straight-forward and probably more thread safe as well
• 
  
• In the code marked 1. in the code section I have an excerpt I came up with to utilize Queue#pop.  This code is intended to be run in a method in a separate thread, and will either parse items if there are any in the queue or do nothing while waiting for more to be added
• END_PARSE_SYM is a constant value that is added to the queue when another method, Parser#finish, is called.  As you can see by the code, this signals that there are no more files for the queue to wait for, and therefore the infinite while loop is exited.
• 
  
• One choice I made while writing my Parser class was to keep the thread behavior up to the code calling the Parser#parse method, meaning that Parser doesn't actually have any multithreading code.
• Instead, you must call something like what is listed in code excerpt 2.  The statement within the { } runs in a separate thread, which is good, because in its current form, this method blocks its thread due to the Queue#pop statement being called on an empty queue within Parser#parse
• A side effect of this is that if you call parser.parse in the main thread, it throws a deadlock exception, because the @queue.pop statement is now blocking the main thread, so nothing will ever happen.  I think this is acceptable behavior though, because Parser#parse really should never be called in the main thread anyway.
• I will look into other ways to throw an exception if Parser#parse is being called in the main thread

Code:

1.

def parse
  ...
  while true do
    puts "Waiting for queue" if @queue.empty?
    file = @queue.pop
    break if file == END_PARSE_SYM
    <... parse code here >
  end
end

2.

thread = Thread.new { parser.parse }