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

jeffmcompsci
Title: Design and Build Great Web APIs - typo “https://company-atk.herokuapp.com/2258ie4t68jv” (page 19, third bullet in URL list) Typo:...
New
GilWright
Working through the steps (checking that the Info,plist matches exactly), run the demo game and what appears is grey but does not fill th...
New
jesse050717
Title: Web Development with Clojure, Third Edition, pg 116 Hi - I just started chapter 5 and I am stuck on page 116 while trying to star...
New
raul
Hi Travis! Thank you for the cool book! :slight_smile: I made a list of issues and thought I could post them chapter by chapter. I’m rev...
New
raul
Page 28: It implements io.ReaderAt on the store type. Sorry if it’s a dumb question but was the io.ReaderAt supposed to be io.ReadAt? ...
New
adamwoolhether
I’m not quite sure what’s going on here, but I’m unable to have to containers successfully complete the Readiness/Liveness checks. I’m im...
New
digitalbias
Title: Build a Weather Station with Elixir and Nerves: Problem connecting to Postgres with Grafana on (page 64) If you follow the defau...
New
SlowburnAZ
Getting an error when installing the dependencies at the start of this chapter: could not compile dependency :exla, "mix compile" failed...
New
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

AstonJ
A thread that every forum needs! Simply post a link to a track on YouTube (or SoundCloud or Vimeo amongst others!) on a separate line an...
New
New
PragmaticBookshelf
Write Elixir tests that you can be proud of. Dive into Elixir’s test philosophy and gain mastery over the terminology and concepts that u...
New
AstonJ
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
Exadra37
Oh just spent so much time on this to discover now that RancherOS is in end of life but Rancher is refusing to mark the Github repo as su...
New
AstonJ
Saw this on TikTok of all places! :lol: Anyone heard of them before? Lite:
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
PragmaticBookshelf
Programming Ruby is the most complete book on Ruby, covering both the language itself and the standard library as well as commonly used t...
New
DevotionGeo
I have always used antique keyboards like Cherry MX 1800 or Cherry MX 8100 and almost always have modified the switches in some way, like...
New
PragmaticBookshelf
Author Spotlight: Peter Ullrich @PJUllrich Data is at the core of every business, but it is useless if nobody can access and analyze ...
New

Sub Categories: