Mixin methods for local and remote Gem::Command options.

Raised in case of a stack overflow.

def me_myself_and_i
  me_myself_and_i
end
me_myself_and_i

raises the exception:

SystemStackError: stack level too deep

Coverage provides coverage measurement feature for Ruby. This feature is experimental, so these APIs may be changed in future.

Usage

1. require “coverage”

2. do Coverage.start

3. require or load Ruby source file

4. Coverage.result will return a hash that contains filename as key and coverage array as value. A coverage array gives, for each line, the number of line execution by the interpreter. A nil value means coverage is disabled for this line (lines like else and end).

Example

[foo.rb]
s = 0
10.times do |x|
  s += x
end

if s == 45
  p :ok
else
  p :ng
end
[EOF]

require "coverage"
Coverage.start
require "foo.rb"
p Coverage.result  #=> {"foo.rb"=>[1, 1, 10, nil, nil, 1, 1, nil, 0, nil]}

Raised when an unknown conversion error occurs.

Raised when a conversion failure occurs.

Raised by Encoding and String methods when a transcoding operation fails.

Represents an error communicating via HTTP.

Raised by exit to initiate the termination of the script.

SystemCallError is the base class for all low-level platform-dependent errors.

The errors available on the current platform are subclasses of SystemCallError and are defined in the Errno module.

File.open("does/not/exist")

raises the exception:

Errno::ENOENT: No such file or directory - does/not/exist

Use the Monitor class when you want to have a lock object for blocks with mutual exclusion.

require 'monitor'

lock = Monitor.new
lock.synchronize do
  # exclusive access
end

PStore implements a file based persistence mechanism based on a Hash. User code can store hierarchies of Ruby objects (values) into the data store file by name (keys). An object hierarchy may be just a single object. User code may later read values back from the data store or even update data, as needed.

The transactional behavior ensures that any changes succeed or fail together. This can be used to ensure that the data store is not left in a transitory state, where some values were updated but others were not.

Behind the scenes, Ruby objects are stored to the data store file with Marshal. That carries the usual limitations. Proc objects cannot be marshalled, for example.

Usage example:

require "pstore"

# a mock wiki object...
class WikiPage
  def initialize( page_name, author, contents )
    @page_name = page_name
    @revisions = Array.new

    add_revision(author, contents)
  end

  attr_reader :page_name

  def add_revision( author, contents )
    @revisions << { :created  => Time.now,
                    :author   => author,
                    :contents => contents }
  end

  def wiki_page_references
    [@page_name] + @revisions.last[:contents].scan(/\b(?:[A-Z]+[a-z]+){2,}/)
  end

  # ...
end

# create a new page...
home_page = WikiPage.new( "HomePage", "James Edward Gray II",
                          "A page about the JoysOfDocumentation..." )

# then we want to update page data and the index together, or not at all...
wiki = PStore.new("wiki_pages.pstore")
wiki.transaction do  # begin transaction; do all of this or none of it
  # store page...
  wiki[home_page.page_name] = home_page
  # ensure that an index has been created...
  wiki[:wiki_index] ||= Array.new
  # update wiki index...
  wiki[:wiki_index].push(*home_page.wiki_page_references)
end                   # commit changes to wiki data store file

### Some time later... ###

# read wiki data...
wiki.transaction(true) do  # begin read-only transaction, no changes allowed
  wiki.roots.each do |data_root_name|
    p data_root_name
    p wiki[data_root_name]
  end
end

Transaction modes

By default, file integrity is only ensured as long as the operating system (and the underlying hardware) doesn’t raise any unexpected I/O errors. If an I/O error occurs while PStore is writing to its file, then the file will become corrupted.

You can prevent this by setting pstore.ultra_safe = true. However, this results in a minor performance loss, and only works on platforms that support atomic file renames. Please consult the documentation for ultra_safe for details.

Needless to say, if you’re storing valuable data with PStore, then you should backup the PStore files from time to time.

Helper module for easily defining exceptions with predefined messages.

Usage

1.

class Foo
  extend Exception2MessageMapper
  def_e2message ExistingExceptionClass, "message..."
  def_exception :NewExceptionClass, "message..."[, superclass]
  ...
end

2.

module Error
  extend Exception2MessageMapper
  def_e2message ExistingExceptionClass, "message..."
  def_exception :NewExceptionClass, "message..."[, superclass]
  ...
end
class Foo
  include Error
  ...
end

foo = Foo.new
foo.Fail ....

3.

module Error
  extend Exception2MessageMapper
  def_e2message ExistingExceptionClass, "message..."
  def_exception :NewExceptionClass, "message..."[, superclass]
  ...
end
class Foo
  extend Exception2MessageMapper
  include Error
  ...
end

Foo.Fail NewExceptionClass, arg...
Foo.Fail ExistingExceptionClass, arg...

In concurrent programming, a monitor is an object or module intended to be used safely by more than one thread. The defining characteristic of a monitor is that its methods are executed with mutual exclusion. That is, at each point in time, at most one thread may be executing any of its methods. This mutual exclusion greatly simplifies reasoning about the implementation of monitors compared to reasoning about parallel code that updates a data structure.

You can read more about the general principles on the Wikipedia page for Monitors

Examples

Simple object.extend

require 'monitor.rb'

buf = []
buf.extend(MonitorMixin)
empty_cond = buf.new_cond

# consumer
Thread.start do
  loop do
    buf.synchronize do
      empty_cond.wait_while { buf.empty? }
      print buf.shift
    end
  end
end

# producer
while line = ARGF.gets
  buf.synchronize do
    buf.push(line)
    empty_cond.signal
  end
end

The consumer thread waits for the producer thread to push a line to buf while buf.empty?. The producer thread (main thread) reads a line from ARGF and pushes it into buf then calls empty_cond.signal to notify the consumer thread of new data.

Simple Class include

require 'monitor'

class SynchronizedArray < Array

  include MonitorMixin

  def initialize(*args)
    super(*args)
  end

  alias :old_shift :shift
  alias :old_unshift :unshift

  def shift(n=1)
    self.synchronize do
      self.old_shift(n)
    end
  end

  def unshift(item)
    self.synchronize do
      self.old_unshift(item)
    end
  end

  # other methods ...
end

SynchronizedArray implements an Array with synchronized access to items. This Class is implemented as subclass of Array which includes the MonitorMixin module.