diff --git a/include/boost/smart_ptr/detail/spinlock_gcc_arm.hpp b/include/boost/smart_ptr/detail/spinlock_gcc_arm.hpp
new file mode 100644
index 0000000..e618f6e
--- /dev/null
+++ b/include/boost/smart_ptr/detail/spinlock_gcc_arm.hpp
@@ -0,0 +1,128 @@
+#ifndef BOOST_SMART_PTR_DETAIL_SPINLOCK_GCC_ARM_HPP_INCLUDED
+#define BOOST_SMART_PTR_DETAIL_SPINLOCK_GCC_ARM_HPP_INCLUDED
+
+//
+//  Copyright (c) 2008, 2011 Peter Dimov
+//
+//  Distributed under the Boost Software License, Version 1.0.
+//  See accompanying file LICENSE_1_0.txt or copy at
+//  http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/smart_ptr/detail/yield_k.hpp>
+
+#if defined(BOOST_SP_REPORT_IMPLEMENTATION)
+
+#include <boost/config/pragma_message.hpp>
+BOOST_PRAGMA_MESSAGE("Using g++/ARM spinlock")
+
+#endif
+
+#if defined(__ARM_ARCH_7__) || defined(__ARM_ARCH_7A__) || defined(__ARM_ARCH_7R__) || defined(__ARM_ARCH_7M__) || defined(__ARM_ARCH_7EM__) || defined(__ARM_ARCH_7S__)
+
+# define BOOST_SP_ARM_BARRIER "dmb"
+# define BOOST_SP_ARM_HAS_LDREX
+
+#elif defined(__ARM_ARCH_6__) || defined(__ARM_ARCH_6J__) || defined(__ARM_ARCH_6K__) || defined(__ARM_ARCH_6Z__) || defined(__ARM_ARCH_6ZK__) || defined(__ARM_ARCH_6T2__)
+
+# define BOOST_SP_ARM_BARRIER "mcr p15, 0, r0, c7, c10, 5"
+# define BOOST_SP_ARM_HAS_LDREX
+
+#else
+
+# define BOOST_SP_ARM_BARRIER ""
+
+#endif
+
+namespace boost
+{
+
+namespace detail
+{
+
+class spinlock
+{
+public:
+
+    int v_;
+
+public:
+
+    bool try_lock()
+    {
+        int r;
+
+#ifdef BOOST_SP_ARM_HAS_LDREX
+
+        __asm__ __volatile__(
+            "ldrex %0, [%2]; \n"
+            "cmp %0, %1; \n"
+            "strexne %0, %1, [%2]; \n"
+            BOOST_SP_ARM_BARRIER :
+            "=&r"( r ): // outputs
+            "r"( 1 ), "r"( &v_ ): // inputs
+            "memory", "cc" );
+
+#else
+
+        __asm__ __volatile__(
+            "swp %0, %1, [%2];\n"
+            BOOST_SP_ARM_BARRIER :
+            "=&r"( r ): // outputs
+            "r"( 1 ), "r"( &v_ ): // inputs
+            "memory", "cc" );
+
+#endif
+
+        return r == 0;
+    }
+
+    void lock()
+    {
+        for( unsigned k = 0; !try_lock(); ++k )
+        {
+            boost::detail::yield( k );
+        }
+    }
+
+    void unlock()
+    {
+        __asm__ __volatile__( BOOST_SP_ARM_BARRIER ::: "memory" );
+        *const_cast< int volatile* >( &v_ ) = 0;
+        __asm__ __volatile__( BOOST_SP_ARM_BARRIER ::: "memory" );
+    }
+
+public:
+
+    class scoped_lock
+    {
+    private:
+
+        spinlock & sp_;
+
+        scoped_lock( scoped_lock const & );
+        scoped_lock & operator=( scoped_lock const & );
+
+    public:
+
+        explicit scoped_lock( spinlock & sp ): sp_( sp )
+        {
+            sp.lock();
+        }
+
+        ~scoped_lock()
+        {
+            sp_.unlock();
+        }
+    };
+};
+
+} // namespace detail
+} // namespace boost
+
+#define BOOST_DETAIL_SPINLOCK_INIT {0}
+
+#undef BOOST_SP_ARM_BARRIER
+#undef BOOST_SP_ARM_HAS_LDREX
+
+#endif // #ifndef BOOST_SMART_PTR_DETAIL_SPINLOCK_GCC_ARM_HPP_INCLUDED
diff --git a/include/boost/smart_ptr/detail/spinlock_gcc_atomic.hpp b/include/boost/smart_ptr/detail/spinlock_gcc_atomic.hpp
new file mode 100644
index 0000000..d87b844
--- /dev/null
+++ b/include/boost/smart_ptr/detail/spinlock_gcc_atomic.hpp
@@ -0,0 +1,94 @@
+#ifndef BOOST_SMART_PTR_DETAIL_SPINLOCK_GCC_ATOMIC_HPP_INCLUDED
+#define BOOST_SMART_PTR_DETAIL_SPINLOCK_GCC_ATOMIC_HPP_INCLUDED
+
+// MS compatible compilers support #pragma once
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1020)
+# pragma once
+#endif
+
+// Copyright 2008, 2020 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/smart_ptr/detail/yield_k.hpp>
+
+#if defined(BOOST_SP_REPORT_IMPLEMENTATION)
+
+#include <boost/config/pragma_message.hpp>
+BOOST_PRAGMA_MESSAGE("Using __atomic spinlock")
+
+#endif
+
+namespace boost
+{
+
+namespace detail
+{
+
+class spinlock
+{
+public:
+
+    // `bool` alignment is required for Apple PPC32
+    // https://github.com/boostorg/smart_ptr/issues/105
+    // https://github.com/PurpleI2P/i2pd/issues/1726
+    // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107590
+
+    union
+    {
+        unsigned char v_;
+        bool align_;
+    };
+
+public:
+
+    bool try_lock()
+    {
+        return __atomic_test_and_set( &v_, __ATOMIC_ACQUIRE ) == 0;
+    }
+
+    void lock()
+    {
+        for( unsigned k = 0; !try_lock(); ++k )
+        {
+            boost::detail::yield( k );
+        }
+    }
+
+    void unlock()
+    {
+        __atomic_clear( &v_, __ATOMIC_RELEASE );
+    }
+
+public:
+
+    class scoped_lock
+    {
+    private:
+
+        spinlock & sp_;
+
+        scoped_lock( scoped_lock const & );
+        scoped_lock & operator=( scoped_lock const & );
+
+    public:
+
+        explicit scoped_lock( spinlock & sp ): sp_( sp )
+        {
+            sp.lock();
+        }
+
+        ~scoped_lock()
+        {
+            sp_.unlock();
+        }
+    };
+};
+
+} // namespace detail
+} // namespace boost
+
+#define BOOST_DETAIL_SPINLOCK_INIT {{0}}
+
+#endif // #ifndef BOOST_SMART_PTR_DETAIL_SPINLOCK_GCC_ATOMIC_HPP_INCLUDED
diff --git a/include/boost/smart_ptr/detail/spinlock_nt.hpp b/include/boost/smart_ptr/detail/spinlock_nt.hpp
new file mode 100644
index 0000000..ce23761
--- /dev/null
+++ b/include/boost/smart_ptr/detail/spinlock_nt.hpp
@@ -0,0 +1,96 @@
+#ifndef BOOST_SMART_PTR_DETAIL_SPINLOCK_NT_HPP_INCLUDED
+#define BOOST_SMART_PTR_DETAIL_SPINLOCK_NT_HPP_INCLUDED
+
+// MS compatible compilers support #pragma once
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1020)
+# pragma once
+#endif
+
+//
+//  Copyright (c) 2008 Peter Dimov
+//
+//  Distributed under the Boost Software License, Version 1.0.
+//  See accompanying file LICENSE_1_0.txt or copy at
+//  http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/assert.hpp>
+
+#if defined(BOOST_SP_REPORT_IMPLEMENTATION)
+
+#include <boost/config/pragma_message.hpp>
+BOOST_PRAGMA_MESSAGE("Using single-threaded spinlock emulation")
+
+#endif
+
+namespace boost
+{
+
+namespace detail
+{
+
+class spinlock
+{
+public:
+
+    bool locked_;
+
+public:
+
+    inline bool try_lock()
+    {
+        if( locked_ )
+        {
+            return false;
+        }
+        else
+        {
+            locked_ = true;
+            return true;
+        }
+    }
+
+    inline void lock()
+    {
+        BOOST_ASSERT( !locked_ );
+        locked_ = true;
+    }
+
+    inline void unlock()
+    {
+        BOOST_ASSERT( locked_ );
+        locked_ = false;
+    }
+
+public:
+
+    class scoped_lock
+    {
+    private:
+
+        spinlock & sp_;
+
+        scoped_lock( scoped_lock const & );
+        scoped_lock & operator=( scoped_lock const & );
+
+    public:
+
+        explicit scoped_lock( spinlock & sp ): sp_( sp )
+        {
+            sp.lock();
+        }
+
+        ~scoped_lock()
+        {
+            sp_.unlock();
+        }
+    };
+};
+
+} // namespace detail
+} // namespace boost
+
+#define BOOST_DETAIL_SPINLOCK_INIT { false }
+
+#endif // #ifndef BOOST_SMART_PTR_DETAIL_SPINLOCK_NT_HPP_INCLUDED
diff --git a/include/boost/smart_ptr/detail/spinlock_pt.hpp b/include/boost/smart_ptr/detail/spinlock_pt.hpp
new file mode 100644
index 0000000..a7f8a81
--- /dev/null
+++ b/include/boost/smart_ptr/detail/spinlock_pt.hpp
@@ -0,0 +1,86 @@
+#ifndef BOOST_SMART_PTR_DETAIL_SPINLOCK_PT_HPP_INCLUDED
+#define BOOST_SMART_PTR_DETAIL_SPINLOCK_PT_HPP_INCLUDED
+
+// MS compatible compilers support #pragma once
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1020)
+# pragma once
+#endif
+
+//
+//  Copyright (c) 2008 Peter Dimov
+//
+//  Distributed under the Boost Software License, Version 1.0.
+//  See accompanying file LICENSE_1_0.txt or copy at
+//  http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <pthread.h>
+
+#if defined(BOOST_SP_REPORT_IMPLEMENTATION)
+
+#include <boost/config/pragma_message.hpp>
+BOOST_PRAGMA_MESSAGE("Using pthread_mutex spinlock emulation")
+
+#endif
+
+namespace boost
+{
+
+namespace detail
+{
+
+class spinlock
+{
+public:
+
+    pthread_mutex_t v_;
+
+public:
+
+    bool try_lock()
+    {
+        return pthread_mutex_trylock( &v_ ) == 0;
+    }
+
+    void lock()
+    {
+        pthread_mutex_lock( &v_ );
+    }
+
+    void unlock()
+    {
+        pthread_mutex_unlock( &v_ );
+    }
+
+public:
+
+    class scoped_lock
+    {
+    private:
+
+        spinlock & sp_;
+
+        scoped_lock( scoped_lock const & );
+        scoped_lock & operator=( scoped_lock const & );
+
+    public:
+
+        explicit scoped_lock( spinlock & sp ): sp_( sp )
+        {
+            sp.lock();
+        }
+
+        ~scoped_lock()
+        {
+            sp_.unlock();
+        }
+    };
+};
+
+} // namespace detail
+} // namespace boost
+
+#define BOOST_DETAIL_SPINLOCK_INIT { PTHREAD_MUTEX_INITIALIZER }
+
+#endif // #ifndef BOOST_SMART_PTR_DETAIL_SPINLOCK_PT_HPP_INCLUDED
diff --git a/include/boost/smart_ptr/detail/spinlock_sync.hpp b/include/boost/smart_ptr/detail/spinlock_sync.hpp
new file mode 100644
index 0000000..cbfdd94
--- /dev/null
+++ b/include/boost/smart_ptr/detail/spinlock_sync.hpp
@@ -0,0 +1,94 @@
+#ifndef BOOST_SMART_PTR_DETAIL_SPINLOCK_SYNC_HPP_INCLUDED
+#define BOOST_SMART_PTR_DETAIL_SPINLOCK_SYNC_HPP_INCLUDED
+
+// MS compatible compilers support #pragma once
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1020)
+# pragma once
+#endif
+
+//
+//  Copyright (c) 2008 Peter Dimov
+//
+//  Distributed under the Boost Software License, Version 1.0.
+//  See accompanying file LICENSE_1_0.txt or copy at
+//  http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/smart_ptr/detail/yield_k.hpp>
+
+#if defined( __ia64__ ) && defined( __INTEL_COMPILER )
+# include <ia64intrin.h>
+#endif
+
+#if defined(BOOST_SP_REPORT_IMPLEMENTATION)
+
+#include <boost/config/pragma_message.hpp>
+BOOST_PRAGMA_MESSAGE("Using __sync spinlock")
+
+#endif
+
+namespace boost
+{
+
+namespace detail
+{
+
+class spinlock
+{
+public:
+
+    unsigned char v_;
+
+public:
+
+    bool try_lock()
+    {
+        int r = __sync_lock_test_and_set( &v_, 1 );
+        return r == 0;
+    }
+
+    void lock()
+    {
+        for( unsigned k = 0; !try_lock(); ++k )
+        {
+            boost::detail::yield( k );
+        }
+    }
+
+    void unlock()
+    {
+        __sync_lock_release( &v_ );
+    }
+
+public:
+
+    class scoped_lock
+    {
+    private:
+
+        spinlock & sp_;
+
+        scoped_lock( scoped_lock const & );
+        scoped_lock & operator=( scoped_lock const & );
+
+    public:
+
+        explicit scoped_lock( spinlock & sp ): sp_( sp )
+        {
+            sp.lock();
+        }
+
+        ~scoped_lock()
+        {
+            sp_.unlock();
+        }
+    };
+};
+
+} // namespace detail
+} // namespace boost
+
+#define BOOST_DETAIL_SPINLOCK_INIT {0}
+
+#endif // #ifndef BOOST_SMART_PTR_DETAIL_SPINLOCK_SYNC_HPP_INCLUDED
diff --git a/include/boost/smart_ptr/detail/spinlock_w32.hpp b/include/boost/smart_ptr/detail/spinlock_w32.hpp
new file mode 100644
index 0000000..39092ce
--- /dev/null
+++ b/include/boost/smart_ptr/detail/spinlock_w32.hpp
@@ -0,0 +1,120 @@
+#ifndef BOOST_SMART_PTR_DETAIL_SPINLOCK_W32_HPP_INCLUDED
+#define BOOST_SMART_PTR_DETAIL_SPINLOCK_W32_HPP_INCLUDED
+
+// MS compatible compilers support #pragma once
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1020)
+# pragma once
+#endif
+
+//
+//  Copyright (c) 2008 Peter Dimov
+//
+//  Distributed under the Boost Software License, Version 1.0.
+//  See accompanying file LICENSE_1_0.txt or copy at
+//  http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/smart_ptr/detail/sp_interlocked.hpp>
+#include <boost/smart_ptr/detail/yield_k.hpp>
+
+#if defined(BOOST_SP_REPORT_IMPLEMENTATION)
+
+#include <boost/config/pragma_message.hpp>
+BOOST_PRAGMA_MESSAGE("Using Win32 spinlock")
+
+#endif
+
+// BOOST_COMPILER_FENCE
+
+#if defined(__INTEL_COMPILER)
+
+#define BOOST_COMPILER_FENCE __memory_barrier();
+
+#elif defined( _MSC_VER ) && _MSC_VER >= 1310
+
+extern "C" void _ReadWriteBarrier();
+#pragma intrinsic( _ReadWriteBarrier )
+
+#define BOOST_COMPILER_FENCE _ReadWriteBarrier();
+
+#elif defined(__GNUC__)
+
+#define BOOST_COMPILER_FENCE __asm__ __volatile__( "" : : : "memory" );
+
+#else
+
+#define BOOST_COMPILER_FENCE
+
+#endif
+
+//
+
+namespace boost
+{
+
+namespace detail
+{
+
+class spinlock
+{
+public:
+
+    long v_;
+
+public:
+
+    bool try_lock()
+    {
+        long r = BOOST_SP_INTERLOCKED_EXCHANGE( &v_, 1 );
+
+        BOOST_COMPILER_FENCE
+
+        return r == 0;
+    }
+
+    void lock()
+    {
+        for( unsigned k = 0; !try_lock(); ++k )
+        {
+            boost::detail::yield( k );
+        }
+    }
+
+    void unlock()
+    {
+        BOOST_COMPILER_FENCE
+        *const_cast< long volatile* >( &v_ ) = 0;
+    }
+
+public:
+
+    class scoped_lock
+    {
+    private:
+
+        spinlock & sp_;
+
+        scoped_lock( scoped_lock const & );
+        scoped_lock & operator=( scoped_lock const & );
+
+    public:
+
+        explicit scoped_lock( spinlock & sp ): sp_( sp )
+        {
+            sp.lock();
+        }
+
+        ~scoped_lock()
+        {
+            sp_.unlock();
+        }
+    };
+};
+
+} // namespace detail
+} // namespace boost
+
+#define BOOST_DETAIL_SPINLOCK_INIT {0}
+
+#endif // #ifndef BOOST_SMART_PTR_DETAIL_SPINLOCK_W32_HPP_INCLUDED