diff --git a/include/libimp/construct.h b/include/libimp/construct.h
index 4b485b1..8d39dd7 100644
--- a/include/libimp/construct.h
+++ b/include/libimp/construct.h
@@ -45,6 +45,7 @@ auto construct(void *p, A &&... args)
 
 template <typename T>
 void *destroy(T *p) noexcept {
+  if (p == nullptr) return nullptr;
 #if defined(LIBIMP_CPP_17)
   std::destroy_at(p);
 #else
@@ -55,6 +56,7 @@ void *destroy(T *p) noexcept {
 
 template <typename T, std::size_t N>
 void *destroy(T (*p)[N]) noexcept {
+  if (p == nullptr) return nullptr;
 #if defined(LIBIMP_CPP_20)
   std::destroy_at(p);
 #elif defined(LIBIMP_CPP_17)
diff --git a/include/libipc/def.h b/include/libipc/def.h
index 0561ffe..6690155 100755
--- a/include/libipc/def.h
+++ b/include/libipc/def.h
@@ -6,8 +6,11 @@
  */
 #pragma once
 
-#include <cstddef>
+#include <cstddef>  // std::max_align_t
 #include <cstdint>
+#include <new>      // std::hardware_destructive_interference_size
+
+#include "libimp/detect_plat.h"
 
 #define LIBIPC_               ipc
 #define LIBIPC_NAMESPACE_BEG_ namespace LIBIPC_ {
@@ -35,4 +38,16 @@ struct mode {
   };
 };
 
+enum : std::size_t {
+  /// @brief Minimum offset between two objects to avoid false sharing.
+  /// @see https://en.cppreference.com/w/cpp/thread/hardware_destructive_interference_size
+  cache_line_size =
+#if defined(LIBIMP_CPP_17) && defined(__cpp_lib_hardware_interference_size)
+    ( std::hardware_destructive_interference_size < alignof(std::max_align_t) ) ? 64 
+    : std::hardware_destructive_interference_size,
+#else
+    64,
+#endif
+};
+
 LIBIPC_NAMESPACE_END_
diff --git a/src/libipc/concurrent.h b/src/libipc/concurrent.h
new file mode 100644
index 0000000..b7371db
--- /dev/null
+++ b/src/libipc/concurrent.h
@@ -0,0 +1,26 @@
+
+#include <cstdint>
+#include <limits>
+
+#include "libipc/def.h"
+
+LIBIPC_NAMESPACE_BEG_
+namespace concurrent {
+
+/// @brief The queue index type.
+using index_t = std::uint32_t;
+
+namespace state {
+
+/// @brief The state flag type for the queue element.
+using flag_t = std::uint64_t;
+
+enum : flag_t {
+  /// @brief The invalid state value.
+  invalid_value = (std::numeric_limits<flag_t>::max)(),
+};
+
+} // namespace state
+
+} // namespace concurrent
+LIBIPC_NAMESPACE_END_
diff --git a/test/test_ipc_concurrent.cpp b/test/test_ipc_concurrent.cpp
new file mode 100644
index 0000000..45cb1b6
--- /dev/null
+++ b/test/test_ipc_concurrent.cpp
@@ -0,0 +1,16 @@
+
+#include <iostream>
+#include <cstddef>
+
+#include "gtest/gtest.h"
+
+#include "libipc/concurrent.h"
+
+TEST(concurrent, cache_line_size) {
+  std::cout << ipc::cache_line_size << "\n";
+  EXPECT_TRUE(ipc::cache_line_size >= alignof(std::max_align_t));
+}
+
+TEST(concurrent, index_and_flag) {
+  EXPECT_TRUE(sizeof(ipc::concurrent::index_t) < sizeof(ipc::concurrent::state::flag_t));
+}
\ No newline at end of file