make pmap default to using a CachingPool

Update stdlib/Distributed/src/pmap.jl
Update NEWS.md
use some workers

Author: oxinabox

NEWS.md

@@ -34,6 +34,8 @@ New library features
 Standard library changes
 ------------------------
 
+* `pmap` now defaults to using a `CachingPool` ([#33892]).
+
 #### Package Manager
 
 #### LinearAlgebra

stdlib/Distributed/src/pmap.jl

@@ -40,8 +40,8 @@ For multiple collection arguments, apply `f` elementwise.
 Note that `f` must be made available to all worker processes; see
 [Code Availability and Loading Packages](@ref code-availability) for details.
 
-If a worker pool is not specified, all available workers, i.e., the default worker pool
-is used.
+If a worker pool is not specified all available workers will be used via a [`CachingPool`](@ref).
+
 
 By default, `pmap` distributes the computation over all specified workers. To use only the
 local process and distribute over tasks, specify `distributed=false`.
@@ -153,7 +153,7 @@ function pmap(f, p::AbstractWorkerPool, c; distributed=true, batch_size=1, on_er
 end
 
 pmap(f, p::AbstractWorkerPool, c1, c...; kwargs...) = pmap(a->f(a...), p, zip(c1, c...); kwargs...)
-pmap(f, c; kwargs...) = pmap(f, default_worker_pool(), c; kwargs...)
+pmap(f, c; kwargs...) = pmap(f, CachingPool(workers()), c; kwargs...)
 pmap(f, c1, c...; kwargs...) = pmap(a->f(a...), zip(c1, c...); kwargs...)
 
 function wrap_on_error(f, on_error; capture_data=false)