diff --git a/ostd/concurrency.hh b/ostd/concurrency.hh
index 3905124..1520bd2 100644
--- a/ostd/concurrency.hh
+++ b/ostd/concurrency.hh
@@ -148,18 +148,30 @@ struct basic_thread_scheduler: scheduler {
     }
 
     stack_context allocate_stack() {
-        std::lock_guard<std::mutex> l{p_lock};
-        return p_stacks.allocate();
+        if constexpr(!SA::is_thread_safe) {
+            std::lock_guard<std::mutex> l{p_lock};
+            return p_stacks.allocate();
+        } else {
+            return p_stacks.allocate();
+        }
     }
 
     void deallocate_stack(stack_context &st) noexcept {
-        std::lock_guard<std::mutex> l{p_lock};
-        p_stacks.deallocate(st);
+        if constexpr(!SA::is_thread_safe) {
+            std::lock_guard<std::mutex> l{p_lock};
+            p_stacks.deallocate(st);
+        } else {
+            p_stacks.deallocate();
+        }
     }
 
     void reserve_stacks(size_t n) {
-        std::lock_guard<std::mutex> l{p_lock};
-        p_stacks.reserve(n);
+        if constexpr(!SA::is_thread_safe) {
+            std::lock_guard<std::mutex> l{p_lock};
+            p_stacks.reserve(n);
+        } else {
+            p_stacks.reserve(n);
+        }
     }
 
 private:
@@ -509,18 +521,30 @@ public:
     }
 
     stack_context allocate_stack() {
-        std::lock_guard<std::mutex> l{p_lock};
-        return p_stacks.allocate();
+        if constexpr(!SA::is_thread_safe) {
+            std::lock_guard<std::mutex> l{p_lock};
+            return p_stacks.allocate();
+        } else {
+            return p_stacks.allocate();
+        }
     }
 
     void deallocate_stack(stack_context &st) noexcept {
-        std::lock_guard<std::mutex> l{p_lock};
-        p_stacks.deallocate(st);
+        if constexpr(!SA::is_thread_safe) {
+            std::lock_guard<std::mutex> l{p_lock};
+            p_stacks.deallocate(st);
+        } else {
+            p_stacks.deallocate();
+        }
     }
 
     void reserve_stacks(size_t n) {
-        std::lock_guard<std::mutex> l{p_lock};
-        p_stacks.reserve(n);
+        if constexpr(!SA::is_thread_safe) {
+            std::lock_guard<std::mutex> l{p_lock};
+            p_stacks.reserve(n);
+        } else {
+            p_stacks.reserve(n);
+        }
     }
 
 private:
diff --git a/ostd/context_stack.hh b/ostd/context_stack.hh
index 4f0803d..6fe0999 100644
--- a/ostd/context_stack.hh
+++ b/ostd/context_stack.hh
@@ -50,6 +50,7 @@ template<typename TR, bool Protected>
 struct basic_fixedsize_stack {
     using traits_type = TR;
     using allocator_type = basic_fixedsize_stack;
+    static constexpr bool is_thread_safe = true;
 
     basic_fixedsize_stack(size_t ss = TR::default_size()) noexcept:
         p_size(
@@ -127,6 +128,7 @@ public:
 
     using traits_type = TR;
     using allocator_type = allocator;
+    static constexpr bool is_thread_safe = false;
 
     basic_stack_pool(
         size_t ss = TR::default_size(), size_t cs = DEFAULT_CHUNK_SIZE