add experimental @spawn macro to Base.Threads (#32600)

Author: JeffBezanson

NEWS.md

@@ -19,6 +19,7 @@ Multi-threading changes
   although it specifically does include `BufferStream`.
   ([#32309], [#32174], [#31981], [#32421]).
 * The global random number generator (`GLOBAL_RNG`) is now thread-safe (and thread-local) ([#32407]).
+* New experimental `Threads.@spawn` macro that runs a task on any available thread ([#32600]).
 
 Build system changes
 --------------------
@@ -104,3 +105,29 @@ Tooling Improvements
   may be run using `make -C src analyzegc`.
 
 <!--- generated by NEWS-update.jl: -->
+[#23422]: https://github.com/JuliaLang/julia/issues/23422
+[#24353]: https://github.com/JuliaLang/julia/issues/24353
+[#31066]: https://github.com/JuliaLang/julia/issues/31066
+[#31459]: https://github.com/JuliaLang/julia/issues/31459
+[#31576]: https://github.com/JuliaLang/julia/issues/31576
+[#31654]: https://github.com/JuliaLang/julia/issues/31654
+[#31664]: https://github.com/JuliaLang/julia/issues/31664
+[#31781]: https://github.com/JuliaLang/julia/issues/31781
+[#31834]: https://github.com/JuliaLang/julia/issues/31834
+[#31838]: https://github.com/JuliaLang/julia/issues/31838
+[#31853]: https://github.com/JuliaLang/julia/issues/31853
+[#31916]: https://github.com/JuliaLang/julia/issues/31916
+[#31981]: https://github.com/JuliaLang/julia/issues/31981
+[#32002]: https://github.com/JuliaLang/julia/issues/32002
+[#32103]: https://github.com/JuliaLang/julia/issues/32103
+[#32122]: https://github.com/JuliaLang/julia/issues/32122
+[#32133]: https://github.com/JuliaLang/julia/issues/32133
+[#32174]: https://github.com/JuliaLang/julia/issues/32174
+[#32260]: https://github.com/JuliaLang/julia/issues/32260
+[#32300]: https://github.com/JuliaLang/julia/issues/32300
+[#32308]: https://github.com/JuliaLang/julia/issues/32308
+[#32309]: https://github.com/JuliaLang/julia/issues/32309
+[#32407]: https://github.com/JuliaLang/julia/issues/32407
+[#32421]: https://github.com/JuliaLang/julia/issues/32421
+[#32534]: https://github.com/JuliaLang/julia/issues/32534
+[#32600]: https://github.com/JuliaLang/julia/issues/32600

base/threadingconstructs.jl

@@ -102,3 +102,30 @@ macro threads(args...)
         throw(ArgumentError("unrecognized argument to @threads"))
     end
 end
+
+"""
+    Threads.@spawn expr
+
+Create and run a [`Task`](@ref) on any available thread. To wait for the task to
+finish, call [`wait`](@ref) on the result of this macro, or call [`fetch`](@ref)
+to wait and then obtain its return value.
+
+!!! note
+    This feature is currently considered experimental.
+
+!!! compat "Julia 1.3"
+    This macro is available as of Julia 1.3.
+"""
+macro spawn(expr)
+    thunk = esc(:(()->($expr)))
+    var = esc(Base.sync_varname)
+    quote
+        local task = Task($thunk)
+        task.sticky = false
+        if $(Expr(:isdefined, var))
+            push!($var, task)
+        end
+        schedule(task)
+        task
+    end
+end

doc/src/base/multi-threading.md

@@ -7,6 +7,7 @@ described here might (and likely will) change in the future.
 Base.Threads.threadid
 Base.Threads.nthreads
 Base.Threads.@threads
+Base.Threads.@spawn
 ```
 
 ```@docs

test/threads_exec.jl

@@ -647,9 +647,7 @@ function pfib(n::Int)
     if n <= 1
         return n
     end
-    t = @task pfib(n-2)
-    t.sticky = false
-    schedule(t)
+    t = Threads.@spawn pfib(n-2)
     return pfib(n-1) + fetch(t)::Int
 end
 @test pfib(20) == 6765