From a6848417fed706ec4f89a589c2ea9aa54eb39829 Mon Sep 17 00:00:00 2001
From: kulikov <kulikov@yandex-team.com>
Date: Mon, 8 Jun 2026 20:33:12 +0300
Subject: Improve TGenericLocalValue, allow mixed thread-fiber-etc values

Make generic local values more safe and usable:

- instead of factory, register fiber/coroutine-aware "GLS (general local storage) contexts";
- put up to 4 (normally no more than 2 -- threads and one coroutine implementation) different "tls" variables into one generic, choose correct one from current execution context;
- suitable version of variable will be constructed on demand (no dependency from first usage);
- improve unit test too.
commit_hash:8586846a6a775bd66dffcdf58263f78042be2480
---
 library/cpp/threading/thread_local/generic.cpp | 65 ++++++++++++++++++++------
 1 file changed, 50 insertions(+), 15 deletions(-)

(limited to 'library/cpp/threading/thread_local/generic.cpp')

diff --git a/library/cpp/threading/thread_local/generic.cpp b/library/cpp/threading/thread_local/generic.cpp
index 79161a846da..eca63d76bc6 100644
--- a/library/cpp/threading/thread_local/generic.cpp
+++ b/library/cpp/threading/thread_local/generic.cpp
@@ -14,29 +14,64 @@ namespace {
         NThreading::TThreadLocalValue<TData, NThreading::EThreadLocalImpl::StdThreadLocal> Data_;
     };
 
-    std::atomic<size_t>& DefaultFactoryUsageCounter() {
-        static std::atomic<size_t> v;
-        return v;
-    }
+    class TThreadLocalContext
+        : public NThreading::IGLSContext
+    {
+        bool IsCurrent() const override {
+            return true;
+        }
 
-    auto& genericLocalStorageFactory() {
-        static NThreading::TGenericLocalStorageFactory factory = [] {
-            DefaultFactoryUsageCounter() += 1;
+        THolder<NThreading::IGenericLocalStorage> MakeStorage() const override {
             return MakeHolder<TThreadLocalStorage>();
-        };
+        }
+    };
+
+    class TContextRegistry {
+    public:
+        TContextRegistry() {
+            Register(MakeHolder<TThreadLocalContext>());
+        }
+
+        size_t Count() const {
+            return Count_.load();
+        }
 
-        return factory;
+        const NThreading::IGLSContext& Get(size_t index) const {
+            return *Contexts_[index];
+        }
+
+        void Register(THolder<NThreading::IGLSContext> context) {
+            with_lock (Lock_) {
+                const size_t index = Count_.load();
+                Y_ENSURE(index < NThreading::NDetail::MaxGLSContexts, "Too many generic local contexts registered");
+                Contexts_[index] = std::move(context);
+                Count_.store(index + 1);
+            }
+        }
+    private:
+        TAdaptiveLock Lock_;
+        std::atomic<size_t> Count_ = 0;
+        std::array<THolder<NThreading::IGLSContext>, NThreading::NDetail::MaxGLSContexts> Contexts_ = {};
+    };
+
+    TContextRegistry& Registry() {
+        static TContextRegistry registry;
+        return registry;
     }
 }
 
 namespace NThreading {
-    void SetGenericLocalStorageFactory(TGenericLocalStorageFactory factory) {
-        Y_ENSURE(DefaultFactoryUsageCounter() == 0, "There are some thread local values allocated with default factory");
-
-        genericLocalStorageFactory() = factory;
+    void RegisterGLSContext(THolder<IGLSContext> context) {
+        Registry().Register(std::move(context));
     }
 
-    THolder<IGenericLocalStorage> MakeGenericLocalStorage() {
-        return genericLocalStorageFactory()();
+    namespace NDetail {
+        size_t GLSContextCount() {
+            return Registry().Count();
+        }
+
+        const IGLSContext& GetGLSContext(size_t index) {
+            return Registry().Get(index);
+        }
     }
 }
-- 
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