diff --git a/include/boost/smart_ptr/detail/sp_thread_pause.hpp b/include/boost/smart_ptr/detail/sp_thread_pause.hpp
new file mode 100644
index 0000000..2cddd90
--- /dev/null
+++ b/include/boost/smart_ptr/detail/sp_thread_pause.hpp
@@ -0,0 +1,51 @@
+#ifndef BOOST_SMART_PTR_DETAIL_SP_THREAD_PAUSE_HPP_INCLUDED
+#define BOOST_SMART_PTR_DETAIL_SP_THREAD_PAUSE_HPP_INCLUDED
+
+// MS compatible compilers support #pragma once
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1020)
+# pragma once
+#endif
+
+// boost/smart_ptr/detail/sp_thread_pause.hpp
+//
+// inline void bost::detail::sp_thread_pause();
+//
+//   Emits a "pause" instruction.
+//
+// Copyright 2008, 2020 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0
+// https://www.boost.org/LICENSE_1_0.txt
+
+#if defined(_MSC_VER) && _MSC_VER >= 1310 && ( defined(_M_IX86) || defined(_M_X64) ) && !defined(__c2__)
+
+extern "C" void _mm_pause();
+
+#define BOOST_SP_PAUSE _mm_pause();
+
+#elif defined(__GNUC__) && ( defined(__i386__) || defined(__x86_64__) )
+
+#define BOOST_SP_PAUSE __asm__ __volatile__( "rep; nop" : : : "memory" );
+
+#else
+
+#define BOOST_SP_PAUSE
+
+#endif
+
+namespace boost
+{
+namespace detail
+{
+
+inline void sp_thread_pause()
+{
+    BOOST_SP_PAUSE
+}
+
+} // namespace detail
+} // namespace boost
+
+#undef BOOST_SP_PAUSE
+
+#endif // #ifndef BOOST_SMART_PTR_DETAIL_SP_THREAD_PAUSE_HPP_INCLUDED
diff --git a/include/boost/smart_ptr/detail/sp_thread_sleep.hpp b/include/boost/smart_ptr/detail/sp_thread_sleep.hpp
new file mode 100644
index 0000000..ff1d168
--- /dev/null
+++ b/include/boost/smart_ptr/detail/sp_thread_sleep.hpp
@@ -0,0 +1,104 @@
+#ifndef BOOST_SMART_PTR_DETAIL_SP_THREAD_SLEEP_HPP_INCLUDED
+#define BOOST_SMART_PTR_DETAIL_SP_THREAD_SLEEP_HPP_INCLUDED
+
+// MS compatible compilers support #pragma once
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1020)
+# pragma once
+#endif
+
+// boost/smart_ptr/detail/sp_thread_sleep.hpp
+//
+// inline void bost::detail::sp_thread_sleep();
+//
+//   Cease execution for a while to yield to other threads,
+//   as if by calling nanosleep() with an appropriate interval.
+//
+// Copyright 2008, 2020 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if defined( WIN32 ) || defined( _WIN32 ) || defined( __WIN32__ ) || defined( __CYGWIN__ )
+
+#if defined(BOOST_SP_REPORT_IMPLEMENTATION)
+  BOOST_PRAGMA_MESSAGE("Using Sleep(1) in sp_thread_sleep")
+#endif
+
+#include <boost/smart_ptr/detail/sp_win32_sleep.hpp>
+
+namespace boost
+{
+
+namespace detail
+{
+
+inline void sp_thread_sleep()
+{
+    Sleep( 1 );
+}
+
+} // namespace detail
+
+} // namespace boost
+
+#elif defined(BOOST_HAS_NANOSLEEP)
+
+#if defined(BOOST_SP_REPORT_IMPLEMENTATION)
+  BOOST_PRAGMA_MESSAGE("Using nanosleep() in sp_thread_sleep")
+#endif
+
+#include <time.h>
+
+namespace boost
+{
+
+namespace detail
+{
+
+inline void sp_thread_sleep()
+{
+    // g++ -Wextra warns on {} or {0}
+    struct timespec rqtp = { 0, 0 };
+
+    // POSIX says that timespec has tv_sec and tv_nsec
+    // But it doesn't guarantee order or placement
+
+    rqtp.tv_sec = 0;
+    rqtp.tv_nsec = 1000;
+
+    nanosleep( &rqtp, 0 );
+}
+
+} // namespace detail
+
+} // namespace boost
+
+#else
+
+#if defined(BOOST_SP_REPORT_IMPLEMENTATION)
+  BOOST_PRAGMA_MESSAGE("Using sp_thread_yield() in sp_thread_sleep")
+#endif
+
+#include <boost/smart_ptr/detail/sp_thread_yield.hpp>
+
+namespace boost
+{
+
+namespace detail
+{
+
+inline void sp_thread_sleep()
+{
+    sp_thread_yield();
+}
+
+} // namespace detail
+
+} // namespace boost
+
+#endif
+
+#endif // #ifndef BOOST_SMART_PTR_DETAIL_SP_THREAD_SLEEP_HPP_INCLUDED
diff --git a/include/boost/smart_ptr/detail/sp_thread_yield.hpp b/include/boost/smart_ptr/detail/sp_thread_yield.hpp
new file mode 100644
index 0000000..9a221cc
--- /dev/null
+++ b/include/boost/smart_ptr/detail/sp_thread_yield.hpp
@@ -0,0 +1,100 @@
+#ifndef BOOST_SMART_PTR_DETAIL_SP_THREAD_YIELD_HPP_INCLUDED
+#define BOOST_SMART_PTR_DETAIL_SP_THREAD_YIELD_HPP_INCLUDED
+
+// MS compatible compilers support #pragma once
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1020)
+# pragma once
+#endif
+
+// boost/smart_ptr/detail/sp_thread_yield.hpp
+//
+// inline void bost::detail::sp_thread_yield();
+//
+//   Gives up the remainder of the time slice,
+//   as if by calling sched_yield().
+//
+// Copyright 2008, 2020 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if defined( WIN32 ) || defined( _WIN32 ) || defined( __WIN32__ ) || defined( __CYGWIN__ )
+
+#if defined(BOOST_SP_REPORT_IMPLEMENTATION)
+  BOOST_PRAGMA_MESSAGE("Using Sleep(0) in sp_thread_yield")
+#endif
+
+#include <boost/smart_ptr/detail/sp_win32_sleep.hpp>
+
+namespace boost
+{
+
+namespace detail
+{
+
+inline void sp_thread_yield()
+{
+    Sleep( 0 );
+}
+
+} // namespace detail
+
+} // namespace boost
+
+#elif defined(BOOST_HAS_SCHED_YIELD)
+
+#if defined(BOOST_SP_REPORT_IMPLEMENTATION)
+  BOOST_PRAGMA_MESSAGE("Using sched_yield() in sp_thread_yield")
+#endif
+
+#ifndef _AIX
+# include <sched.h>
+#else
+  // AIX's sched.h defines ::var which sometimes conflicts with Lambda's var
+  extern "C" int sched_yield(void);
+#endif
+
+namespace boost
+{
+
+namespace detail
+{
+
+inline void sp_thread_yield()
+{
+    sched_yield();
+}
+
+} // namespace detail
+
+} // namespace boost
+
+#else
+
+#if defined(BOOST_SP_REPORT_IMPLEMENTATION)
+  BOOST_PRAGMA_MESSAGE("Using sp_thread_pause() in sp_thread_yield")
+#endif
+
+#include <boost/smart_ptr/detail/sp_thread_pause.hpp>
+
+namespace boost
+{
+
+namespace detail
+{
+
+inline void sp_thread_yield()
+{
+    sp_thread_pause();
+}
+
+} // namespace detail
+
+} // namespace boost
+
+#endif
+
+#endif // #ifndef BOOST_SMART_PTR_DETAIL_SP_THREAD_YIELD_HPP_INCLUDED
diff --git a/include/boost/smart_ptr/detail/sp_win32_sleep.hpp b/include/boost/smart_ptr/detail/sp_win32_sleep.hpp
new file mode 100644
index 0000000..139a569
--- /dev/null
+++ b/include/boost/smart_ptr/detail/sp_win32_sleep.hpp
@@ -0,0 +1,49 @@
+#ifndef BOOST_SMART_PTR_DETAIL_SP_WIN32_SLEEP_HPP_INCLUDED
+#define BOOST_SMART_PTR_DETAIL_SP_WIN32_SLEEP_HPP_INCLUDED
+
+// MS compatible compilers support #pragma once
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1020)
+# pragma once
+#endif
+
+// boost/smart_ptr/detail/sp_win32_sleep.hpp
+//
+// Declares the Win32 Sleep() function.
+//
+// Copyright 2008, 2020 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0
+// https://www.boost.org/LICENSE_1_0.txt
+
+#if defined( BOOST_USE_WINDOWS_H )
+# include <windows.h>
+#endif
+
+namespace boost
+{
+namespace detail
+{
+
+#if !defined( BOOST_USE_WINDOWS_H )
+
+#if defined(__clang__) && defined(__x86_64__)
+// clang x64 warns that __stdcall is ignored
+# define BOOST_SP_STDCALL
+#else
+# define BOOST_SP_STDCALL __stdcall
+#endif
+
+#if defined(__LP64__) // Cygwin 64
+  extern "C" __declspec(dllimport) void BOOST_SP_STDCALL Sleep( unsigned int ms );
+#else
+  extern "C" __declspec(dllimport) void BOOST_SP_STDCALL Sleep( unsigned long ms );
+#endif
+
+#undef BOOST_SP_STDCALL
+
+#endif // !defined( BOOST_USE_WINDOWS_H )
+
+} // namespace detail
+} // namespace boost
+
+#endif // #ifndef BOOST_SMART_PTR_DETAIL_SP_WIN32_SLEEP_HPP_INCLUDED
diff --git a/include/boost/smart_ptr/detail/yield_k.hpp b/include/boost/smart_ptr/detail/yield_k.hpp
index 8f52a58..d9a1b46 100644
--- a/include/boost/smart_ptr/detail/yield_k.hpp
+++ b/include/boost/smart_ptr/detail/yield_k.hpp
@@ -7,50 +7,21 @@
 # pragma once
 #endif
 
+// boost/smart_ptr/detail/yield_k.hpp
 //
-//  yield_k.hpp
+// Copyright 2008, 2020 Peter Dimov
 //
-//  Copyright (c) 2008 Peter Dimov
+// inline void boost::detail::yield( unsigned k );
 //
-//  void yield( unsigned k );
-//
-//  Typical use:
-//
-//  for( unsigned k = 0; !try_lock(); ++k ) yield( k );
-//
-//  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
+//   Typical use:
+//   for( unsigned k = 0; !try_lock(); ++k ) yield( k );
 //
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
 
+#include <boost/smart_ptr/detail/sp_thread_pause.hpp>
+#include <boost/smart_ptr/detail/sp_thread_sleep.hpp>
 #include <boost/config.hpp>
-#include <boost/config/pragma_message.hpp>
-
-// BOOST_SMT_PAUSE
-
-#if defined(_MSC_VER) && _MSC_VER >= 1310 && ( defined(_M_IX86) || defined(_M_X64) ) && !defined(__c2__)
-
-extern "C" void _mm_pause();
-
-#define BOOST_SMT_PAUSE _mm_pause();
-
-#elif defined(__GNUC__) && ( defined(__i386__) || defined(__x86_64__) )
-
-#define BOOST_SMT_PAUSE __asm__ __volatile__( "rep; nop" : : : "memory" );
-
-#else
-
-#define BOOST_SMT_PAUSE
-
-#endif
-
-//
-
-#if defined( WIN32 ) || defined( _WIN32 ) || defined( __WIN32__ ) || defined( __CYGWIN__ )
-
-#if defined( BOOST_USE_WINDOWS_H )
-# include <windows.h>
-#endif
 
 namespace boost
 {
@@ -58,133 +29,14 @@ namespace boost
 namespace detail
 {
 
-#if !defined( BOOST_USE_WINDOWS_H )
-
-#if defined(__clang__) && defined(__x86_64__)
-// clang x64 warns that __stdcall is ignored
-# define BOOST_SP_STDCALL
-#else
-# define BOOST_SP_STDCALL __stdcall
-#endif
-
-#if defined(__LP64__) // Cygwin 64
-  extern "C" __declspec(dllimport) void BOOST_SP_STDCALL Sleep( unsigned int ms );
-#else
-  extern "C" __declspec(dllimport) void BOOST_SP_STDCALL Sleep( unsigned long ms );
-#endif
-
-#undef BOOST_SP_STDCALL
-
-#endif // !defined( BOOST_USE_WINDOWS_H )
-
-#if defined(BOOST_SP_REPORT_IMPLEMENTATION)
-  BOOST_PRAGMA_MESSAGE("Using Win32 yield_k")
-#endif
-
-inline void sp_thread_yield()
+inline void yield( unsigned k )
 {
-    Sleep( 0 );
-}
+    // Experiments on Windows and Fedora 32 show that a single pause,
+    // followed by an immediate sp_thread_sleep(), is best.
 
-inline void sp_thread_sleep()
-{
-    Sleep( 1 );
-}
-
-} // namespace detail
-
-} // namespace boost
-
-#elif defined( BOOST_HAS_PTHREADS )
-
-#ifndef _AIX
-#include <sched.h>
-#else
-    // AIX's sched.h defines ::var which sometimes conflicts with Lambda's var
-    extern "C" int sched_yield(void);
-#endif
-
-#include <time.h>
-
-namespace boost
-{
-
-namespace detail
-{
-
-#if defined(BOOST_SP_REPORT_IMPLEMENTATION)
-  BOOST_PRAGMA_MESSAGE("Using POSIX yield_k")
-#endif
-
-inline void sp_thread_yield()
-{
-    sched_yield();
-}
-
-inline void sp_thread_sleep()
-{
-    // g++ -Wextra warns on {} or {0}
-    struct timespec rqtp = { 0, 0 };
-
-    // POSIX says that timespec has tv_sec and tv_nsec
-    // But it doesn't guarantee order or placement
-
-    rqtp.tv_sec = 0;
-    rqtp.tv_nsec = 1000;
-
-    nanosleep( &rqtp, 0 );
-}
-
-} // namespace detail
-
-} // namespace boost
-
-#else
-
-#if defined(BOOST_SP_REPORT_IMPLEMENTATION)
-  BOOST_PRAGMA_MESSAGE("Using empty yield_k")
-#endif
-
-namespace boost
-{
-
-namespace detail
-{
-
-inline void sp_thread_yield()
-{
-    BOOST_SMT_PAUSE
-}
-
-inline void sp_thread_sleep()
-{
-    BOOST_SMT_PAUSE
-}
-
-} // namespace detail
-
-} // namespace boost
-
-#endif
-
-namespace boost
-{
-
-namespace detail
-{
-
-inline void yield( unsigned k ) BOOST_NOEXCEPT
-{
-    // Experiments show that a simple sp_thread_sleep() here is best;
-    // leave a few pause instructions out of mostly superstition.
-    // (These are verified to not degrade performance.)
-    //
-    // There seems to be no benefit from calling sp_thread_yield()
-    // at any time.
-
-    if( k < 8 )
+    if( k == 0 )
     {
-        BOOST_SMT_PAUSE
+        sp_thread_pause();
     }
     else
     {