Ruby - Use Thread.pass for Thread Scheduling

1. Introduction

In concurrent programming with Ruby, there may be times when it's useful to hint to the Ruby thread scheduler to pass execution to another thread. Ruby provides a method named Thread.pass that allows a thread to suggest to the scheduler to switch to the next thread. In this blog post, we will discuss how to use Thread.pass to influence thread scheduling.

Thread.pass is a method of the Thread class in Ruby. It relinquishes control from the currently executing thread to the scheduler, suggesting that the scheduler consider switching to another thread. It does not guarantee the switch but merely provides a hint. It's a way to allow other threads to run without having the current thread explicitly sleep.

2. Program Steps

1. Create two or more threads.

2. Within the threads, use Thread.pass to suggest passing execution to another thread.

3. Observe the order of execution to see how Thread.pass impacts the thread scheduling.

3. Code Program

# Step 1: Create two threads
thread1 = Thread.new do
  5.times do
    puts "Thread 1 is executing"
    # Step 2: Use Thread.pass
    Thread.pass
  end
end
thread2 = Thread.new do
  5.times do
    puts "Thread 2 is executing"
    # Step 2: Use Thread.pass
    Thread.pass
  end
end
# Ensure all threads complete their tasks before the main thread proceeds
[thread1, thread2].each(&:join)

Output:

(Thread outputs may vary because of the nature of threading)
Thread 1 is executing
Thread 2 is executing
Thread 1 is executing
Thread 2 is executing
... and so on

Explanation:

1. Thread.new do: This initiates the creation of a new thread. The subsequent block contains operations that the thread will perform.

2. puts "Thread 1 is executing": Here, we're printing a message indicating that thread 1 is currently executing.

3. Thread.pass: This is the crucial method. By calling Thread.pass, the currently executing thread gives a hint to the Ruby thread scheduler that it can switch to another thread.

4. In the output, you can observe that the order of execution for the threads may vary. However, due to the presence of Thread.pass, there's a higher likelihood of thread switching, and you might see an alternating pattern of the threads' execution.

It's essential to understand that Thread.pass does not guarantee that the scheduler will immediately pass control to another thread, but it often results in more equitable thread scheduling, especially in CPU-bound programs.