From 53c00841fc0d892bf43cda60e3ea2f05c4362b32 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Thu, 8 Sep 2022 18:32:26 +0300
Subject: [PATCH] Add support for BOOST_SYSTEM_DISABLE_THREADS (refs #92)

---
 include/boost/system/detail/config.hpp              |  8 +++++++-
 include/boost/system/detail/error_category_impl.hpp | 11 ++++++++++-
 test/CMakeLists.txt                                 |  1 +
 test/Jamfile.v2                                     |  1 +
 4 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/include/boost/system/detail/config.hpp b/include/boost/system/detail/config.hpp
index ad958bc..2dbb2f9 100644
--- a/include/boost/system/detail/config.hpp
+++ b/include/boost/system/detail/config.hpp
@@ -12,8 +12,14 @@
 #include <boost/config/workaround.hpp>
 
 // BOOST_SYSTEM_HAS_SYSTEM_ERROR
+//
+// The macro BOOST_SYSTEM_DISABLE_THREADS can be defined on configurations
+// that provide <system_error> and <atomic>, but not <mutex>, such as the
+// single-threaded libstdc++.
+//
+// https://github.com/boostorg/system/issues/92
 
-#if !defined(BOOST_NO_CXX11_HDR_SYSTEM_ERROR) && !defined(BOOST_NO_CXX11_HDR_ATOMIC) && !defined(BOOST_NO_CXX11_HDR_MUTEX)
+#if !defined(BOOST_NO_CXX11_HDR_SYSTEM_ERROR) && !defined(BOOST_NO_CXX11_HDR_ATOMIC) && ( !defined(BOOST_NO_CXX11_HDR_MUTEX) || defined(BOOST_SYSTEM_DISABLE_THREADS) )
 # define BOOST_SYSTEM_HAS_SYSTEM_ERROR
 #endif
 
diff --git a/include/boost/system/detail/error_category_impl.hpp b/include/boost/system/detail/error_category_impl.hpp
index 982c667..904a3a6 100644
--- a/include/boost/system/detail/error_category_impl.hpp
+++ b/include/boost/system/detail/error_category_impl.hpp
@@ -98,14 +98,19 @@ inline char const * error_category::message( int ev, char * buffer, std::size_t
 #if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
 
 #include <boost/system/detail/std_category_impl.hpp>
-#include <mutex>
 #include <new>
 
+#if !defined(BOOST_SYSTEM_DISABLE_THREADS)
+# include <mutex>
+#endif
+
 namespace boost
 {
 namespace system
 {
 
+#if !defined(BOOST_SYSTEM_DISABLE_THREADS)
+
 namespace detail
 {
 
@@ -118,6 +123,8 @@ template<class T> std::mutex stdcat_mx_holder<T>::mx_;
 
 } // namespace detail
 
+#endif
+
 inline void error_category::init_stdcat() const
 {
     static_assert( sizeof( stdcat_ ) >= sizeof( boost::system::detail::std_category ), "sizeof(stdcat_) is not enough for std_category" );
@@ -130,7 +137,9 @@ inline void error_category::init_stdcat() const
 
 #endif
 
+#if !defined(BOOST_SYSTEM_DISABLE_THREADS)
     std::lock_guard<std::mutex> lk( boost::system::detail::stdcat_mx_holder<>::mx_ );
+#endif
 
     if( sc_init_.load( std::memory_order_acquire ) == 0 )
     {
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 172e9eb..55efd27 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -15,6 +15,7 @@ macro(system_run s1)
   boost_test(SOURCES ${s1} ${ARGN})
   boost_test(SOURCES ${s1} ${ARGN} COMPILE_DEFINITIONS BOOST_NO_ANSI_APIS NAME ${n1}_no_ansi)
   boost_test(SOURCES ${s1} ${ARGN} COMPILE_DEFINITIONS BOOST_SYSTEM_USE_UTF8 NAME ${n1}_utf8)
+  boost_test(SOURCES ${s1} ${ARGN} COMPILE_DEFINITIONS BOOST_SYSTEM_DISABLE_THREADS NAME ${n1}_nthr)
 
 endmacro()
 
diff --git a/test/Jamfile.v2 b/test/Jamfile.v2
index d930c02..d110d39 100644
--- a/test/Jamfile.v2
+++ b/test/Jamfile.v2
@@ -33,6 +33,7 @@ rule system-run ( sources + )
     result += [ run $(sources) : : : <library>/boost/system//boost_system <link>shared : $(sources[1]:B)_shared ] ;
     result += [ run $(sources) : : : <define>BOOST_NO_ANSI_APIS : $(sources[1]:B)_no_ansi ] ;
     result += [ run $(sources) : : : <define>BOOST_SYSTEM_USE_UTF8 : $(sources[1]:B)_utf8 ] ;
+    result += [ run $(sources) : : : <define>BOOST_SYSTEM_DISABLE_THREADS : $(sources[1]:B)_nthr ] ;
 
     return $(result) ;
 }