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Recently I have been refactoring some code so that various computed results are saved in a memcached cache to improve performance.

A common cache idiom is:

1. Compute cache key
2. look up key in cache
3. if value found, return it
4. else, run some code to generate the required value
5. save the generated value in the cache
6. return the value

It's quite awkward to have that code repeated all over your app, so I hit upon the idea of passing a block to Cache#get() which would be used to compute the value if the key wasn't found in the cache.

module Cache
  class << self
    alias _get get
  end

  def self.get(key, expiry = 0)
    value = _get(key)
    if value.nil? && block_given?
      value = yield
      put(key, value, expiry)
    end
    value
  end
end

cache_key = "#{some}/#{vars}"
value = Cache.get cache_key
unless value
  value = a_SOAP_call_that_takes_a_few_seconds()
  Cache.put cache_key, value, 10.minutes
end
value

Cache.get("#{some}/#{vars}", 10.minutes) do
  a_SOAP_call_that_takes_a_few_seconds()
end

Mac OS X 10.4 comes with ruby 1.8.2, it seems to have a problem with OpenSSL which causes switchtower to hang when trying to connect to your server.

You can download the source code to Ruby 1.8.3, compile it and install it, but you’ll start getting weird errors in gem when you try to install some libraries.

The solution turned out to be to compile Ruby slightly differently. You need to pass some flags to configure:

./configure --enable-shared --enable-pthread

After configuring it, makeing it, and running sudo make install, I had what seemed to be a working Ruby installation. It installs to /usr/local/bin which is already in my path. Executing hash -r causes bash to re-scan the path, after which executing ruby -v correctly reports

ruby 1.8.3 (2005-09-21) [powerpc-darwin8.3.0]

After that I installed RubyGems-0.8.11 and the rails and switchtower gems, including all dependencies. The installation worked fine, and so did switchtower when I tested it.

I didn’t even need to remove Apple’s Ruby install.

If you do want to remove Apple’s installation of Ruby, you’ll want to back up and delete the following files and directories:

/usr/bin/erb
/usr/bin/irb
/usr/bin/rdoc
/usr/bin/ri
/usr/bin/ruby
/usr/bin/testrb
/usr/bin/gem
/usr/bin/gem_server
/usr/bin/gemwhich
/usr/bin/rake

/usr/lib/ruby/
/usr/lib/libruby.1.dylib
/usr/lib/libruby.dylib

/usr/share/ri/