Add a way to reset multiple global random seeds (#2578)

Project.toml

@@ -35,7 +35,7 @@ Polymake = "0.11.1"
 Preferences = "1"
 RandomExtensions = "0.4.3"
 RecipesBase = "1.2.1"
-Singular = "0.18.8"
+Singular = "0.18.10"
 TOPCOM_jll = "0.17.8"
 cohomCalg_jll = "0.32.0"
 julia = "1.6"

src/utils/rand.jl

@@ -1,4 +1,4 @@
-# global seed value for oscar to allow creating deterministic random number
+# global seed value for OSCAR to allow creating deterministic random number
 # generators
 # we initialize this here with a random value as well to allow use during
 # precompilation
@@ -33,3 +33,67 @@ be set to a fixed value with `Oscar.set_seed!` as it is done in `runtests.jl`.
 """
 get_seeded_rng() = return MersenneTwister([get_seed()])
 
+
+"""
+    randseed!(s::Integer)
+
+Reset the random seed for many global RNGs used by OSCAR. Currently that includes:
+- the default Julia random source, `Random.default_rng()`
+- the default FLINT random source
+- the default GAP random source `GlobalMersenneTwister`
+- the legacy GAP random source `GlobalRandomSource`
+- the Singular random sources
+
+Note that no special steps are taken for thread-local random sources (e.g. the
+default Julia random source currently is even task local). Code using multiple
+threads or multiple tasks may need to call this function from each thread or
+task.
+
+This function is *not* supposed to be called from regular code in Oscar.jl.
+Rather it is meant to help with debugging issues that depend on random
+sources. E.g. if a computation only fails sometimes, depending on randomness,
+it may be possible to make it reproducible by a trick like this:
+```julia
+  seed=0
+  while true
+    Oscar.randseed!(seed)
+    run_tricky_computation()
+    seed += 1
+  end
+```
+Once this throws an exception, we can simply record the value of `seed` at
+that time, and use that to make the error reproducible:
+```julia
+  Oscar.randseed!(1234)
+  run_tricky_computation()  # now always throws an exception
+```
+
+# Examples
+
+```jldoctest
+julia> Oscar.randseed!(1234)
+
+julia> rand(1:1000)
+219
+
+julia> GAP.Globals.Random(1,1000)
+163
+```
+"""
+randseed!(s::Integer) = randseed!(UInt32(s))
+
+function randseed!(s::UInt32)
+  # reset Julia random source on the current thread
+  Random.seed!(s)
+
+  # reset FLINT random source on the current thread
+  Nemo.randseed!(s)
+
+  # reset GAP random sources
+  GAP.randseed!(s)
+
+  # reset Singular random sources
+  Singular.randseed!(s)
+
+  return nothing
+end