Fiber for cooperative concurrency in Ruby - Mini Project: Build & Apply

Fiber for cooperative concurrency

📖 Scenario: You are building a simple program that uses Ruby Fiber to switch between two tasks cooperatively. This simulates how two workers take turns doing their jobs without interrupting each other.

🎯 Goal: Create two Fiber objects that print messages in turns, showing how cooperative concurrency works with Fiber.yield and Fiber.resume.

📋 What You'll Learn

Create two Fiber objects named fiber1 and fiber2.

Each fiber should print a message and then yield control.

Use a loop to resume each fiber alternately two times.

Print the messages exactly as specified.

💡 Why This Matters

🌍 Real World

Fibers let programs switch between tasks without waiting for one to finish, useful in games, network servers, or UI where tasks share time smoothly.

💼 Career

Understanding fibers helps in writing efficient Ruby programs that handle multiple tasks cooperatively, improving responsiveness and resource use.

1

Create two Fiber objects

Create two Fiber objects called fiber1 and fiber2. fiber1 should print "Fiber 1: Step 1" and then yield. fiber2 should print "Fiber 2: Step 1" and then yield.

Ruby

# Create fiber1 and fiber2 with initial print and yield
# Your code here

Hint

Use Fiber.new do ... end to create fibers. Inside each, print the message and call Fiber.yield to pause.

2

Add second steps inside fibers

Inside fiber1, after the first yield, print "Fiber 1: Step 2". Inside fiber2, after the first yield, print "Fiber 2: Step 2". Add these lines after the first Fiber.yield in each fiber.

Ruby

fiber1 = Fiber.new do
  puts "Fiber 1: Step 1"
  Fiber.yield
  # Your code here
end

fiber2 = Fiber.new do
  puts "Fiber 2: Step 1"
  Fiber.yield
  # Your code here
end

Hint

After Fiber.yield, add a puts line for the second step message inside each fiber.

3

Create a loop to resume fibers alternately

Create a 2.times do loop. Inside the loop, resume fiber1 and then resume fiber2 to switch between them.

Ruby

fiber1 = Fiber.new do
  puts "Fiber 1: Step 1"
  Fiber.yield
  puts "Fiber 1: Step 2"
end

fiber2 = Fiber.new do
  puts "Fiber 2: Step 1"
  Fiber.yield
  puts "Fiber 2: Step 2"
end

# Your code here to resume fibers alternately 2 times

Hint

Use 2.times do to repeat two times. Inside, call fiber1.resume then fiber2.resume.

4

Run the program and print the output

Run the program as is. The output should show the fibers printing their steps alternately. No extra code needed, just run the existing code.

Ruby

fiber1 = Fiber.new do
  puts "Fiber 1: Step 1"
  Fiber.yield
  puts "Fiber 1: Step 2"
end

fiber2 = Fiber.new do
  puts "Fiber 2: Step 1"
  Fiber.yield
  puts "Fiber 2: Step 2"
end

2.times do
  fiber1.resume
  fiber2.resume
end

# Run the program to see the output

Hint

Just run the program. You will see the fibers print their messages in turns twice.

Practice

1. What is the main purpose of using Fiber in Ruby?

easy

A. To pause and resume tasks manually for cooperative multitasking

B. To create multiple threads that run in parallel automatically

C. To speed up code by running it on multiple CPU cores

D. To handle database connections asynchronously

Solution

1. Step 1: Understand Fiber's role

   Fibers allow manual pausing and resuming of code execution, enabling cooperative multitasking.

2. Step 2: Differentiate from threads

   Unlike threads, Fibers do not run in parallel automatically; they require explicit control.

3. Final Answer:

   To pause and resume tasks manually for cooperative multitasking -> Option A

4. Quick Check:

   Fiber = manual pause/resume [OK]

Hint: Fibers pause and resume tasks manually, not parallel threads [OK]

Common Mistakes:

• Confusing Fibers with threads or parallelism
• Thinking Fibers run automatically in background
• Assuming Fibers speed up CPU usage

2. Which of the following is the correct way to create a Fiber in Ruby?

easy

A. fiber = Fiber.start { puts 'Hello' }

B. fiber = Fiber.new { puts 'Hello' }

C. fiber = Fiber.create { puts 'Hello' }

D. fiber = Fiber.run { puts 'Hello' }

Solution

1. Step 1: Recall Fiber creation syntax

   Ruby uses Fiber.new with a block to create a new Fiber.

2. Step 2: Check other options

   Methods like create, start, or run do not exist for Fiber creation.

3. Final Answer:

   fiber = Fiber.new { puts 'Hello' } -> Option B

4. Quick Check:

   Fiber creation = Fiber.new [OK]

Hint: Use Fiber.new with a block to create a Fiber [OK]

Common Mistakes:

• Using non-existent Fiber methods like create or start
• Forgetting to pass a block to Fiber.new
• Confusing Fiber with Thread syntax

3. What will be the output of the following Ruby code?

fiber = Fiber.new do
  puts 'Step 1'
  Fiber.yield
  puts 'Step 2'
end

fiber.resume
puts 'Between'
fiber.resume

medium

A. Step 2
Between
Step 1

B. Step 1
Step 2
Between

C. Between
Step 1
Step 2

D. Step 1
Between
Step 2

Solution

1. Step 1: Trace first resume call

   Calling fiber.resume runs until Fiber.yield, printing 'Step 1'.

2. Step 2: Trace code after first resume

   After yield, control returns to main, printing 'Between'.

3. Step 3: Trace second resume call

   Second fiber.resume resumes after yield, printing 'Step 2'.

4. Final Answer:

   Step 1 Between Step 2 -> Option D

5. Quick Check:

   Fiber.yield pauses, resume continues [OK]

Hint: Fiber.yield pauses; resume continues after yield [OK]

Common Mistakes:

• Assuming all code runs at first resume
• Confusing order of prints around yield
• Thinking yield stops Fiber permanently

4. Identify the error in this Fiber usage:

fiber = Fiber.new do
  puts 'Start'
  Fiber.yield
  puts 'End'
end

fiber.yield
fiber.resume

medium

A. Calling Fiber.yield outside a Fiber block causes an error

B. Fiber.resume must be called before Fiber.yield

C. Fiber.new requires a parameter for yield count

D. Fiber cannot print inside its block

Solution

1. Step 1: Check where Fiber.yield is called

   The code calls fiber.yield outside the Fiber block, which is invalid.

2. Step 2: Understand Fiber.yield usage

   Fiber.yield is a class method to pause current Fiber, not an instance method on Fiber objects.

3. Final Answer:

   Calling Fiber.yield outside a Fiber block causes an error -> Option A

4. Quick Check:

   Fiber.yield only inside Fiber block [OK]

Hint: Fiber.yield is called inside Fiber block only [OK]

Common Mistakes:

• Calling fiber.yield instead of Fiber.yield
• Expecting Fiber.resume before yield call
• Thinking Fiber.new needs parameters for yield

5. Given two Fibers that alternate printing numbers, what is the output of this code?

fiber1 = Fiber.new do
  3.times do |i|
    puts "Fiber1: #{i}"
    Fiber.yield
  end
end

fiber2 = Fiber.new do
  3.times do |i|
    puts "Fiber2: #{i}"
    Fiber.yield
  end
end

while fiber1.alive? || fiber2.alive?
  fiber1.resume if fiber1.alive?
  fiber2.resume if fiber2.alive?
end

hard

A. Fiber2: 0
Fiber1: 0
Fiber2: 1
Fiber1: 1
Fiber2: 2
Fiber1: 2

B. Fiber1: 0
Fiber1: 1
Fiber1: 2
Fiber2: 0
Fiber2: 1
Fiber2: 2

C. Fiber1: 0
Fiber2: 0
Fiber1: 1
Fiber2: 1
Fiber1: 2
Fiber2: 2

D. Fiber1: 0
Fiber2: 0
Fiber2: 1
Fiber1: 1
Fiber1: 2
Fiber2: 2

Solution

1. Step 1: Understand Fiber alternation

   Each Fiber prints a number then yields, pausing itself.

2. Step 2: Trace the while loop

   The loop resumes fiber1 then fiber2 alternately while they are alive.

3. Step 3: Follow output order

   Output alternates: Fiber1:0, Fiber2:0, Fiber1:1, Fiber2:1, Fiber1:2, Fiber2:2.

4. Final Answer:

   Fiber1: 0 Fiber2: 0 Fiber1: 1 Fiber2: 1 Fiber1: 2 Fiber2: 2 -> Option C

5. Quick Check:

   Fibers alternate resume and yield [OK]

Hint: Fibers alternate resume and yield to interleave output [OK]

Common Mistakes:

• Assuming one Fiber runs completely before the other
• Mixing order of Fiber resumes
• Forgetting Fiber.yield pauses execution