From a0975b40624dc2fe7bd57354490c397cf0e2b3b7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Manuel=20P=C3=B6ter?= <manuel@manuel-poeter.at>
Date: Thu, 14 Feb 2019 15:35:42 +0100
Subject: [PATCH] Switch to thread-local RandomDevice instances. (#8150)

---
 lib/Basics/operating-system.h  |  6 -----
 lib/Random/RandomGenerator.cpp | 41 ++++++++++++++--------------------
 lib/Random/RandomGenerator.h   |  6 +++--
 3 files changed, 21 insertions(+), 32 deletions(-)

diff --git a/lib/Basics/operating-system.h b/lib/Basics/operating-system.h
index 2308b8830a..6dbf4f4476 100644
--- a/lib/Basics/operating-system.h
+++ b/lib/Basics/operating-system.h
@@ -290,10 +290,6 @@
 
 #define TRI_SC_NPROCESSORS_ONLN 1
 
-#if __llvm__ == 1
-#define thread_local __thread
-#endif
-
 // alignment and limits
 
 #if __WORDSIZE == 64
@@ -789,8 +785,6 @@ typedef unsigned char bool;
 
 #define alloca _alloca
 
-#define thread_local __declspec(thread)
-
 // alignment and limits
 
 #if __WORDSIZE == 64
diff --git a/lib/Random/RandomGenerator.cpp b/lib/Random/RandomGenerator.cpp
index 9d3ffd8f5b..ca3d7b649a 100644
--- a/lib/Random/RandomGenerator.cpp
+++ b/lib/Random/RandomGenerator.cpp
@@ -440,13 +440,19 @@ class RandomDeviceWin32 : public RandomDevice {
 // RandomGenerator
 // -----------------------------------------------------------------------------
 
-Mutex RandomGenerator::_lock;
-std::unique_ptr<RandomDevice> RandomGenerator::_device(nullptr);
+RandomGenerator::RandomType RandomGenerator::_type;
+thread_local std::unique_ptr<RandomDevice> RandomGenerator::_device(nullptr);
 
 void RandomGenerator::initialize(RandomType type) {
-  MUTEX_LOCKER(guard, _lock);
+  _type = type;
+}
 
-  switch (type) {
+void RandomGenerator::ensureDeviceIsInitialized() {
+  if (_device) {
+    return;
+  }
+
+  switch (_type) {
     case RandomType::MERSENNE: {
       _device.reset(new RandomDeviceMersenne());
       break;
@@ -467,7 +473,6 @@ void RandomGenerator::initialize(RandomType type) {
       _device.reset(new RandomDeviceCombined<600>("/dev/random"));
       break;
     }
-
 #endif
 
 #ifdef _WIN32
@@ -484,7 +489,10 @@ void RandomGenerator::initialize(RandomType type) {
   }
 }
 
-void RandomGenerator::shutdown() { _device.reset(nullptr); }
+void RandomGenerator::shutdown() {
+  // nothing to do...
+  // thread-local devices will be released when their respective threads terminate.
+}
 
 int16_t RandomGenerator::interval(int16_t left, int16_t right) {
   uint16_t value = static_cast<int16_t>(
@@ -495,13 +503,7 @@ int16_t RandomGenerator::interval(int16_t left, int16_t right) {
 }
 
 int32_t RandomGenerator::interval(int32_t left, int32_t right) {
-  MUTEX_LOCKER(locker, _lock);
-
-  if (_device == nullptr) {
-    THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_INTERNAL,
-                                   "random generator not initialized");
-  }
-
+  ensureDeviceIsInitialized();
   int32_t value = _device->interval(left, right);
   TRI_ASSERT(value >= left && value <= right);
   return value;
@@ -561,13 +563,7 @@ uint16_t RandomGenerator::interval(uint16_t right) {
 }
 
 uint32_t RandomGenerator::interval(uint32_t right) {
-  MUTEX_LOCKER(locker, _lock);
-
-  if (_device == nullptr) {
-    THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_INTERNAL,
-                                   "random generator not initialized");
-  }
-
+  ensureDeviceIsInitialized();
   uint32_t value = _device->interval(static_cast<uint32_t>(0), right);
   TRI_ASSERT(value <= right);
   return value;
@@ -603,10 +599,7 @@ uint64_t RandomGenerator::interval(uint64_t right) {
 }
 
 void RandomGenerator::seed(uint64_t seed) {
-  MUTEX_LOCKER(locker, _lock);
-  if (!_device) {
-    throw std::runtime_error("Random device not yet initialized!");
-  }
+  ensureDeviceIsInitialized();
   if (RandomDeviceMersenne* dev = dynamic_cast<RandomDeviceMersenne*>(_device.get())) {
     dev->seed(seed);
     return;
diff --git a/lib/Random/RandomGenerator.h b/lib/Random/RandomGenerator.h
index ce21de02df..c871e84749 100644
--- a/lib/Random/RandomGenerator.h
+++ b/lib/Random/RandomGenerator.h
@@ -93,8 +93,10 @@ class RandomGenerator {
   static uint64_t interval(uint64_t);
 
  private:
-  static Mutex _lock;
-  static std::unique_ptr<RandomDevice> _device;
+  static void ensureDeviceIsInitialized();
+
+  static RandomType _type;
+  static thread_local std::unique_ptr<RandomDevice> _device;
 };
 }  // namespace arangodb