From 97de144574f683cff9e5bf9732eb2ff50ca7a2cf Mon Sep 17 00:00:00 2001
From: Sidorov Aleksei <aleksei.sidorov@huawei.com>
Date: Fri, 14 Apr 2023 21:40:04 +0800
Subject: [PATCH] [Runtime] Make global Random Engine for BuiltinsMath::Random

The profiler says that creating a random engine is a heavy operation.
That is why I created global Random Engine and put it in Ecma VM.

Signed-off-by: Sidorov Aleksei <aleksei.sidorov@huawei.com>
---
 runtime/builtins/builtins_math.cpp |  6 ++----
 runtime/ecma_vm.cpp                |  1 +
 runtime/ecma_vm.h                  | 16 ++++++++++++++++
 3 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/runtime/builtins/builtins_math.cpp b/runtime/builtins/builtins_math.cpp
index f58d08125..f76318f8f 100644
--- a/runtime/builtins/builtins_math.cpp
+++ b/runtime/builtins/builtins_math.cpp
@@ -565,11 +565,9 @@ JSTaggedValue BuiltinsMath::Random([[maybe_unused]] EcmaRuntimeCallInfo *argv)
 {
     ASSERT(argv);
     BUILTINS_API_TRACE(argv->GetThread(), Math, Random);
-    std::random_device rd;
-    std::default_random_engine engine(rd());
-    std::uniform_real_distribution<double> dis(0, std::random_device::max() - 1);
     // result range [0,1)
-    double result = dis(engine) / std::random_device::max();
+    std::uniform_real_distribution<double> dis(0.0, 1.0);
+    double result = dis(argv->GetThread()->GetEcmaVM()->GetRandomEngine());
     return GetTaggedDouble(result);
 }
 
diff --git a/runtime/ecma_vm.cpp b/runtime/ecma_vm.cpp
index 526474811..d78758796 100644
--- a/runtime/ecma_vm.cpp
+++ b/runtime/ecma_vm.cpp
@@ -171,6 +171,7 @@ EcmaVM::EcmaVM(JSRuntimeOptions options) : string_table_(new EcmaStringTable(thi
     rendezvous_ = allocator->New<Rendezvous>(this);
     notification_manager_ = allocator->New<RuntimeNotificationManager>(runtime->GetInternalAllocator());
     notification_manager_->SetRendezvous(rendezvous_);
+    InitializeRandomEngine();
 
     LanguageContext ctx = Runtime::GetCurrent()->GetLanguageContext(panda_file::SourceLang::ECMASCRIPT);
     mm_ = CreateMM(ctx, Runtime::GetCurrent()->GetInternalAllocator(), options_);
diff --git a/runtime/ecma_vm.h b/runtime/ecma_vm.h
index 9e7c26d68..a08f908cd 100644
--- a/runtime/ecma_vm.h
+++ b/runtime/ecma_vm.h
@@ -16,6 +16,7 @@
 #ifndef ECMASCRIPT_ECMA_VM_H
 #define ECMASCRIPT_ECMA_VM_H
 
+#include <random>
 #include <tuple>
 
 #include "include/mem/panda_containers.h"
@@ -467,6 +468,12 @@ public:
         return MEMBER_OFFSET(EcmaVM, global_env_);
     }
 
+    std::default_random_engine &GetRandomEngine()
+    {
+        ASSERT(random_engine_);
+        return *random_engine_;
+    }
+
 protected:
     bool CheckEntrypointSignature([[maybe_unused]] Method *entrypoint) override
     {
@@ -512,6 +519,13 @@ private:
     void LoadEcmaStdLib();
     const panda_file::File *GetLastLoadedPandaFile();
 
+    void InitializeRandomEngine()
+    {
+        ASSERT(!random_engine_);
+        std::random_device rd;
+        random_engine_.emplace(rd());
+    }
+
     NO_MOVE_SEMANTIC(EcmaVM);
     NO_COPY_SEMANTIC(EcmaVM);
 
@@ -575,6 +589,8 @@ private:
     HostPromiseRejectionTracker host_promise_rejection_tracker_ {nullptr};
     void *data_ {nullptr};
     PandaList<JSFinalizationRegistry *> finalization_registries_;
+    // optional for lazy initialization
+    std::optional<std::default_random_engine> random_engine_;
 
     friend class ObjectFactory;
     friend class panda::JSNApi;
-- 
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