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
This test is broken right out of the box…
— FAIL: TestAgent (7.82s)
agent_test.go:77:
Error Trace: agent_test.go:77
agent_test.go:...
New
Hi everyone!
There is an error on the page 71 in the book “Programming machine learning from coding to depp learning” P. Perrotta. You c...
New
I thought that there might be interest in using the book with Rails 6.1 and Ruby 2.7.2. I’ll note what I needed to do differently here.
...
New
On the page xv there is an instruction to run bin/setup from the main folder. I downloaded the source code today (12/03/21) and can’t see...
New
This is as much a suggestion as a question, as a note for others.
Locally the SGP30 wasn’t available, so I ordered a SGP40. On page 53, ...
New
In general, the book isn’t yet updated for Phoenix version 1.6. On page 18 of the book, the authors indicate that an auto generated of ro...
New
When trying to run tox in parallel as explained on page 151, I got the following error:
tox: error: argument -p/–parallel: expected one...
New
Hey there,
I’m enjoying this book and have learned a few things alredayd. However, in Chapter 4 I believe we are meant to see the “>...
New
The markup used to display the uploaded image results in a Phoenix.LiveView.HTMLTokenizer.ParseError error.
lib/pento_web/live/product_l...
New
Skimming ahead, much of the following is explained in Chapter 3, but new readers (like me!) will hit a roadblock in Chapter 2 with their ...
New
Other popular topics
Algorithms and data structures are much more than abstract concepts. Mastering them enables you to write code that runs faster and more e...
New
Machine learning can be intimidating, with its reliance on math and algorithms that most programmers don't encounter in their regular wor...
New
Brace yourself for a fun challenge: build a photorealistic 3D renderer from scratch! In just a couple of weeks, build a ray tracer that r...
New
Bought the Moonlander mechanical keyboard. Cherry Brown MX switches. Arms and wrists have been hurting enough that it’s time I did someth...
New
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
Saw this on TikTok of all places! :lol:
Anyone heard of them before?
Lite:
New
Author Spotlight
Jamis Buck
@jamis
This month, we have the pleasure of spotlighting author Jamis Buck, who has written Mazes for Prog...
New
If you want a quick and easy way to block any website on your Mac using Little Snitch simply…
File > New Rule:
And select Deny, O...
New
Big O Notation can make your code faster by orders of magnitude. Get the hands-on info you need to master data structures and algorithms ...
New
Categories:
Sub Categories:
Popular Portals
- /elixir
- /rust
- /wasm
- /ruby
- /erlang
- /phoenix
- /keyboards
- /python
- /js
- /rails
- /security
- /go
- /swift
- /vim
- /clojure
- /java
- /emacs
- /haskell
- /svelte
- /onivim
- /typescript
- /kotlin
- /c-plus-plus
- /crystal
- /tailwind
- /react
- /gleam
- /ocaml
- /elm
- /flutter
- /ash
- /vscode
- /html
- /opensuse
- /zig
- /deepseek
- /centos
- /php
- /scala
- /react-native
- /lisp
- /textmate
- /sublime-text
- /nixos
- /debian
- /agda
- /deno
- /django
- /kubuntu
- /arch-linux
- /nodejs
- /spring
- /ubuntu
- /revery
- /manjaro
- /diversity
- /julia
- /lua
- /markdown
- /quarkus









