Shugo's Blog

FizzBuzz with Sather like loop

Sat, 25 Aug 2007 08:06:00 JST

num = (1..100).each
fizz = ([""] * 2 + ["Fizz"]).cycle
buzz = ([""] * 4 + ["Buzz"]).cycle
loop do
  n = num.next
  puts (fizz.next + buzz.next).sub(/\A\z/) { n }
end

Graceful Restart with mod_fcgid

Sat, 25 Aug 2007 00:39:00 JST

I tried to restart Rails application gracefully (apachectl graceful) with mod_fcgid, but I couldn't get a response on graceful restart.

The problems are:

mod_fcgid sends SIGTERM to FastCGI processes on graceful restart, but Rails FastCGI processes exit as soon as it's received SIGTERM (Rails FastCGI processes stop gracefully on SIGUSR1, not SIGTERM).
Apache child processes exit on SIGUSR1 with mod_fcgid, as soon as it's received a signal.

I created a patch to fix these problems, but I'm not sure....

Sather like loop

Fri, 24 Aug 2007 22:15:00 JST

Sather like loop is available in the SVN head.

e1 = [1,2,3,4,5].each
e2 = ["a","b","c","d","e"].each

loop do
  p [e1.next, e2.next]
end

It's cool, isn't it?

Building MySQL/Ruby on mswin32

Mon, 25 Sep 2006 06:30:00 JST

I created a patch to build MySQL/Ruby on mswin32. With this patch, just type:

> ruby extconf.rb --with-opt-include=../mysql-4.1.21-win32/include \
                  --with-opt-lib=../mysql-4.1.21-win32/lib/opt
> nmake

Then you'll get mysql.so. Really easy.

If libmysql.dll is built by VC7 or later, there may be a problem with GC. It depends on whether MySQL/Ruby releases memory allocated by libmysql.dll using free()/xfree() or not.

to_json hack for Safari

Sat, 15 Jul 2006 17:30:00 JST

I found the reason why multibyte characters are encoded in to_json. Safari can't handle UTF-8 strings in text/javascript correctly:(

Here is new code:

class String
  JSON_ESCAPED = {
     "\010" =>  '\b',
     "\f" =>    '\f',
     "\n" =>    '\n',
     "\r" =>    '\r',
     "\t" =>    '\t',
     '"' =>     '\"',
     '\\' =>    '\\\\'
  }

  def to_json
    return '"' + gsub(/[\010\f\n\r\t"\\]/) { |s|
      JSON_ESCAPED[s]
    }.gsub(/([\xC0-\xDF][\x80-\xBF]|
             [\xE0-\xEF][\x80-\xBF]{2}|
             [\xF0-\xF7][\x80-\xBF]{3})+/ux) { |s|
      s.unpack("U*").pack("n*").unpack("H*")[0].gsub(/.{4}/, '\\\\u\&')
    } + '"'
  end
end

I created a patch for ActiveSupport (trac of Rails is down, so I can't attach this patch to the ticket).

to_json-2.diff

to_json too slow

Tue, 11 Jul 2006 12:51:00 JST

I felt my application slow yesterday and profiled it. RJS is very useful, but it seems to be slow.

Thanks to Charlies's ruby-prof (it doesn't belongs to me any more and has fascinating call graph support), I found the bottleneck. It was Object#to_json.

The original code is here:

define_encoder String do |string|
  returning value = '"' do
    string.each_char do |char|
      value << case
      when char == "\010":  '\b'
      when char == "\f":    '\f'
      when char == "\n":    '\n'
      when char == "\r":    '\r'
      when char == "\t":    '\t'
      when char == '"':     '\"'
      when char == '\':    '\\'
      when char.length > 1: "\u#{'%04x' % char.unpack('U').first}"
      else;                 char
      end
    end
    value << '"'
  end
end

Ruby can't handle characters fast, so this code is very slow. You'd should use builtin methods such as String#gsub to handle multiple characters at once.

I put the following code into config/environment.rb, and it looks quite fast:)

class String
  JSON_ESCAPED = {
     "\010" =>  '\b',
     "\f" =>    '\f',
     "\n" =>    '\n',
     "\r" =>    '\r',
     "\t" =>    '\t',
     '"' =>     '\"',
     '\' =>    '\\'
  }

  def to_json
    return '"' + gsub(/[\010\f\n\r\t"\]/) { |s|
      JSON_ESCAPED[s]
    } + '"'
  end
end

Then I posted a patch to a related ticket.

If there is any reason to encode multibyte characters, more hacks are needed. I think the best way is to encode multiple multibyte characters at once using String#gsub and String#unpack, Array#pack.

Apache::RailsDispatcher supports Rails 1.1

Wed, 24 May 2006 22:31:00 JST

Apache::RailsDispatcher in the SVN trunk of mod_ruby supports Rails 1.1 now:) I will release mod_ruby-1.2.6 soon.

But I can't run typo on it yet:(

RubyKaigi is Sold Out!

Thu, 11 May 2006 06:35:00 JST

Tickets of RubyKaigi are sold out in a few hours!

I'll talk about meta programming features of Ruby. See you in Tokyo.

PessmisticLocking

Thu, 11 May 2006 06:35:00 JST

PessimisticLocking provides row-level pessimistic locking using SELECT FOR UPDATE.

You can specify the new option :lock of ActiveRecord::Base.find() to lock rows:

Account.transaction do
  shugo = Account.find(:first, :conditions => "name = 'shugo'", :lock => true)
  yuko = Account.find(:first, :conditions => "name = 'yuko'", :lock => true)
  shugo.balance -= 100
  shugo.save
  yuko.balance += 100
  yuko.save
end

Or you can also use ActiveRecord::Base#lock() instead:

Account.transaction do
  accounts = Account.find(:all, :conditions => ...)
  account1 = accounts.detect { |account| ... }
  account2 = accounts.detect { |account| ... }
  account1.lock
  account2.lock
  account1.balance -= 100
  account1.save
  account2.balance += 100
  account2.save
end

The latter way may be better if you don't need lock all SELECTed rows.

Japanese translation of AWDwR

Tue, 21 Feb 2006 15:23:00 JST

The Japanese translation of Agile Web Development with Rails will be available on Sat Feb 25:)