boostorg · timblechmann · May 20, 2026 · May 20, 2026 · May 20, 2026 · May 20, 2026
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
@@ -151,8 +151,11 @@ jobs:
         if: env.B2_USE_CCACHE
         with:
           path: ~/.ccache
-          key: ${{matrix.os}}-${{matrix.container}}-${{matrix.compiler}}-${{github.sha}}
-          restore-keys: ${{matrix.os}}-${{matrix.container}}-${{matrix.compiler}}-
+          key: ccache-${{matrix.os}}-${{matrix.compiler}}-${{ hashFiles('**/*.cpp', '**/*.hpp', '**/*.c', '**/*.h') }}
+          restore-keys: |
+            ccache-${{matrix.os}}-${{matrix.compiler}}-
+            ccache-${{matrix.os}}-
+            ccache-
 
       - name: Install packages
         if: matrix.install
@@ -239,7 +242,7 @@ jobs:
             os: windows-2022
             supported: true
           - toolset: clang-win
-            cxxstd: "14,17,20,latest"
+            cxxstd: "latest,20,17,14"
             addrmd: 32,64
             os: windows-2022
             supported: true
@@ -353,6 +356,9 @@ jobs:
           git submodule update --init tools/boostdep
           python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" $LIBRARY
 
+          # HACK: boost.functional seems to be missing?
+          git submodule update --init libs/functional
+
       - name: Use library with add_subdirectory
         run: |
           cd ../boost-root/libs/$LIBRARY/test/cmake_subdir_test
@@ -409,6 +415,8 @@ jobs:
           git submodule update --init tools/boostdep
           python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" $LIBRARY
 
+          git submodule update --init libs/functional
+
       - name: Configure
         run: |
           cd ../boost-root
@@ -475,6 +483,8 @@ jobs:
           git submodule update --init tools/boostdep
           python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" $LIBRARY
 
+          git submodule update --init libs/functional
+
       - name: Configure
         run: |
           cd ../boost-root
@@ -527,6 +537,8 @@ jobs:
           git submodule update --init tools/boostdep
           python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" %LIBRARY%
 
+          git submodule update --init libs/functional
+
       - name: Use library with add_subdirectory (Debug)
         shell: cmd
         run: |
@@ -580,6 +592,8 @@ jobs:
           git submodule update --init tools/boostdep
           python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" %LIBRARY%
 
+          git submodule update --init libs/functional
+
       - name: Configure
         shell: cmd
         run: |
@@ -651,6 +665,8 @@ jobs:
           git submodule update --init tools/boostdep
           python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" %LIBRARY%
 
+          git submodule update --init libs/functional
+
       - name: Configure
         shell: cmd
         run: |

diff --git a/include/boost/lockfree/detail/freelist.hpp b/include/boost/lockfree/detail/freelist.hpp
@@ -39,7 +39,7 @@ namespace boost { namespace lockfree { namespace detail {
 template < typename T, typename Alloc = std::allocator< T > >
 class alignas( cacheline_bytes ) freelist_stack : Alloc
 {
-    struct freelist_node
+    struct BOOST_MAY_ALIAS freelist_node
     {
         tagged_ptr< freelist_node > next;
     };
@@ -395,7 +395,7 @@ struct runtime_sized_freelist_storage : boost::alignment::aligned_allocator_adap
 template < typename T, typename NodeStorage = runtime_sized_freelist_storage< T > >
 class fixed_size_freelist : NodeStorage
 {
-    struct freelist_node
+    struct BOOST_MAY_ALIAS freelist_node
     {
         tagged_index next;
     };

diff --git a/include/boost/lockfree/queue.hpp b/include/boost/lockfree/queue.hpp
@@ -104,7 +104,7 @@ class queue
     static constexpr bool node_based         = !( has_capacity || fixed_sized );
     static constexpr bool compile_time_sized = has_capacity;
 
-    struct alignas( detail::cacheline_bytes ) node
+    struct BOOST_MAY_ALIAS node
     {
         typedef typename detail::select_tagged_handle< node, node_based >::tagged_handle_type tagged_node_handle;
         typedef typename detail::select_tagged_handle< node, node_based >::handle_type        handle_type;
@@ -125,8 +125,8 @@ class queue
         node( void )
         {}
 
-        atomic< tagged_node_handle > next;
-        T                            data;
+        alignas( detail::cacheline_bytes ) atomic< tagged_node_handle > next;
+        T data;
     };
 
     typedef detail::extract_allocator_t< bound_args, node >                                              node_allocator;
@@ -177,8 +177,6 @@ class queue
         requires( has_capacity )
 #endif
         :
-        head_( tagged_node_handle( 0, 0 ) ),
-        tail_( tagged_node_handle( 0, 0 ) ),
         pool( node_allocator(), capacity )
     {
         // Don't use BOOST_STATIC_ASSERT() here since it will be evaluated when compiling
@@ -191,10 +189,13 @@ class queue
      *
      *  \pre Must specify a capacity<> argument
      * */
+#if !defined( BOOST_NO_CXX20_HDR_CONCEPTS )
+    template < typename U >
+        requires( has_capacity )
+#else
     template < typename U, typename Enabler = std::enable_if< has_capacity > >
+#endif
     explicit queue( typename boost::allocator_rebind< node_allocator, U >::type const& alloc ) :
-        head_( tagged_node_handle( 0, 0 ) ),
-        tail_( tagged_node_handle( 0, 0 ) ),
         pool( alloc, capacity )
     {
         initialize();
@@ -204,10 +205,14 @@ class queue
      *
      *  \pre Must specify a capacity<> argument
      * */
+#if !defined( BOOST_NO_CXX20_HDR_CONCEPTS )
+    explicit queue( allocator const& alloc )
+        requires( has_capacity )
+        :
+#else
     template < typename Enabler = std::enable_if< has_capacity > >
     explicit queue( allocator const& alloc ) :
-        head_( tagged_node_handle( 0, 0 ) ),
-        tail_( tagged_node_handle( 0, 0 ) ),
+#endif
         pool( alloc, capacity )
     {
         initialize();
@@ -219,10 +224,14 @@ class queue
      *
      *  \pre Must \b not specify a capacity<> argument
      * */
+#if !defined( BOOST_NO_CXX20_HDR_CONCEPTS )
+    explicit queue( size_type n )
+        requires( !has_capacity )
+        :
+#else
     template < typename Enabler = std::enable_if< !has_capacity > >
     explicit queue( size_type n ) :
-        head_( tagged_node_handle( 0, 0 ) ),
-        tail_( tagged_node_handle( 0, 0 ) ),
+#endif
         pool( node_allocator(), n + 1 )
     {
         initialize();
@@ -234,10 +243,13 @@ class queue
      *
      *  \pre Must \b not specify a capacity<> argument
      * */
+#if !defined( BOOST_NO_CXX20_HDR_CONCEPTS )
+    template < typename U >
+        requires( !has_capacity )
+#else
     template < typename U, typename Enabler = std::enable_if< !has_capacity > >
+#endif
     queue( size_type n, typename boost::allocator_rebind< node_allocator, U >::type const& alloc ) :
-        head_( tagged_node_handle( 0, 0 ) ),
-        tail_( tagged_node_handle( 0, 0 ) ),
         pool( alloc, n + 1 )
     {
         initialize();
@@ -249,10 +261,14 @@ class queue
      *
      *  \pre Must \b not specify a capacity<> argument
      * */
+#if !defined( BOOST_NO_CXX20_HDR_CONCEPTS )
+    queue( size_type n, allocator const& alloc )
+        requires( !has_capacity )
+        :
+#else
     template < typename Enabler = std::enable_if< !has_capacity > >
     queue( size_type n, allocator const& alloc ) :
-        head_( tagged_node_handle( 0, 0 ) ),
-        tail_( tagged_node_handle( 0, 0 ) ),
+#endif
         pool( alloc, n + 1 )
     {
         initialize();
@@ -625,8 +641,12 @@ class queue
 
 private:
 #ifndef BOOST_DOXYGEN_INVOKED
-    atomic< tagged_node_handle > head_;
-    alignas( detail::cacheline_bytes ) atomic< tagged_node_handle > tail_;
+    atomic< tagged_node_handle > head_ {
+        tagged_node_handle( 0, 0 ),
+    };
+    alignas( detail::cacheline_bytes ) atomic< tagged_node_handle > tail_ {
+        tagged_node_handle( 0, 0 ),
+    };
 
     pool_t pool;
 #endif

diff --git a/include/boost/lockfree/spsc_queue.hpp b/include/boost/lockfree/spsc_queue.hpp
@@ -43,13 +43,11 @@ class ringbuffer_base
 #ifndef BOOST_DOXYGEN_INVOKED
 protected:
     typedef std::size_t size_t;
-    alignas( cacheline_bytes ) atomic< size_t > write_index_;
-    alignas( cacheline_bytes ) atomic< size_t > read_index_;
+    alignas( cacheline_bytes ) atomic< size_t > write_index_ {};
+    alignas( cacheline_bytes ) atomic< size_t > read_index_ {};
 
 protected:
-    ringbuffer_base( void ) :
-        write_index_( 0 ),
-        read_index_( 0 )
+    ringbuffer_base( void )
     {}
 
     static size_t next_index( size_t arg, size_t max_size )
@@ -653,7 +651,12 @@ class spsc_queue : public detail::make_ringbuffer< T, Options... >::ringbuffer_t
      *
      *  \note This is just for API compatibility: an allocator isn't actually needed
      */
+#if !defined( BOOST_NO_CXX20_HDR_CONCEPTS )
+    template < typename U >
+        requires( !runtime_sized )
+#else
     template < typename U, typename Enabler = std::enable_if< !runtime_sized > >
+#endif
     explicit spsc_queue( typename boost::allocator_rebind< allocator, U >::type const& )
     {}
 
@@ -663,24 +666,40 @@ class spsc_queue : public detail::make_ringbuffer< T, Options... >::ringbuffer_t
      *
      *  \note This is just for API compatibility: an allocator isn't actually needed
      */
+#if !defined( BOOST_NO_CXX20_HDR_CONCEPTS )
+    explicit spsc_queue( allocator const& )
+        requires( !runtime_sized )
+#else
     template < typename Enabler = std::enable_if< !runtime_sized > >
     explicit spsc_queue( allocator const& )
+#endif
     {}
 
     /** Constructs a spsc_queue for element_count elements
      *
      *  \pre spsc_queue must be configured to be sized at run-time
      */
+#if !defined( BOOST_NO_CXX20_HDR_CONCEPTS )
+    explicit spsc_queue( size_type element_count )
+        requires( runtime_sized )
+#else
     template < typename Enabler = std::enable_if< runtime_sized > >
-    explicit spsc_queue( size_type element_count ) :
+    explicit spsc_queue( size_type element_count )
+#endif
+        :
         base_type( element_count )
     {}
 
     /** Constructs a spsc_queue for element_count elements with a custom allocator
      *
      *  \pre spsc_queue must be configured to be sized at run-time
      */
+#if !defined( BOOST_NO_CXX20_HDR_CONCEPTS )
+    template < typename U >
+        requires( runtime_sized )
+#else
     template < typename U, typename Enabler = std::enable_if< runtime_sized > >
+#endif
     spsc_queue( size_type element_count, typename boost::allocator_rebind< allocator, U >::type const& alloc ) :
         base_type( alloc, element_count )
     {}
@@ -689,8 +708,14 @@ class spsc_queue : public detail::make_ringbuffer< T, Options... >::ringbuffer_t
      *
      *  \pre spsc_queue must be configured to be sized at run-time
      */
+#if !defined( BOOST_NO_CXX20_HDR_CONCEPTS )
+    spsc_queue( size_type element_count, allocator_arg const& alloc )
+        requires( runtime_sized )
+#else
     template < typename Enabler = std::enable_if< runtime_sized > >
-    spsc_queue( size_type element_count, allocator_arg const& alloc ) :
+    spsc_queue( size_type element_count, allocator_arg const& alloc )
+#endif
+        :
         base_type( alloc, element_count )
     {}
 
@@ -739,7 +764,12 @@ class spsc_queue : public detail::make_ringbuffer< T, Options... >::ringbuffer_t
      *
      * \note Thread-safe and wait-free
      */
+#if !defined( BOOST_NO_CXX20_HDR_CONCEPTS )
+    template < typename U >
+        requires( std::is_convertible_v< T, U > )
+#else
     template < typename U, typename Enabler = std::enable_if< std::is_convertible< T, U >::value > >
+#endif
     bool pop( U& ret )
     {
         return consume_one( [ & ]( T&& t ) {
@@ -866,8 +896,16 @@ class spsc_queue : public detail::make_ringbuffer< T, Options... >::ringbuffer_t
      *
      * \note Thread-safe and wait-free
      * */
+#if !defined( BOOST_NO_CXX20_HDR_CONCEPTS )
     template < typename OutputIterator >
-    typename std::enable_if< !std::is_convertible< T, OutputIterator >::value, size_type >::type pop( OutputIterator it )
+        requires( !std::is_convertible_v< T, OutputIterator > )
+    size_type
+#else
+    template < typename OutputIterator,
+               typename Enabler = std::enable_if< !std::is_convertible< T, OutputIterator >::value > >
+    typename std::enable_if< !std::is_convertible< T, OutputIterator >::value, size_type >::type
+#endif
+    pop( OutputIterator it )
     {
         return base_type::pop_to_output_iterator( it );
     }