Process forking for parallelism in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a child process using fork.

Ruby

pid = [1]

Drag options to blanks, or click blank then click option'

Afork

Bspawn

Cfork()

Dexec

Attempts:

3 left

💡 Hint

Common Mistakes

Using spawn instead of fork.

Adding parentheses after fork.

In Ruby, fork creates a child process and returns its process ID.

2fill in blank

medium

Complete the code to check if the current process is the child process.

Ruby

if pid == [1]
  puts "Child process"
end

Drag options to blanks, or click blank then click option'

Anil

B0

C-1

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for nil instead of 0.

Using 1 or -1 as the child process ID.

In Ruby, fork returns 0 in the child process.

3fill in blank

hard

Fix the error in the code to wait for the child process to finish.

Ruby

Process.[1](pid)

Drag options to blanks, or click blank then click option'

Awaitpid

Bwait

Cwaitall

Dwaitchild

Attempts:

3 left

💡 Hint

Common Mistakes

Using Process.wait which waits for any child process.

Using non-existent methods like waitchild.

The correct method to wait for a specific child process is Process.waitpid.

4fill in blank

hard

Fill both blanks to create two child processes and print their PIDs.

Ruby

2.times do
  pid = [1]
  if pid == [2]
    puts "Child PID: #{Process.pid}"
    exit
  end
end

Drag options to blanks, or click blank then click option'

Afork

B0

C1

Dspawn

Attempts:

3 left

💡 Hint

Common Mistakes

Using spawn instead of fork.

Checking if pid == 1 instead of 0.

Use fork to create child processes and check if pid == 0 to identify the child.

5fill in blank

hard

Fill all three blanks to collect child PIDs and wait for them to finish.

Ruby

pids = []
3.times do
  pids << [1]
end

pids.each do |pid|
  Process.[2](pid)
  puts "Child process [3] finished"
end

Drag options to blanks, or click blank then click option'

Afork

Bwaitpid

CPID

Dwait

Attempts:

3 left

💡 Hint

Common Mistakes

Using wait instead of waitpid for specific PIDs.

Using incorrect words in the message.

Use fork to create child processes, waitpid to wait for each, and print a message when done.

Practice

1. What does the fork method do in Ruby?

easy

A. It pauses the current process until a condition is met.

B. It creates a new child process that runs concurrently with the parent.

C. It merges two processes into one.

D. It terminates the current process immediately.

Solution

1. Step 1: Understand the purpose of fork

   The fork method creates a new process, called the child, which runs alongside the original parent process.

2. Step 2: Identify the behavior of the child process

   The child process runs the code block given to fork independently, allowing parallel execution.

3. Final Answer:

   It creates a new child process that runs concurrently with the parent. -> Option B

4. Quick Check:

   fork creates child process = A [OK]

Hint: Fork means start a new process running alongside parent [OK]

Common Mistakes:

• Thinking fork pauses the process
• Confusing fork with process termination
• Assuming fork merges processes

2. Which of the following is the correct syntax to create a child process using fork in Ruby?

easy

A. child_pid = fork puts 'Hello from child'

B. fork = child_pid { puts 'Hello from child' }

C. fork child_pid { puts 'Hello from child' }

D. child_pid = fork { puts 'Hello from child' }

Solution

1. Step 1: Recall the correct fork syntax

   The fork method takes a block with curly braces or do-end to run code in the child process.

2. Step 2: Check each option's syntax

   child_pid = fork { puts 'Hello from child' } correctly assigns the child process ID and uses a block with curly braces. Options A, C, and D have syntax errors or incorrect usage.

3. Final Answer:

   child_pid = fork { puts 'Hello from child' } -> Option D

4. Quick Check:

   Use block with fork = B [OK]

Hint: Fork needs a block with braces or do-end [OK]

Common Mistakes:

• Omitting braces for the block
• Assigning fork incorrectly
• Using wrong order of arguments

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

pid = fork do
  puts 'Child process'
end
Process.wait(pid)
puts 'Parent process'

medium

A. Child process
Parent process

B. Child process

C. Parent process
Child process

D. Parent process

Solution

1. Step 1: Understand the fork and wait behavior

   The fork creates a child process that prints 'Child process'. The parent waits for the child to finish using Process.wait(pid).

2. Step 2: Determine output order

   The child prints first, then the parent prints 'Parent process' after the child ends.

3. Final Answer:

   Child process Parent process -> Option A

4. Quick Check:

   Child prints before parent after wait = C [OK]

Hint: Parent waits, so child prints first [OK]

Common Mistakes:

• Assuming parent prints first
• Ignoring Process.wait effect
• Confusing output order

4. Identify the error in this Ruby code using fork:

pid = fork do
  puts 'Child running'
end
puts 'Parent running'
Process.wait

medium

A. Process.wait called without PID argument

B. Missing block for fork

C. fork does not return a PID

D. puts statements are inside the fork block

Solution

1. Step 1: Check usage of Process.wait

   The Process.wait method should be called with the child's PID to wait for that specific process.

2. Step 2: Identify the error

   In the code, Process.wait is called without any argument, which waits for any child process but can cause unexpected behavior or errors if multiple children exist.

3. Final Answer:

   Process.wait called without PID argument -> Option A

4. Quick Check:

   Always pass PID to Process.wait = A [OK]

Hint: Pass child PID to Process.wait to avoid errors [OK]

Common Mistakes:

• Calling Process.wait without PID
• Confusing fork return value
• Misplacing puts statements

5. You want to run two tasks in parallel using fork and wait for both to finish before continuing. Which code correctly achieves this?

hard

A. pids = fork { task1; task2 }
Process.wait(pids)
puts 'Both done'

B. fork { task1 }
fork { task2 }
puts 'Both done'

C. pids = []
pids << fork { task1 }
pids << fork { task2 }
pids.each { |pid| Process.wait(pid) }
puts 'Both done'

D. fork { task1; Process.wait }
fork { task2; Process.wait }
puts 'Both done'

Solution

1. Step 1: Understand how to fork multiple processes

   Each fork creates a child process. To run two tasks in parallel, fork twice and store both child PIDs.

2. Step 2: Wait for both child processes

   Use Process.wait(pid) for each PID to ensure both finish before continuing.

3. Step 3: Analyze options

   pids = [] pids << fork { task1 } pids << fork { task2 } pids.each { |pid| Process.wait(pid) } puts 'Both done' correctly forks twice, stores PIDs, waits for both, then prints. Others either don't wait or misuse fork.

4. Final Answer:

   pids = [] pids << fork { task1 } pids << fork { task2 } pids.each { |pid| Process.wait(pid) } puts 'Both done' -> Option C

5. Quick Check:

   Fork twice, wait both PIDs = D [OK]

Hint: Store PIDs, wait each to sync parallel tasks [OK]

Common Mistakes:

• Not waiting for child processes
• Calling Process.wait inside child
• Forking once for multiple tasks