SERVER-43641 upgrade random.h

Respecify PseudoRandom and SecureRandom as template instances of
a `mongo::RandomBase<Urbg>` (Urbg is a UniformRandomBitGenerator).
They will only vary in which algorithm they use for their source
bits, and should otherwise support the same exact operations (e.g.
`nextCanonicalDouble`).

Fix range and stats errors in the implementations of those
RandomBase methods, and specify them in terms of the vetted
`<random>` facilities.

Test uniformity of nextInt32(max), which uses an inappropriate
( x % max) operation.  Verify that refactor fixes this issue.

Just keep a shared urandom file descriptor open.

SecureRandom add fill, remove create, fix callers

Obsoletes SERVER-43643 Re: SecureRandom 8kiB buffering

1 files changed, 6 insertions, 7 deletions

diff --git a/src/mongo/bson/oid.cpp b/src/mongo/bson/oid.cpp
index 0f08d6c56b6..ebceefa04fa 100644
--- a/src/mongo/bson/oid.cpp
+++ b/src/mongo/bson/oid.cpp
@@ -54,9 +54,9 @@ OID::InstanceUnique _instanceUnique;
 
 MONGO_INITIALIZER_GENERAL(OIDGeneration, MONGO_NO_PREREQUISITES, ("default"))
 (InitializerContext* context) {
-    std::unique_ptr<SecureRandom> entropy(SecureRandom::create());
-    counter = std::make_unique<AtomicWord<int64_t>>(entropy->nextInt64());
-    _instanceUnique = OID::InstanceUnique::generate(*entropy);
+    SecureRandom entropy;
+    counter = std::make_unique<AtomicWord<int64_t>>(entropy.nextInt64());
+    _instanceUnique = OID::InstanceUnique::generate(entropy);
     return Status::OK();
 }
 
@@ -72,9 +72,8 @@ OID::Increment OID::Increment::next() {
 }
 
 OID::InstanceUnique OID::InstanceUnique::generate(SecureRandom& entropy) {
-    int64_t rand = entropy.nextInt64();
     OID::InstanceUnique u;
-    std::memcpy(u.bytes, &rand, kInstanceUniqueSize);
+    entropy.fill(u.bytes, kInstanceUniqueSize);
     return u;
 }
 
@@ -119,8 +118,8 @@ size_t OID::Hasher::operator()(const OID& oid) const {
 }
 
 void OID::regenMachineId() {
-    std::unique_ptr<SecureRandom> entropy(SecureRandom::create());
-    _instanceUnique = InstanceUnique::generate(*entropy);
+    SecureRandom entropy;
+    _instanceUnique = InstanceUnique::generate(entropy);
 }
 
 unsigned OID::getMachineId() {