Ruby Fibers provide a powerful mechanism for implementing lightweight, cooperative concurrency in Ruby programs. They offer a way to create small, independent units of execution that can be paused and resumed at will.

What are Fibers?

Fibers are primitives for implementing light-weight cooperative concurrency in Ruby. Unlike Ruby Threads, which are preemptively scheduled by the operating system, Fibers are cooperatively scheduled by the programmer. This allows for fine-grained control over execution flow.

Creating and Using Fibers

To create a Fiber, use the Fiber.new constructor with a block. The Fiber's execution begins when you call resume on it. Here's a simple example:


fiber = Fiber.new do
  puts "Inside the fiber"
  Fiber.yield "Hello from fiber!"
  puts "Fiber resumed"
end

puts fiber.resume
puts "Back in the main program"
puts fiber.resume

This code demonstrates the basic lifecycle of a Fiber: creation, initial resumption, yielding, and final resumption.

Fiber Methods

Fiber.yield: Suspends the fiber's execution and returns control to the caller.
fiber.resume: Resumes the execution of the fiber from where it last yielded.
Fiber.current: Returns the currently executing fiber.

Use Cases for Fibers

Fibers are particularly useful in scenarios where you need fine-grained control over execution flow. Some common use cases include:

Implementing generators or iterators
Cooperative multitasking in event-driven programming
Managing complex control flow in game development
Implementing coroutines for asynchronous programming

Implementing a Simple Generator with Fibers

Here's an example of using a Fiber to create a simple generator that yields Fibonacci numbers:


fib = Fiber.new do
  a, b = 0, 1
  loop do
    Fiber.yield a
    a, b = b, a + b
  end
end

10.times { puts fib.resume }

This Fiber generates Fibonacci numbers indefinitely, yielding each number in the sequence when resumed.

Considerations and Best Practices

Fibers are not thread-safe. Be cautious when using them in multithreaded environments.
Fibers are subject to the Ruby GIL (Global Interpreter Lock), so they don't provide true parallelism.
Use Fibers for cooperative multitasking scenarios where you need fine-grained control over execution flow.
Consider using Fibers in combination with event loops for efficient asynchronous programming.

Conclusion

Ruby Fibers offer a powerful tool for implementing lightweight concurrency and managing complex control flows. By understanding their creation, resumption, and yielding mechanisms, you can leverage Fibers to write more efficient and elegant Ruby code for scenarios requiring fine-grained execution control.