Class: Amp::Journal

Inherits:
Object show all
Defined in:
lib/amp/repository/journal.rb

Overview

Provides a journal interface so when a large number of transactions are occurring, and any one could fail, we can rollback the changes.

Constant Summary collapse

DEFAULT_OPTS = 
{:reporter => StandardErrorReporter, :after_close => nil}

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(reporter = StandardErrorReporter, journal = "journal#{rand(10000)}", createmode = nil, &after_close) ⇒ Journal

Initializes the journal to get ready for some transactions.

Parameters:

  • reporter (#report) (defaults to: StandardErrorReporter) —

    an object that will keep track of any alerts we have to send out. Must respond to #report.

  • journal (String) (defaults to: "journal#{rand(10000)}") —

    the path to the journal file to use

  • createmode (Integer) (defaults to: nil) —

    An octal number that sets the filemode of the journal file we’ll be using

  • after_close (Proc) —

    A proc to call (with no args) after we close (finish) the transaction.



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# File 'lib/amp/repository/journal.rb', line 42

def initialize(reporter=StandardErrorReporter, journal="journal#{rand(10000)}", createmode=nil, &after_close)      
  @count = 1
  @reporter = reporter
  @after_close = after_close
  @entries = []
  @map = {}
  @journal_file = journal
  
  @file = open(@journal_file, "w")
  
  FileUtils.chmod(createmode & 0666, @journal_file) unless createmode.nil?
end

Instance Attribute Details

#after_close ⇒ Object

Returns the value of attribute after_close.



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# File 'lib/amp/repository/journal.rb', line 14

def after_close
  @after_close
end

#journal ⇒ Object

Returns the value of attribute journal.



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# File 'lib/amp/repository/journal.rb', line 14

def journal
  @journal
end

#report ⇒ Object

Returns the value of attribute report.



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# File 'lib/amp/repository/journal.rb', line 14

def report
  @report
end

Class Method Details

.rollback(file) ⇒ Object

If we crashed during an abort, the journal file is gonna be sitting aorund somewhere. So, we should rollback any changes it left lying around.

Parameters:

  • file (String) —

    the journal file to use during the rollback



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# File 'lib/amp/repository/journal.rb', line 179

def self.rollback(file)
  files = {}
  fp = open(file)
  fp.each_line do |line|
    file, offset = line.split("\0")
    files[file] = offset.to_i
  end
  fp.close
  files.each do |file, offset|
    if o > 0
      fp = open(file, "a")
      fp.truncate o.to_i
      fp.close
    else
      fp = open(f)
      fn = fp.path
      fp.close
      FileUtils.safe_unlink fn
    end
  end
  FileUtils.safe_unlink file
end

.start(file, opts = DEFAULT_OPTS) ⇒ Amp::Journal

Returns:



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# File 'lib/amp/repository/journal.rb', line 18

def self.start(file, opts=DEFAULT_OPTS)
  journal = Journal.new opts[:reporter], file, &opts[:after_close]
  
  if block_given?
    begin
      yield journal
    ensure
      journal.close
    end
  end
  
  journal
end

Instance Method Details

#abort ⇒ Object

Abort, abort! abandon ship! This rolls back any changes we’ve made during the current journalling session.



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# File 'lib/amp/repository/journal.rb', line 157

def abort
  return unless @entries && @entries.any?
  @reporter.report "transaction abort!\n"
  @entries.each do |hash|
    file, offset = hash[:file], hash[:offset]
    begin
      fp = open(File.join(".hg","store",file), "a")
      fp.truncate offset
      fp.close
    rescue
      @reporter.report "Failed to truncate #{File.join(".hg","store",file)}\n"
    end
  end
  @entries = []
  @reporter.report "rollback completed\n"
end

#add_entry(array) ⇒ Object Also known as: <<

Adds an entry to the journal. Since all our files are just being appended to all the time, all we really need is to keep track of how long the file was when we last knew it to be safe. In other words, if the file started off at 20 bytes, then an error happened, we just truncate it to 20 bytes.

All params should be contained in the array

Parameters:

  • file —

    the name of the file we’re modifying and need to track

  • offset —

    the length of the file we’re storing

  • data —

    any extra data to hold onto



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# File 'lib/amp/repository/journal.rb', line 77

def add_entry(array)
  file, offset, data = array[0], array[1], array[2]
  return if @map[file]
  @entries << {:file => file, :offset => offset, :data => data}
  @map[file] = @entries.size - 1
  
  # tell the journal how to truncate this revision
  @file.write("#{file}\0#{offset}\n")
  @file.flush
end

#close ⇒ Object

Closes up the journal. Will call the after_close proc passed during instantiation.



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# File 'lib/amp/repository/journal.rb', line 141

def close
  @count -= 1
  return if @count != 0
  @file.close
  @entries = []
  if @after_close
    @after_close.call
  else
    FileUtils.safe_unlink(@journal_file)
  end
  @journal_file = nil
end

#delete ⇒ Object

Kills the journal - used when shit goes down and we gotta give up on the transactions.



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# File 'lib/amp/repository/journal.rb', line 58

def delete
  if @journal_file
    abort if @entries.any?
    @file.close
    FileUtils.safe_unlink @journal_file
  end
end

#find_file(file) ⇒ Hash Also known as: find

Finds the entry for a given file’s path

Parameters:

  • file (String) —

    the path to the file

Returns:

  • (Hash) —

    A hash with the values :file, :offset, and :data, as they were when they were stored by #add_entry or #update



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# File 'lib/amp/repository/journal.rb', line 97

def find_file(file)
  return @entries[@map[file]] if @map[file]
  nil
end

#nest ⇒ Object

No godly idea what this is for



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# File 'lib/amp/repository/journal.rb', line 127

def nest
  @count += 1
  self
end

#replace(file, offset, data = nil) ⇒ Object Also known as: update

Updates an entry’s data, based on the filename. The file must already have been journaled.

Parameters:

  • file (String) —

    the file to update

  • offset (Fixnum) —

    the new offset to store

  • data (String) (defaults to: nil) —

    the new data to store

Raises:

  • (IndexError) 


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# File 'lib/amp/repository/journal.rb', line 113

def replace(file, offset, data=nil)
  raise IndexError.new("journal lookup failed #{file}") unless @map[file]
  index = @map[file]
  @entries[index] = {:file => file, :offset => offset, :data => data}
  @file.write("#{file}\0#{offset}\n")
  @file.flush
end

#running? ⇒ Boolean

Is the journal running right now?

Returns:



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# File 'lib/amp/repository/journal.rb', line 134

def running?
  @count > 0
end