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https://github.com/bruno-/fiber_scheduler

Ruby's missing Fiber Scheduler implementation.
https://github.com/bruno-/fiber_scheduler

async async-programming asynchronous-programming concurrency fiber fiber-scheduler ruby

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Ruby's missing Fiber Scheduler implementation.

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README 

        
# Fiber Scheduler



Ruby 3 has

[Fiber Scheduler hooks](https://docs.ruby-lang.org/en/3.1/Fiber/SchedulerInterface.html)

that enable asynchronous programming. In order to make this work you need a

Fiber Scheduler implementation, **but Ruby does not provide a default one**.



This gem aims to fill that void by providing a Fiber Scheduler class that makes

a great default. It's easy to use, performant, and can be used with

**just built-in Ruby methods**.



`fiber_scheduler`'s killer feature 💣 is **full compatibility with any other

Fiber Scheduler implementation**, including the

[async gem](https://github.com/socketry/async). Write code using

`fiber_scheduler` and it works seamlessly with `async`, `bsync` or whatever

other `_sync` gem comes in the future.



Learn more about the Ruby's

[Fiber Scheduler feature](https://brunosutic.com/blog/ruby-fiber-scheduler).



### Installation



```

gem install fiber_scheduler

```



Requires Ruby 3.1.



### Highlights



- Enables asynchronous (colorless) programming in Ruby.

- Killer feature: full compatibility with any other Fiber Scheduler

  implementation, including the [async gem](https://github.com/socketry/async).

- Not a framework: no DSL or new APIs. Can be used with just built-in Ruby

  methods:

  [Fiber.set_scheduler](https://docs.ruby-lang.org/en/3.1/Fiber.html#method-c-set_scheduler)

  and

  [Fiber.schedule](https://docs.ruby-lang.org/en/3.1/Fiber.html#method-c-schedule).

- ~500 LOC of pure Ruby, no C extensions.

- No dependencies.



### Setup



1. With a block (recommended)

2. Set `Fiber.scheduler` directly



**With a block (recommended)**



```ruby

FiberScheduler do

  # Your code here, e.g. Fiber.schedule { ... }

end

```



Recommended because:



- This approach has

  [full compatibility with any other Fiber Scheduler](https://github.com/bruno-/fiber_scheduler#compatibility-with-other-fiber-schedulers).

- `Fiber.scheduler` is automatically un-set outside the block.



**Set Fiber.scheduler directly**



```ruby

Fiber.set_scheduler(FiberScheduler.new)



# Your code here, e.g. Fiber.schedule { ... }

```



`Fiber.scheduler` is set until the end of the current thread, unless manually

unset with `Fiber.set_scheduler(nil)`.



Pros:



- Uses only built-in Ruby methods `Fiber.set_scheduler` and `Fiber.schedule`.



Cons:



- No compatibility with other fiber schedulers.



### Examples



#### Basic example



This example runs two HTTP requests in parallel:



```ruby

require "fiber_scheduler"

require "open-uri"



FiberScheduler do

  Fiber.schedule do

    URI.open("https://httpbin.org/delay/2")

  end



  Fiber.schedule do

    URI.open("https://httpbin.org/delay/2")

  end

end

```



#### Advanced example



This example runs various operations in parallel. The example total running

time is slightly more than 2 seconds, which indicates all the operations ran in

parallel.



Note that all the operations used in `Fiber.schedule` blocks below are either

common gems or built-in Ruby methods. They all work asynchronously with this

library, no monkey patching!



```ruby

require "fiber_scheduler"

require "httparty"

require "open-uri"

require "redis"

require "sequel"



DB = Sequel.postgres

Sequel.extension(:fiber_concurrency)



FiberScheduler do

  Fiber.schedule do

    # This HTTP request takes 2 seconds (slightly more because of the latency)

    URI.open("https://httpbin.org/delay/2")

  end



  Fiber.schedule do

    # Use any HTTP library

    HTTParty.get("https://httpbin.org/delay/2")

  end



  Fiber.schedule do

    # Works with any TCP protocol library

    Redis.new.blpop("abc123", 2)

  end



  Fiber.schedule do

    # Make database queries

    DB.run("SELECT pg_sleep(2)")

  end



  Fiber.schedule do

    sleep 2

  end



  Fiber.schedule do

    # Run system commands

    `sleep 2`

  end

end

```



#### Scaling example



Easily run thousands and thousands of blocking operations in parallel. This

program finishes in about 2.5 seconds.



```ruby

require "fiber_scheduler"



FiberScheduler do

  10_000.times do

    Fiber.schedule do

      sleep 2

    end

  end

end

```



Gotcha: be careful about the overheads when scaling things. The below snippet

runs `sleep` which is an "inexpensive" operation. But, if we were to run

thousands of network requests there would be more overhead (establishing

TCP connections, SSL handshakes etc) which would prolong program running time.



#### Nested Fiber.schedule example



It's possible to nest `Fiber.schedule` blocks arbitrarily deep.



All the `sleep` operations in this snippet run in parallel and the program

finishes in 2 seconds total.



```ruby

require "fiber_scheduler"



FiberScheduler do

  Fiber.schedule do

    Fiber.schedule do

      sleep 2

    end



    Fiber.schedule do

      sleep 2

    end



    sleep 2

  end



  Fiber.schedule do

    sleep 2

  end

end

```



#### Waiting Fiber.schedule example



Sometimes it's conventient for the parent to wait on the child fiber to

complete. Use `Fiber.schedule(:waiting)` to achieve that.



In the below example fiber labeled `parent` will wait for the `child` fiber to

complete. Note that only the `parent` fiber waits, other fibers run as usual.



This example takes 4 seconds to finish.



```ruby

require "fiber_scheduler"



FiberScheduler do

  Fiber.schedule do # parent

    Fiber.schedule(:waiting) do # child

      sleep 2

    end

    # The fiber stops here until the waiting child fiber completes.



    sleep 2

  end



  Fiber.schedule do

    sleep 2

  end

end

```



#### Blocking Fiber.schedule example



Blocking fibers "block" all the other fibers from running until they're

finished.



This example takes 4 seconds to finish.



```ruby

require "fiber_scheduler"



FiberScheduler do

  Fiber.schedule do

    Fiber.schedule(:blocking) do

      sleep 2

    end

  end



  Fiber.schedule do

    sleep 2

  end

end

```



#### Volatile Fiber.schedule example



Volatile fibers end when all the "durable" fibers finish.

Volatile fibers (by design) may not complete all their work.



This is useful if you have a neverending task that performs some

cleanup work that should finish when the rest of the program completes.



This example takes 2 seconds to finish.



```ruby

require "fiber_scheduler"



FiberScheduler do

  Fiber.schedule(:volatile) do

    # This fiber will live for only 2 seconds.



    loop do

      cleanup_work # this method will run only once



      sleep 10

    end

  end



  Fiber.schedule do

    sleep 2

  end

end

```



### Compatibility with other fiber schedulers



#### [async gem](https://github.com/socketry/async)



`async` is an awesome asynchronous programming library, if not a framework.

If `async` is like Rails, then `fiber_scheduler` is plain Ruby.



`fiber_scheduler` is fully compatible with `async`:



```ruby

Async do |task|

  task.async do

    # code ...

  end



  FiberScheduler do

    Fiber.schedule do

      # code ...

    end

  end



  # ...

end

```



Note that currently the opposite doesn't work:



```ruby

FiberScheduler do

  Async do

    # ...

  end



  Fiber.schedule do # No scheduler is available! (RuntimeError)

    # ...

  end

end

```



#### Other Fiber Scheduler implementations



`fiber_scheduler` gem works with any other Fiber Scheduler class (current and

future ones). Example:



```ruby

Fiber.set_scheduler(AnotherScheduler.new)



# stuff



FiberScheduler do

  # works just fine

end



# more stuff

```



`fiber_scheduler` is like choosing pure Ruby: it's a safe choice because you

know it works and will continue working with everything else in Ruby's

asynchronous eco-system.



### Performance



This [basic perf benchmark](examples/performance.rb) looks promising.



HINT: make sure to install `io-event` gem alongside `fiber_scheduler` for a

performance improvement.



### Credits



Samuel Williams for:



- Implementing Ruby's Fiber Scheduler hooks.

- The [default selector](lib/fiber_scheduler/selector.rb) used in this gem.



### License



[MIT](LICENSE)