StableTasks.jl

StableTasks is a simple package that provides type stable tools for creating (regular and sticky) tasks. It has the following API (not exported):

• StableTasks.@spawn
• StableTasks.@spawnat
• StableTasks.@fetch
• StableTasks.@fetchfrom

StableTasks.@spawn

It works like Threads.@spawn, except it is type stable to fetch from.

julia> using StableTasks, Test

julia> @inferred fetch(StableTasks.@spawn 1 + 1)
2

versus

julia> @inferred fetch(Threads.@spawn 1 + 1)
ERROR: return type Int64 does not match inferred return type Any
Stacktrace:
 [1] error(s::String)
   @ Base ./error.jl:35
 [2] top-level scope
   @ REPL[3]:1

Note regarding the return type of @spawn:

• Threads.@spawn returns a value of the concrete type Task
• In contrast, the return type of StableTasks.@spawn may depend on any and all of the following:
  • the configuration of type inference in the Julia compiler
  • the return type of the input function
    • in particular, assuming type inference is precise, typeof(StableTasks.@spawn 3) != typeof(StableTasks.@spawn 3.0), because typeof(3) !== typeof(3.0)
• You should not write code that relies upon the exact return type of StableTasks.@spawn being concrete, or stable across versions. The return type in its parameter is available only as an optimization.

StableTasks.@spawnat

The package also provides StableTasks.@spawnat, which is similar to StableTasks.@spawn but creates a sticky task (that won't migrate) on a specific thread.

julia> t = StableTasks.@spawnat 4 Threads.threadid();

julia> @inferred fetch(t)
4

The note regarding the return type of @spawn also applies here.

StableTasks.@fetch and StableTasks.@fetchfrom

For convenience, and in analogy to at Distributed.jl, we also provide @fetch and @fetchfrom macros:

julia> StableTasks.@fetch 3+3
6

julia> StableTasks.@fetchfrom 2 Threads.threadid()
2