remove incorrect examples about thread-unsafe functions in docs (Juli…

…aLang#33419)

* remove incorrect examples about thread unsafe functions

* Delete my_file.txt

doc/src/manual/parallel-computing.md

@@ -396,95 +396,7 @@ When using multi-threading we have to be careful when using functions that are n
 For instance functions that have their
 [name ending with `!`](https://docs.julialang.org/en/latest/manual/style-guide/#Append-!-to-names-of-functions-that-modify-their-arguments-1)
 by convention modify their arguments and thus are not pure. However, there are
-functions that have side effects and their name does not end with `!`. For
-instance [`findfirst(regex, str)`](@ref) mutates its `regex` argument or
-[`rand()`](@ref) changes `Base.GLOBAL_RNG` :
-
-```julia-repl
-julia> using Base.Threads
-
-julia> nthreads()
-4
-
-julia> function f()
- s = repeat(["123", "213", "231"], outer=1000)
- x = similar(s, Int)
- rx = r"1"
- @threads for i in 1:3000
- x[i] = findfirst(rx, s[i]).start
- end
- count(v -> v == 1, x)
- end
-f (generic function with 1 method)
-
-julia> f() # the correct result is 1000
-1017
-
-julia> function g()
- a = zeros(1000)
- @threads for i in 1:1000
- a[i] = rand()
- end
- length(unique(a))
- end
-g (generic function with 1 method)
-
-julia> Random.seed!(1); g() # the result for a single thread is 1000
-781
-```
-
-In such cases one should redesign the code to avoid the possibility of a race condition or use
-[synchronization primitives](https://docs.julialang.org/en/latest/base/multi-threading/#Synchronization-Primitives-1).
-
-For example in order to fix `findfirst` example above one needs to have a
-separate copy of `rx` variable for each thread:
-
-```julia-repl
-julia> function f_fix()
- s = repeat(["123", "213", "231"], outer=1000)
- x = similar(s, Int)
- rx = [Regex("1") for i in 1:nthreads()]
- @threads for i in 1:3000
- x[i] = findfirst(rx[threadid()], s[i]).start
- end
- count(v -> v == 1, x)
- end
-f_fix (generic function with 1 method)
-
-julia> f_fix()
-1000
-```
-
-We now use `Regex("1")` instead of `r"1"` to make sure that Julia
-creates separate instances of `Regex` object for each entry of `rx` vector.
-
-The case of `rand` is a bit more complex as we have to ensure that each thread
-uses non-overlapping pseudorandom number sequences. This can be simply ensured
-by using `Future.randjump` function:
-
-
-```julia-repl
-julia> using Random; import Future
-
-julia> function g_fix(r)
- a = zeros(1000)
- @threads for i in 1:1000
- a[i] = rand(r[threadid()])
- end
- length(unique(a))
- end
-g_fix (generic function with 1 method)
-
-julia> r = let m = MersenneTwister(1)
- [m; accumulate(Future.randjump, fill(big(10)^20, nthreads()-1), init=m)]
- end;
-
-julia> g_fix(r)
-1000
-```
-
-We pass the `r` vector to `g_fix` as generating several RGNs is an expensive
-operation so we do not want to repeat it every time we run the function.
+functions that have side effects and their name does not end with `!`.
 
 ## @threadcall (Experimental)