Seed Libc rng from system entropy (#43606)

We're seeing lots of CI failures that look like collisions in the
names of temporary variables. Currently we're seeding the libc
rng from a low entropy clock, which is somewhat likely to have
collisions particular if (as we are), you launch all your processes
at exactly the right time. Try to fix that by seeding the libc using
system entropy. Of course that still leaves the potential for birthday
problems, but hopfully this will tide us over until #43597 gets fixed.

Author: Keno

base/Base.jl

@@ -290,6 +290,9 @@ include("process.jl")
 include("ttyhascolor.jl")
 include("secretbuffer.jl")
 
+# RandomDevice support
+include("randomdevice.jl")
+
 # core math functions
 include("floatfuncs.jl")
 include("math.jl")

base/libc.jl

@@ -400,7 +400,7 @@ rand(::Type{Float64}) = rand(UInt32) * 2.0^-32
 
 Interface to the C `srand(seed)` function.
 """
-srand(seed=floor(Int, time()) % Cuint) = ccall(:srand, Cvoid, (Cuint,), seed)
+srand(seed=Base._make_uint_seed()) = ccall(:srand, Cvoid, (Cuint,), seed)
 
 struct Cpasswd
    username::Cstring

base/randomdevice.jl

@@ -0,0 +1,77 @@
+# This file is a part of Julia. License is MIT: https://julialang.org/license
+
+# This file contains the minimal support of RandomDevice for Base's own usage.
+# The actual RandomDevice type that makes use of this infrastructure is defined
+# in the Random stdlib.
+
+module DevRandomState
+    if !Sys.iswindows()
+        mutable struct FileRef
+            @atomic file::Union{IOStream, Nothing}
+        end
+        const DEV_RANDOM  = FileRef(nothing)
+        const DEV_URANDOM = FileRef(nothing)
+    end
+    function __init__()
+        if !Sys.iswindows()
+            @atomic DEV_RANDOM.file = nothing
+            @atomic DEV_URANDOM.file = nothing
+        end
+    end
+end
+
+if Sys.iswindows()
+    function RtlGenRandom!(A::Union{Array, Ref})
+        Base.windowserror("SystemFunction036 (RtlGenRandom)", 0 == ccall(
+            (:SystemFunction036, :Advapi32), stdcall, UInt8, (Ptr{Cvoid}, UInt32),
+              A, sizeof(A)))
+    end
+
+    # Manually implemented to work without the Random machinery
+    function _rand_uint()
+        r = Ref{Cuint}()
+        RtlGenRandom!(r)
+        return r[]
+    end
+else # !windows
+    function _get_dev_random_fd(unlimited::Bool)
+        ref = unlimited ? DevRandomState.DEV_URANDOM : DevRandomState.DEV_RANDOM
+        fd = ref.file
+        if fd === nothing
+            fd = open(unlimited ? "/dev/urandom" : "/dev/random")
+            old, ok = @atomicreplace ref.file nothing => fd
+            if !ok
+                close(fd)
+                fd = old::IOStream
+            end
+        end
+        return fd
+    end
+
+    # Manually implemented to work without the Random machinery
+    function _rand_uint()
+        return read(_get_dev_random_fd(true), Cuint)
+    end
+end # os-test
+
+function _ad_hoc_entropy()
+    println(stderr,
+        "Entropy pool not available to seed RNG; using ad-hoc entropy sources.")
+    seed = reinterpret(UInt64, time())
+    seed = hash(seed, getpid() % UInt)
+    try
+        seed = hash(seed, parse(UInt64,
+                                read(pipeline(`ifconfig`, `sha1sum`), String)[1:40],
+                                base = 16) % UInt)
+    catch
+    end
+    return seed
+end
+
+function _make_uint_seed()
+    try
+        _rand_uint()
+    catch
+        return _ad_hoc_entropy() % Cuint
+    end
+end

stdlib/Random/src/RNGs.jl

@@ -23,42 +23,20 @@ else # !windows
         RandomDevice(; unlimited::Bool=true) = new(unlimited)
     end
 
+    getfile(rd::RandomDevice) = Base._get_dev_random_fd(rd.unlimited)
+
     rand(rd::RandomDevice, sp::SamplerBoolBitInteger) = read(getfile(rd), sp[])
     rand(rd::RandomDevice, ::SamplerType{Bool}) = read(getfile(rd), UInt8) % Bool
 
-    mutable struct FileRef
-        @atomic file::Union{IOStream, Nothing}
-    end
-
-    const DEV_RANDOM  = FileRef(nothing)
-    const DEV_URANDOM = FileRef(nothing)
-
-    function getfile(rd::RandomDevice)
-        ref = rd.unlimited ? DEV_URANDOM : DEV_RANDOM
-        fd = ref.file
-        if fd === nothing
-            fd = open(rd.unlimited ? "/dev/urandom" : "/dev/random")
-            old, ok = @atomicreplace ref.file nothing => fd
-            if !ok
-                close(fd)
-                fd = old::IOStream
-            end
-        end
-        return fd
-    end
-
     show(io::IO, rd::RandomDevice) =
         print(io, RandomDevice, rd.unlimited ? "()" : "(unlimited=false)")
-
 end # os-test
 
 # NOTE: this can't be put within the if-else block above
 for T in (Bool, BitInteger_types...)
     if Sys.iswindows()
         @eval function rand!(rd::RandomDevice, A::Array{$T}, ::SamplerType{$T})
-            Base.windowserror("SystemFunction036 (RtlGenRandom)", 0 == ccall(
-                (:SystemFunction036, :Advapi32), stdcall, UInt8, (Ptr{Cvoid}, UInt32),
-                  A, sizeof(A)))
+            Base.RtlGenRandom!(A)
             A
         end
     else
@@ -332,14 +310,7 @@ function make_seed()
     catch
         println(stderr,
                 "Entropy pool not available to seed RNG; using ad-hoc entropy sources.")
-        seed = reinterpret(UInt64, time())
-        seed = hash(seed, getpid() % UInt)
-        try
-            seed = hash(seed, parse(UInt64,
-                                    read(pipeline(`ifconfig`, `sha1sum`), String)[1:40],
-                                    base = 16) % UInt)
-        catch
-        end
+        Base._ad_hoc_entropy_source()
         return make_seed(seed)
     end
 end
@@ -428,10 +399,6 @@ for T in BitInteger_types
 end
 
 function __init__()
-    @static if !Sys.iswindows()
-        @atomic DEV_RANDOM.file = nothing
-        @atomic DEV_URANDOM.file = nothing
-    end
     seed!(GLOBAL_RNG)
 end