MXS-2247 Add support for random number generation to maxutils

Classes for xorshift and std random. Add a random number generator to Worker.

maxutils/maxbase/include/maxbase/random.hh

@@ -0,0 +1,154 @@
+/*
+ * Copyright (c) 2019 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl11.
+ *
+ * Change Date: 2022-01-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+#pragma once
+
+#include <maxbase/ccdefs.hh>
+
+#include <random>
+#include <array>
+
+namespace maxbase
+{
+
+/**
+ * XorShiftRandom is an extremely fast all purpose random number generator.
+ *
+ * Uses xoshiro256** http://xoshiro.di.unimi.it written in 2018 by David Blackman
+ * and Sebastiano Vigna. Comment from the source code:
+ * This is xoshiro256** 1.0, our all-purpose, rock-solid generator. It has
+ * excellent (sub-ns) speed, a state (256 bits) that is large enough for
+ * any parallel application, and it passes all tests we are aware of.
+ */
+class XorShiftRandom
+{
+public:
+    // Non-deterministic if seed == 0
+    explicit XorShiftRandom(uint64_t seed = 0);
+    uint64_t rand();
+    uint32_t rand32();
+    bool     rand_bool();
+    int64_t  b_to_e_exclusive(int64_t b, int64_t e);
+    double   zero_to_one_exclusive();
+private:
+    uint64_t rotl(const uint64_t x, int k);
+    std::array<uint64_t, 4> m_state;
+};
+
+/**
+ * StdTwisterRandom is a class for random number generation using the C++ standard library.
+ * Uses the Mersenne Twister algorithms (mt19937 and mt19937_64).
+ */
+class StdTwisterRandom
+{
+public:
+    // Non-deterministic if seed == 0
+    explicit StdTwisterRandom(uint64_t seed = 0);
+
+    uint64_t rand();
+    uint32_t rand32();
+    bool     rand_bool();
+    int64_t  b_to_e_exclusive(int64_t b, int64_t e);
+    double   zero_to_one_exclusive();
+
+    // Borrow the mt19937_64 engine for other distributions.
+    std::mt19937_64& rnd_engine();
+private:
+    std::mt19937    m_twister_engine_32;
+    std::mt19937_64 m_twister_engine_64;
+};
+
+// *********************************
+// inlined functions below this line
+
+inline uint64_t XorShiftRandom::rotl(const uint64_t x, int k)
+{
+    return (x << k) | (x >> (64 - k));
+}
+
+inline uint64_t XorShiftRandom::rand()
+{
+    // xoshiro256**
+    const uint64_t result_starstar = rotl(m_state[1] * 5, 7) * 9;
+
+    const uint64_t t = m_state[1] << 17;
+
+    m_state[2] ^= m_state[0];
+    m_state[3] ^= m_state[1];
+    m_state[1] ^= m_state[2];
+    m_state[0] ^= m_state[3];
+
+    m_state[2] ^= t;
+
+    m_state[3] = rotl(m_state[3], 45);
+
+    return result_starstar;
+}
+
+inline uint32_t XorShiftRandom::rand32()
+{
+    return rand() >> 32;    // shifting, although low bits are good
+}
+
+inline bool XorShiftRandom::rand_bool()
+{
+    return std::signbit(int64_t(rand()));
+}
+
+inline double XorShiftRandom::zero_to_one_exclusive()
+{
+    uint64_t x = rand();
+
+    // Turn uint64_t to a [0,1[ double (yes, it's standard and portable)
+    const union
+    {
+        uint64_t i;
+        double   d;
+    } u = {.i = UINT64_C(0x3FF) << 52 | x >> 12};
+
+    return u.d - 1.0;
+}
+
+inline int64_t XorShiftRandom::b_to_e_exclusive(int64_t b, int64_t e)
+{
+    // With 64 bits mod bias does not happen in practise (a very, very large e-b would be needed).
+    // alternative: return b + int64_t(zero_to_one_exclusive()*(e-b));
+    return b + rand() % (e - b);
+}
+
+inline uint64_t StdTwisterRandom::rand()
+{
+    return m_twister_engine_64();
+}
+
+inline uint32_t StdTwisterRandom::rand32()
+{
+    return m_twister_engine_32();
+}
+
+inline bool StdTwisterRandom::rand_bool()
+{
+    return std::signbit(int32_t(rand32()));
+}
+
+inline double StdTwisterRandom::zero_to_one_exclusive()
+{
+    std::uniform_real_distribution<double> zero_to_one {0, 1};
+    return zero_to_one(m_twister_engine_64);
+}
+
+inline int64_t StdTwisterRandom::b_to_e_exclusive(int64_t b, int64_t e)
+{
+    std::uniform_int_distribution<int64_t> dist {b, e - 1};
+    return dist(m_twister_engine_64);
+}
+}

maxutils/maxbase/include/maxbase/worker.hh

@@ -29,6 +29,7 @@
 #include <maxbase/semaphore.hh>
 #include <maxbase/worker.h>
 #include <maxbase/workertask.hh>
+#include <maxbase/random.hh>
 
 namespace maxbase
 {
@@ -248,11 +249,12 @@ class Worker : public MXB_WORKER
     Worker& operator=(const Worker&) = delete;
 
 public:
-    typedef WORKER_STATISTICS    STATISTICS;
-    typedef WorkerTask           Task;
-    typedef WorkerDisposableTask DisposableTask;
-    typedef WorkerLoad           Load;
-    typedef WorkerTimer          Timer;
+    using STATISTICS     = WORKER_STATISTICS;
+    using Task           = WorkerTask;
+    using DisposableTask = WorkerDisposableTask;
+    using Load           = WorkerLoad;
+    using Timer          = WorkerTimer;
+    using RandomEngine   = maxbase::XorShiftRandom;
 
     /**
      * A delegating timer that delegates the timer tick handling
@@ -369,6 +371,11 @@ public:
      */
     void get_descriptor_counts(uint32_t* pnCurrent, uint64_t* pnTotal);
 
+    /**
+     * Return the random engine of this worker.
+     */
+    RandomEngine& random_engine();
+
     /**
      * Add a file descriptor to the epoll instance of the worker.
      *
@@ -958,6 +965,7 @@ private:
     PrivateTimer*      m_pTimer;                /*< The worker's own timer. */
     DelayedCallsByTime m_sorted_calls;          /*< Current delayed calls sorted by time. */
     DelayedCallsById   m_calls;                 /*< Current delayed calls indexed by id. */
+    RandomEngine       m_random_engine;         /*< Random engine for this worker (this thread). */
 
     int32_t m_next_delayed_call_id;     /*< The next delayed call id. */
 };

maxutils/maxbase/src/CMakeLists.txt

@@ -15,6 +15,7 @@ add_library(maxbase STATIC
   worker.cc
   workertask.cc
   average.cc
+  random.cc
   )
 
 if(HAVE_SYSTEMD)

maxutils/maxbase/src/random.cc

@@ -0,0 +1,53 @@
+/*
+ * Copyright (c) 2019 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl11.
+ *
+ * Change Date: 2022-01-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+
+#include <maxbase/random.hh>
+
+namespace maxbase
+{
+
+static uint64_t splitmix(uint64_t& state)
+{
+    uint64_t z = (state += 0x9e3779b97f4a7c15);
+    z = (z ^ (z >> 30)) * 0xbf58476d1ce4e5b9;
+    z = (z ^ (z >> 27)) * 0x94d049bb133111eb;
+    return z ^ (z >> 31);
+}
+
+XorShiftRandom::XorShiftRandom(uint64_t seed)
+{
+    if (!seed)
+    {
+        std::random_device rdev;
+        while (!(seed = rdev()))
+        {
+        }
+    }
+    for (auto& s : m_state)
+    {
+        s = splitmix(seed);
+    }
+}
+
+StdTwisterRandom::StdTwisterRandom(uint64_t seed)
+{
+    std::random_device rdev;
+    m_twister_engine_32.seed(seed ? seed : rdev());
+    m_twister_engine_64.seed(seed ? seed : rdev());
+}
+
+std::mt19937_64& StdTwisterRandom::rnd_engine()
+{
+    return m_twister_engine_64;
+}
+}

maxutils/maxbase/src/worker.cc

@@ -355,6 +355,11 @@ void Worker::get_descriptor_counts(uint32_t* pnCurrent, uint64_t* pnTotal)
     *pnTotal = atomic_load_uint64(&m_nTotal_descriptors);
 }
 
+Worker::RandomEngine& Worker::random_engine()
+{
+    return m_random_engine;
+}
+
 bool Worker::add_fd(int fd, uint32_t events, MXB_POLL_DATA* pData)
 {
     bool rv = true;

server/modules/routing/readwritesplit/rwsplit_select_backends.cc

@@ -28,15 +28,6 @@
 
 using namespace maxscale;
 
-// TODO, there should be a utility with the most common used random cases.
-// FYI: rand() is about twice as fast as the below toss.
-static std::mt19937 random_engine;
-static std::uniform_real_distribution<> zero_to_one(0.0, 1.0);
-double toss()
-{
-    return zero_to_one(random_engine);
-}
-
 /**
  * The functions that implement back end selection for the read write
  * split router. All of these functions are internal to that router and
@@ -161,7 +152,8 @@ PRWBackends::iterator backend_cmp_response_time(PRWBackends& sBackends)
     }
 
     // Find the winner, role the ball:
-    double ball = toss();
+    double ball = maxbase::Worker::get_current()->random_engine().zero_to_one_exclusive();
+
     double slot_walk {0};
     int winner {0};