Concurrency Basics

Fiber Resume

A fiber pauses and resumes work at explicit yield points.

fiber Fibers are cooperative: code switches between the caller and the fiber only when `yield` and `resume` are used.

Fiber Resume

start
fiber_resume.rb
Replay: real traced execution (multi-file project)
start = 2

sequence = Fiber.new do
  first = start
  Fiber.yield(first)

  second = first + 1
  Fiber.yield(second)

  second + 1
end

first_value = sequence.resume
second_value = sequence.resume
final_value = sequence.resume

puts "start=#{start}"
puts "first=#{first_value}"
puts "second=#{second_value}"
puts "final=#{final_value}"

start = 1

sequence = Fiber.new do
  first = start
  Fiber.yield(first)

  second = first + 1
  Fiber.yield(second)

  second + 1
end

first_value = sequence.resume
second_value = sequence.resume
final_value = sequence.resume

puts "start=#{start}"
puts "first=#{first_value}"
puts "second=#{second_value}"
puts "final=#{final_value}"

start = 5

sequence = Fiber.new do
  first = start
  Fiber.yield(first)

  second = first + 1
  Fiber.yield(second)

  second + 1
end

first_value = sequence.resume
second_value = sequence.resume
final_value = sequence.resume

puts "start=#{start}"
puts "first=#{first_value}"
puts "second=#{second_value}"
puts "final=#{final_value}"

  1. start ← 2, sequence ← ⟨Fiber A /tmp/execution/⟨tmp B⟩.rb:33 (created)⟩

    1start→ 2 = 2  #@start=1, 523sequence→ ⟨Fiber A /tmp/execution/⟨tmp B⟩.rb:33 (created)⟩ = Fiber.new do4  first = start5  Fiber.yield(first)67  second = first + 18  Fiber.yield(second)910  second + 111end1213first_value = sequence⟨Fiber A /tmp/execution/⟨tmp B⟩.rb:33 (created)⟩.resume14second_value = sequence.resume

  2. first ← 2

    3sequence = Fiber.new do4  first→ 2 = start25  Fiber.yield(first)

  3. sequence ← ⟨Fiber A /tmp/execution/⟨tmp B⟩.rb:33 (suspended)⟩

    4  first = start5  Fiber.yield(first)(empty)67  second = first + 18  Fiber.yield(second)910  second + 111end1213first_value→ 2 = sequence→ ⟨Fiber A /tmp/execution/⟨tmp B⟩.rb:33 (suspended)⟩.resume14second_value→ 2 = sequence⟨Fiber A /tmp/execution/⟨tmp B⟩.rb:33 (suspended)⟩.resume15final_value→ 2 = sequence⟨Fiber A /tmp/execution/⟨tmp B⟩.rb:33 (suspended)⟩.resume1617puts "start=#{start2}"18puts "first=#{first_value2}"19puts "second=#{second_value2}"20puts "final=#{final_value2}"
    outputstart=2
first=2
second=2
final=2

  1. start ← 1, sequence ← ⟨Fiber A /tmp/execution/⟨tmp B⟩.rb:33 (created)⟩

    1start→ 1 = 123sequence→ ⟨Fiber A /tmp/execution/⟨tmp B⟩.rb:33 (created)⟩ = Fiber.new do4  first = start5  Fiber.yield(first)67  second = first + 18  Fiber.yield(second)910  second + 111end1213first_value = sequence⟨Fiber A /tmp/execution/⟨tmp B⟩.rb:33 (created)⟩.resume14second_value = sequence.resume

  2. first ← 1

    3sequence = Fiber.new do4  first→ 1 = start15  Fiber.yield(first)

  3. sequence ← ⟨Fiber A /tmp/execution/⟨tmp B⟩.rb:33 (suspended)⟩

    4  first = start5  Fiber.yield(first)(empty)67  second = first + 18  Fiber.yield(second)910  second + 111end1213first_value→ 1 = sequence→ ⟨Fiber A /tmp/execution/⟨tmp B⟩.rb:33 (suspended)⟩.resume14second_value→ 1 = sequence⟨Fiber A /tmp/execution/⟨tmp B⟩.rb:33 (suspended)⟩.resume15final_value→ 1 = sequence⟨Fiber A /tmp/execution/⟨tmp B⟩.rb:33 (suspended)⟩.resume1617puts "start=#{start1}"18puts "first=#{first_value1}"19puts "second=#{second_value1}"20puts "final=#{final_value1}"
    outputstart=1
first=1
second=1
final=1

  1. start ← 5, sequence ← ⟨Fiber A /tmp/execution/⟨tmp B⟩.rb:33 (created)⟩

    1start→ 5 = 523sequence→ ⟨Fiber A /tmp/execution/⟨tmp B⟩.rb:33 (created)⟩ = Fiber.new do4  first = start5  Fiber.yield(first)67  second = first + 18  Fiber.yield(second)910  second + 111end1213first_value = sequence⟨Fiber A /tmp/execution/⟨tmp B⟩.rb:33 (created)⟩.resume14second_value = sequence.resume

  2. first ← 5

    3sequence = Fiber.new do4  first→ 5 = start55  Fiber.yield(first)

  3. sequence ← ⟨Fiber A /tmp/execution/⟨tmp B⟩.rb:33 (suspended)⟩

    4  first = start5  Fiber.yield(first)(empty)67  second = first + 18  Fiber.yield(second)910  second + 111end1213first_value→ 5 = sequence→ ⟨Fiber A /tmp/execution/⟨tmp B⟩.rb:33 (suspended)⟩.resume14second_value→ 5 = sequence⟨Fiber A /tmp/execution/⟨tmp B⟩.rb:33 (suspended)⟩.resume15final_value→ 5 = sequence⟨Fiber A /tmp/execution/⟨tmp B⟩.rb:33 (suspended)⟩.resume1617puts "start=#{start5}"18puts "first=#{first_value5}"19puts "second=#{second_value5}"20puts "final=#{final_value5}"
    outputstart=5
first=5
second=5
final=5