sinaru
Programming Ruby 3.2 (5th Edition): page 189 page_to_fetch variable question
There is an example of using Threads on page 188:
require "net/http"
pages = %w[www.rubycentral.org www.pragprog.com www.google.com]
threads = pages.map do |page_to_fetch|
Thread.new(page_to_fetch) do |url|
puts "inside thread id:#{url.object_id}, value:#{url}"
http = Net::HTTP.new(url, 80)
print "Fetching: #{url}\n"
response = http.get("/")
end
end
threads.each { |thread| thread.join }
print "We're done here!\n"
Then on page 189 5th paragraph, it says:
The first thread gets started, and page_to_fetch is set to “www.rubycentral.org”. The meantime, the loop creating the threads is still running. The second time around, page_to_fetch gets set to “pgragprog.com”. If the first thread hasn’t yet finished using the page_to_fetch variable, it’ll suddenly start using this new value.
As I understand the last sentence here is wrong.
page_to_fetch is going to point to the string objects during the loop so no thread will point to the same string.
See below code with additional put statements and the output. Note that object ID is always different:
require "net/http"
pages = %w[www.rubycentral.org www.pragprog.com www.google.com]
threads = pages.map do |page_to_fetch|
puts "outside thread page_to_fetch id:#{page_to_fetch.object_id}, value:#{page_to_fetch}"
Thread.new(page_to_fetch) do |url|
puts "inside thread url id:#{url.object_id}, value:#{url}"
http = Net::HTTP.new(url, 80)
print "Fetching: #{url}\n"
response = http.get("/")
print "Got #{url}: #{response.message}\n"
end
end
threads.each { |thread| thread.join }
print "We're done here!\n"
output:
outside thread page_to_fetch id:60, value:www.rubycentral.org
outside thread page_to_fetch id:80, value:www.pragprog.com
outside thread page_to_fetch id:100, value:www.google.com
inside thread url id:60, value:www.rubycentral.org
Fetching: www.rubycentral.org
inside thread url id:100, value:www.google.com
Fetching: www.google.com
inside thread url id:80, value:www.pragprog.com
Fetching: www.pragprog.com
Got www.google.com: OK
Got www.rubycentral.org: Found
Got www.pragprog.com: Moved Permanently
We're done here!
Popular Pragmatic Bookshelf topics
Python Testing With Pytest - Chapter 2, warnings for “unregistered custom marks”
While running the smoke tests in Chapter 2, I get these...
New
Many tasks_proj/tests directories exist in chapters 2, 3, 5 that have tests that use the custom markers smoke and get, which are not decl...
New
Hello Brian,
I have some problems with running the code in your book. I like the style of the book very much and I have learnt a lot as...
New
your book suggests to use Image.toByteData() to convert image to bytes, however I get the following error: "the getter ‘toByteData’ isn’t...
New
Title: Hands-On Rust (Chap 8 (Adding a Heads Up Display)
It looks like
.with_simple_console_no_bg(SCREEN_WIDTH*2, SCREEN_HEIGHT*2...
New
A Common-Sense Guide to Data Structures and Algorithms, Second Edition by Jay Wengrow @jaywengrow
Hi,
I have the paperback version of t...
New
Hi,
I completed chapter 6 but am getting the following error when running:
thread 'main' panicked at 'Failed to load texture: IoError(O...
New
It seems the second code snippet is missing the code to set the current_user:
current_user: Accounts.get_user_by_session_token(session["...
New
Hi all,
currently I wonder how the Tailwind colours work (or don’t work).
For example, in app/views/layouts/application.html.erb I have...
New
Hi, I’ve got a question about the implementation of PubSub when using a Phoenix.Socket.Transport behaviour rather than channels.
Before ...
New
Other popular topics
Reading something? Working on something? Planning something? Changing jobs even!?
If you’re up for sharing, please let us know what you’...
New
poll
poll
Be sure to check out @Dusty’s article posted here: An Introduction to Alternative Keyboard Layouts It’s one of the best write-...
New
I’ve been hearing quite a lot of comments relating to the sound of a keyboard, with one of the most desirable of these called ‘thock’, he...
New
Thanks to @foxtrottwist’s and @Tomas’s posts in this thread: Poll: Which code editor do you use? I bought Onivim! :nerd_face:
https://on...
New
This looks like a stunning keycap set :orange_heart:
A LEGENDARY KEYBOARD LIVES ON
When you bought an Apple Macintosh computer in the e...
New
Do the test and post your score :nerd_face:
:keyboard:
If possible, please add info such as the keyboard you’re using, the layout (Qw...
New
In case anyone else is wondering why Ruby 3 doesn’t show when you do asdf list-all ruby :man_facepalming: do this first:
asdf plugin-upd...
New
Intensively researching Erlang books and additional resources on it, I have found that the topic of using Regular Expressions is either c...
New
Hi folks,
I don’t know if I saw this here but, here’s a new programming language, called Roc
Reminds me a bit of Elm and thus Haskell. ...
New
I am trying to crate a game for the Nintendo switch, I wanted to use Java as I am comfortable with that programming language. Can you use...
New
Categories:
Sub Categories:
Popular Portals
- /elixir
- /rust
- /wasm
- /ruby
- /erlang
- /phoenix
- /keyboards
- /python
- /js
- /rails
- /security
- /go
- /swift
- /vim
- /clojure
- /emacs
- /haskell
- /java
- /svelte
- /onivim
- /typescript
- /kotlin
- /c-plus-plus
- /crystal
- /tailwind
- /react
- /gleam
- /ocaml
- /flutter
- /elm
- /vscode
- /ash
- /html
- /opensuse
- /zig
- /centos
- /deepseek
- /php
- /scala
- /react-native
- /lisp
- /sublime-text
- /textmate
- /nixos
- /debian
- /agda
- /django
- /kubuntu
- /deno
- /arch-linux
- /nodejs
- /ubuntu
- /revery
- /manjaro
- /spring
- /lua
- /diversity
- /julia
- /markdown
- /c








