Merge pull request #134 from GianlucaFuwa/master

Fix `threadlocal` type-inferrability and add `reduction` functionality

Author: chriselrod

README.md

@@ -197,8 +197,6 @@ BenchmarkTools.Trial: 10000 samples with 10 evaluations.
 
 ### Local per-thread storage (`threadlocal`)
 
-**Warning: this feature is likely broken!**
-
 You also can define local storage for each thread, providing a vector containing each of the local storages at the end.
 
 ```julia
@@ -234,6 +232,25 @@ julia> let
 Float16[83.0, 90.0, 27.0, 65.0]
 ```
 
+### `reduction`
+The `reduction` keyword enables reduction of an already initialized `isbits` variable with certain supported associative operations (see [docs](https://JuliaSIMD.github.io/Polyester.jl/stable)), such that the transition from serialized code is as simple as adding the `@batch` macro. Contrary to `threadlocal` this does not incur any additional allocations
+
+```julia
+julia> function batch_reduction()
+           y1 = 0
+           y2 = 1
+           @batch reduction=((+, y1), (*, y2)) for i in 1:9
+               y1 += i
+               y2 *= i
+           end
+           y1, y2
+       end
+julia> batch_reduction()
+(45, 362880)
+julia> @allocated batch_reduction()
+0
+```
+
 ## Disabling Polyester threads
 
 When running many repetitions of a Polyester-multithreaded function (e.g. in an embarrassingly parallel problem that repeatedly executes a small already Polyester-multithreaded function), it can be beneficial to disable Polyester (the inner multithreaded loop) and multithread only at the outer level (e.g. with `Base.Threads`). This can be done with the `disable_polyester_threads` context manager. In the expandable section below you can see examples with benchmarks.

src/Polyester.jl

@@ -6,6 +6,7 @@ end
 using ThreadingUtilities
 import StaticArrayInterface
 const ArrayInterface = StaticArrayInterface
+using Base.Cartesian: @nexprs
 using StaticArrayInterface: static_length, static_step, static_first, static_size
 using StrideArraysCore: object_and_preserve
 using ManualMemory: Reference
@@ -23,6 +24,15 @@ using CPUSummary: num_cores
 
 export batch, @batch, disable_polyester_threads
 
+const SUPPORTED_REDUCE_OPS = (:+, :*, :min, :max, :&, :|)
+initializer(::typeof(+), ::T) where {T} = zero(T)
+initializer(::typeof(+), ::Bool) = zero(Int)
+initializer(::typeof(*), ::T) where {T} = one(T)
+initializer(::typeof(min), ::T) where {T} = typemax(T)
+initializer(::typeof(max), ::T) where {T} = typemin(T)
+initializer(::typeof(&), ::Bool) = true
+initializer(::typeof(|), ::Bool) = false
+
 include("batch.jl")
 include("closure.jl")
 
@@ -38,10 +48,4 @@ function reset_threads!()
   foreach(ThreadingUtilities.checktask, eachindex(ThreadingUtilities.TASKS))
   return nothing
 end
-
-# y = rand(1)
-# x = rand(1)
-# @batch for i ∈ eachindex(y,x)
-#   y[i] = sin(x[i])
-# end
 end