sinaru

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. :thinking: 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!

Where Next?

Popular Pragmatic Bookshelf topics Top

jon
Some minor things in the paper edition that says “3 2020” on the title page verso, not mentioned in the book’s errata online: p. 186 But...
New
brianokken
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
jeffmcompsci
Title: Design and Build Great Web APIs - typo “https://company-atk.herokuapp.com/2258ie4t68jv” (page 19, third bullet in URL list) Typo:...
New
simonpeter
When I try the command to create a pair of migration files I get an error. user=> (create-migration "guestbook") Execution error (Ill...
New
mikecargal
Title: Hands-On Rust (Chapter 11: prefab) Just played a couple of amulet-less games. With a bit of debugging, I believe that your can_p...
New
JohnS
I can’t setup the Rails source code. This happens in a working directory containing multiple (postgres) Rails apps. With: ruby-3.0.0 s...
New
jeremyhuiskamp
Title: Web Development with Clojure, Third Edition, vB17.0 (p9) The create table guestbook syntax suggested doesn’t seem to be accepted ...
New
curtosis
Running mix deps.get in the sensor_hub directory fails with the following error: ** (Mix) No SSH public keys found in ~/.ssh. An ssh aut...
New
oaklandgit
Hi, I completed chapter 6 but am getting the following error when running: thread 'main' panicked at 'Failed to load texture: IoError(O...
New
dachristenson
I’ve got to the end of Ch. 11, and the app runs, with all tabs displaying what they should – at first. After switching around between St...
New

Other popular topics Top

wolf4earth
@AstonJ prompted me to open this topic after I mentioned in the lockdown thread how I started to do a lot more for my fitness. https://f...
New
AstonJ
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
AstonJ
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
dimitarvp
Small essay with thoughts on macOS vs. Linux: I know @Exadra37 is just waiting around the corner to scream at me “I TOLD YOU SO!!!” but I...
New
AstonJ
Saw this on TikTok of all places! :lol: Anyone heard of them before? Lite:
New
AstonJ
Was just curious to see if any were around, found this one: I got 51/100: Not sure if it was meant to buy I am sure at times the b...
New
PragmaticBookshelf
Author Spotlight Mike Riley @mriley This month, we turn the spotlight on Mike Riley, author of Portable Python Projects. Mike’s book ...
New
New
NewsBot
Node.js v22.14.0 has been released. Link: Release 2025-02-11, Version 22.14.0 'Jod' (LTS), @aduh95 · nodejs/node · GitHub
New
RobertRichards
Hair Salon Games for Girls Fun Girls Hair Saloon game is mainly developed for kids. This game allows users to select virtual avatars to ...
New

Sub Categories: