ResumableFunctions

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C# has a convenient way to create iterators using the yield return statement. The package ResumableFunctions provides the same functionality for the Julia language by introducing the @resumable and the @yield macros. These macros can be used to replace the Task switching functions produce and consume which were deprecated in Julia v0.6. Channels are the preferred way for inter-task communication in julia v0.6+, but their performance is subpar for iterator applications. See the benchmarks section below.

ResumableFunctions is a registered package and can be installed by running:

using Pkg
Pkg.add("ResumableFunctions")

using ResumableFunctions

@resumable function fibonacci(n::Int) :: Int
  a = 0
  b = 1
  for i in 1:n
    @yield a
    a, b = b, a+b
  end
end

for fib in fibonacci(10)
  println(fib)
end

# Example with specifies the length
using ResumableFunctions

@resumable length=n^2 function fibonacci(n::Int) :: Int
  a = 0
  b = 1
  for i in 1:n^2
    @yield a
    a, b = b, a+b
  end
end

for fib in fibonacci(5)
  println(fib)
end

The following block is the result of running julia --project=. benchmark/benchmarks.jl on a Macbook Pro with following processor: Intel Core i9 2.4 GHz 8-Core. Julia version 1.5.3 was used.

Fibonacci with Int values:

Direct: 
  27.184 ns (0 allocations: 0 bytes)
ResumableFunctions: 
  27.503 ns (0 allocations: 0 bytes)
Channels csize=0: 
  2.438 ms (101 allocations: 3.08 KiB)
Channels csize=1: 
  2.546 ms (23 allocations: 1.88 KiB)
Channels csize=20: 
  138.681 μs (26 allocations: 2.36 KiB)
Channels csize=100: 
  35.071 μs (28 allocations: 3.95 KiB)
Task scheduling
  17.726 μs (86 allocations: 3.31 KiB)
Closure: 
  1.948 μs (82 allocations: 1.28 KiB)
Closure optimised: 
  25.910 ns (0 allocations: 0 bytes)
Closure statemachine: 
  28.048 ns (0 allocations: 0 bytes)
Iteration protocol: 
  41.143 ns (0 allocations: 0 bytes)

Fibonacci with BigInt values:

Direct: 
  5.747 μs (188 allocations: 4.39 KiB)
ResumableFunctions: 
  5.984 μs (191 allocations: 4.50 KiB)
Channels csize=0: 
  2.508 ms (306 allocations: 7.75 KiB)
Channels csize=1: 
  2.629 ms (306 allocations: 7.77 KiB)
Channels csize=20: 
  150.274 μs (309 allocations: 8.25 KiB)
Channels csize=100: 
  44.592 μs (311 allocations: 9.84 KiB)
Task scheduling
  24.802 μs (198 allocations: 6.61 KiB)
Closure: 
  7.064 μs (192 allocations: 4.47 KiB)
Closure optimised: 
  5.809 μs (190 allocations: 4.44 KiB)
Closure statemachine: 
  5.826 μs (190 allocations: 4.44 KiB)
Iteration protocol: 
  5.822 μs (190 allocations: 4.44 KiB)

• Ben Lauwens, Royal Military Academy, Brussels, Belgium.
• JuliaDynamics and QuantumSavory volunteers.

• To discuss problems or feature requests, file an issue. For bugs, please include as much information as possible, including operating system, julia version, and version of MacroTools.
• To contribute, make a pull request. Contributions should include tests for any new features/bug fixes.

A detailed change log is kept.

• In a try block only top level @yield statements are allowed.
• In a finally block a @yield statement is not allowed.
• An anonymous function can not contain a @yield statement.
• Many more restrictions.