From d1bbf58619f8989f131b1496e2375e528e3f23c6 Mon Sep 17 00:00:00 2001
From: Jitendra Verma <jitendravjh@gmail.com>
Date: Sat, 3 Oct 2026 16:46:25 +0530
Subject: [PATCH] Seed a new rng instead of copying TaskLocalRNG

copy on a TaskLocalRNG snapshots the current task local state, so noise processes built back to back started from the same state and produced identical noise.
---
 src/types.jl          |  8 ++++----
 test/two_processes.jl | 15 +++++++++++++++
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/src/types.jl b/src/types.jl
index 1366d56..3baa495 100644
--- a/src/types.jl
+++ b/src/types.jl
@@ -205,7 +205,7 @@ function NoiseProcess{iip}(
         reset = true, reseed = true, continuous = true,
         cache = nothing
     ) where {iip}
-    rng = rng isa Random.TaskLocalRNG ? copy(rng) : rng
+    rng = rng isa Random.TaskLocalRNG ? Xoshiro(rand(rng, UInt64)) : rng
     S₁ = ResettableStacks.ResettableStack{iip}(
         Tuple{
             typeof(t0), typeof(W0), typeof(Z0),
@@ -417,7 +417,7 @@ mutable struct SimpleNoiseProcess{
             rng = Random.default_rng(),
             reset = true, reseed = true
         ) where {iip}
-        rng = rng isa Random.TaskLocalRNG ? copy(rng) : rng
+        rng = rng isa Random.TaskLocalRNG ? Xoshiro(rand(rng, UInt64)) : rng
         if Z0 == nothing
             Z = nothing
             curZ = nothing
@@ -915,7 +915,7 @@ mutable struct NoiseTransport{T, N, wType, zType, Tt, T2, T3, TRV, Trv, RNGType,
             reset = true, reseed = true,
             noise_prototype = W(nothing, nothing, t0, rv)
         ) where {iip}
-        rng = rng isa Random.TaskLocalRNG ? copy(rng) : rng
+        rng = rng isa Random.TaskLocalRNG ? Xoshiro(rand(rng, UInt64)) : rng
         curt = t0
         dt = t0
         curW = copy(noise_prototype)
@@ -1544,7 +1544,7 @@ function BoxWedgeTail{iip}(
         rng = Random.default_rng(),
         reset = true, reseed = true
     ) where {iip}
-    rng = rng isa Random.TaskLocalRNG ? copy(rng) : rng
+    rng = rng isa Random.TaskLocalRNG ? Xoshiro(rand(rng, UInt64)) : rng
     if Z0 === nothing
         Z = nothing
         curZ = nothing
diff --git a/test/two_processes.jl b/test/two_processes.jl
index e3f6f7c..4762f9c 100644
--- a/test/two_processes.jl
+++ b/test/two_processes.jl
@@ -33,3 +33,18 @@ Random.seed!(seed);
         @test norm(soloop.Z - sol.Z) == 0.0
     end
 end
+
+# https://github.com/SciML/DiffEqNoiseProcess.jl/issues/258
+@testset "Default rng gives each process its own stream" begin
+    W1 = WienerProcess(0.0, 0.0, 0.0; reseed = false)
+    W2 = WienerProcess(0.0, 0.0, 0.0; reseed = false)
+    sol1 = solve(NoiseProblem(W1, (0.0, 1.0)); dt = 0.1)
+    sol2 = solve(NoiseProblem(W2, (0.0, 1.0)); dt = 0.1)
+    @test sol1.W != sol2.W
+
+    W3 = WienerProcess(0.0, 0.0, 0.0; rng = Xoshiro(7), reseed = false)
+    W4 = WienerProcess(0.0, 0.0, 0.0; rng = Xoshiro(7), reseed = false)
+    sol3 = solve(NoiseProblem(W3, (0.0, 1.0)); dt = 0.1)
+    sol4 = solve(NoiseProblem(W4, (0.0, 1.0)); dt = 0.1)
+    @test sol3.W == sol4.W
+end