RubyTapas #134 - #140

134 Rake Clean

★★

コンバート

sh "ebook-convert book.html #{t.name}"
sh "kindlegen book.epub -o #{t.name}"

Rake clean task

require "rake/clean"

CLEAN                           # => []
CLEAN.include("book.html")

CLOBBER

CLOBBER << "book.epub"
CLOBBER << "book.mobi"


$ rake clobber

clobber first executes the clean task

135 Rake Multitask

★

CLEAN FileList

LISTINGS   = FileList["listings/*"]
HIGHLIGHTS = LISTINGS.ext(".html")
CLEAN.include(HIGHLIGHTS)

rake内で task -> multitask

-j はプロセス数

multitask :highlight => HIGHLIGHTS
$ time rake -j 4

multitaskしなくても -m でできる

task :highlight => HIGHLIGHTS
$ time rake -m

136 Dead Thread

★

silent failure 問題があってもエラーにならずに気付かない
次のフラグを追加

Thread.abort_on_exception = true

debug

$DEBUG = true

timeout 通常は使うべきでない

require "timeout"
Timeout.timeout(3) do

multi threadはsilent failureを起こしやすい

137 Mutex

？

exclusivity

threadはjoinで起動

threads.each(&:join)

Mutex

Thread.exclusive

↓

@lock  = Mutex.new
...
@lock.synchronize

concurrency難い

138 Condition Variable

？

previous episode : inefficient and CPU-intensive way for a thread to wait

only wait if the items array is empty

@item_available = ConditionVariable.new
...
@item_available.signal
@item_available.wait(@lock) if @items.empty?

now have a queue which is largely equivalent in functionality to Ruby's standard library Queue

前のエピソードより断然速い

139 Timed Queue

？

one second is an eternity in CPU terms

waitとかは1じゃなくて少数を使うべき

cv.wait(l, 0.05)

今まで必要でやったこともないし、あまり興味のあるジャンルじゃない

ただベンチマーク的な物は好き

140 Threads are Hard

？

shutdown

trap("INT") do
  $shutdown = true
end

BUGを直す

deadline   = timeout == :never ? :never : Time.now + timeout
...
loop do
    cv_timeout = timeout == :never ? nil : deadline - Time.now
...
elsif deadline == :never || deadline > Time.now

Nightmare