From 9a39a125b236a1aa3c6abd3c3799105756ac084f Mon Sep 17 00:00:00 2001
From: Mislav Bradac <mislav.bradac@memgraph.io>
Date: Tue, 29 Aug 2017 10:23:22 +0200
Subject: [PATCH] Remove rand from dba

Reviewers: florijan, buda

Reviewed By: florijan

Subscribers: pullbot

Differential Revision: https://phabricator.memgraph.io/D721
---
 src/database/graph_db_accessor.cpp                 |  6 +-----
 src/database/graph_db_accessor.hpp                 |  9 ---------
 src/query/interpret/awesome_memgraph_functions.cpp |  7 +++++--
 tests/unit/graph_db_accessor.cpp                   | 13 -------------
 4 files changed, 6 insertions(+), 29 deletions(-)

diff --git a/src/database/graph_db_accessor.cpp b/src/database/graph_db_accessor.cpp
index cecee848f..d8465c57a 100644
--- a/src/database/graph_db_accessor.cpp
+++ b/src/database/graph_db_accessor.cpp
@@ -9,9 +9,7 @@
 #include "utils/on_scope_exit.hpp"
 
 GraphDbAccessor::GraphDbAccessor(GraphDb &db)
-    : db_(db), transaction_(db.tx_engine_.Begin()) {
-  pseudo_rand_gen_.seed(std::random_device()());
-}
+    : db_(db), transaction_(db.tx_engine_.Begin()) {}
 
 GraphDbAccessor::~GraphDbAccessor() {
   if (!commited_ && !aborted_) {
@@ -334,5 +332,3 @@ const std::string &GraphDbAccessor::PropertyName(
   debug_assert(!commited_ && !aborted_, "Accessor committed or aborted");
   return *property;
 }
-
-double GraphDbAccessor::Rand() { return rand_dist_(pseudo_rand_gen_); }
diff --git a/src/database/graph_db_accessor.hpp b/src/database/graph_db_accessor.hpp
index 47bd958b2..993f7a312 100644
--- a/src/database/graph_db_accessor.hpp
+++ b/src/database/graph_db_accessor.hpp
@@ -553,11 +553,6 @@ class GraphDbAccessor {
     if (!accessor.new_) accessor.new_ = accessor.vlist_->update(*transaction_);
   }
 
-  /**
-   * Returns a uniformly random-generated number from the [0, 1) interval.
-   */
-  double Rand();
-
  private:
   /**
    * Insert this vertex into corresponding label and label+property (if it
@@ -598,8 +593,4 @@ class GraphDbAccessor {
 
   bool commited_{false};
   bool aborted_{false};
-
-  // Random number generation stuff.
-  std::mt19937 pseudo_rand_gen_;
-  std::uniform_real_distribution<> rand_dist_{0, 1};
 };
diff --git a/src/query/interpret/awesome_memgraph_functions.cpp b/src/query/interpret/awesome_memgraph_functions.cpp
index 304c5e499..c7acca997 100644
--- a/src/query/interpret/awesome_memgraph_functions.cpp
+++ b/src/query/interpret/awesome_memgraph_functions.cpp
@@ -4,6 +4,7 @@
 #include <cmath>
 #include <cstdlib>
 #include <functional>
+#include <random>
 
 #include "query/exceptions.hpp"
 #include "utils/string.hpp"
@@ -453,11 +454,13 @@ TypedValue Pi(const std::vector<TypedValue> &args, GraphDbAccessor &) {
   return M_PI;
 }
 
-TypedValue Rand(const std::vector<TypedValue> &args, GraphDbAccessor &dba) {
+TypedValue Rand(const std::vector<TypedValue> &args, GraphDbAccessor &) {
+  static thread_local std::mt19937 pseudo_rand_gen_{std::random_device{}()};
+  static thread_local std::uniform_real_distribution<> rand_dist_{0, 1};
   if (args.size() != 0U) {
     throw QueryRuntimeException("rand shouldn't be called with arguments");
   }
-  return dba.Rand();
+  return rand_dist_(pseudo_rand_gen_);
 }
 
 template <bool (*Predicate)(const std::string &s1, const std::string &s2)>
diff --git a/tests/unit/graph_db_accessor.cpp b/tests/unit/graph_db_accessor.cpp
index 083528e3c..b99084761 100644
--- a/tests/unit/graph_db_accessor.cpp
+++ b/tests/unit/graph_db_accessor.cpp
@@ -352,19 +352,6 @@ TEST(GraphDbAccessorTest, Transfer) {
   EXPECT_EQ(dba3->Transfer(e12)->PropsAt(prop).Value<int64_t>(), 12);
 }
 
-TEST(GraphDbAccessorTest, Rand) {
-  Dbms dbms;
-  auto dba = dbms.active();
-
-  double a = dba->Rand();
-  EXPECT_GE(a, 0.0);
-  EXPECT_LT(a, 1.0);
-  double b = dba->Rand();
-  EXPECT_GE(b, 0.0);
-  EXPECT_LT(b, 1.0);
-  EXPECT_NE(a, b);
-}
-
 int main(int argc, char **argv) {
   ::testing::InitGoogleTest(&argc, argv);
   //  ::testing::GTEST_FLAG(filter) = "*.DetachRemoveVertex";