Updated with platform checks

include/boost/regex/v4/mem_block_cache.hpp

@@ -25,12 +25,26 @@
 #  include BOOST_ABI_PREFIX
 #endif
 
+#ifdef BOOST_NO_CXX11_HDR_ATOMIC
+  #if BOOST_ATOMIC_POINTER_LOCK_FREE == 2
+    #define BOOST_REGEX_MEM_BLOCK_CACHE_LOCK_FREE
+    #define BOOST_REGEX_ATOMIC_POINTER boost::atomic
+  #endif
+#else // BOOST_NOCXX11_HDR_ATOMIC not defined
+  #include <atomic>
+  #if ATOMIC_POINTER_LOCK_FREE == 2
+    #define BOOST_REGEX_MEM_BLOCK_CACHE_LOCK_FREE
+    #define BOOST_REGEX_ATOMIC_POINTER std::atomic
+  #endif
+#endif
+
 namespace boost{
 namespace BOOST_REGEX_DETAIL_NS{
 
+#ifdef BOOST_REGEX_MEM_BLOCK_CACHE_LOCK_FREE /* lock free implementation */
 struct mem_block_cache
 {
-   boost::atomic<void*> cache[BOOST_REGEX_MAX_CACHE_BLOCKS];
+   BOOST_REGEX_ATOMIC_POINTER<void*> cache[BOOST_REGEX_MAX_CACHE_BLOCKS];
 
    mem_block_cache() {
      for (size_t i = 0;i < BOOST_REGEX_MAX_CACHE_BLOCKS; ++i) {
@@ -66,6 +80,68 @@ struct mem_block_cache
    }
 };
 
+#undef BOOST_REGEX_ATOMIC_POINTER
+
+#else /* lock-based implementation */
+
+
+struct mem_block_node
+{
+   mem_block_node* next;
+};
+
+struct mem_block_cache
+{
+   // this member has to be statically initialsed:
+   mem_block_node* next;
+   unsigned cached_blocks;
+#ifdef BOOST_HAS_THREADS
+   boost::static_mutex mut;
+#endif
+
+   ~mem_block_cache()
+   {
+      while(next)
+      {
+         mem_block_node* old = next;
+         next = next->next;
+         ::operator delete(old);
+      }
+   }
+   void* get()
+   {
+#ifdef BOOST_HAS_THREADS
+      boost::static_mutex::scoped_lock g(mut);
+#endif
+     if(next)
+      {
+         mem_block_node* result = next;
+         next = next->next;
+         --cached_blocks;
+         return result;
+      }
+      return ::operator new(BOOST_REGEX_BLOCKSIZE);
+   }
+   void put(void* p)
+   {
+#ifdef BOOST_HAS_THREADS
+      boost::static_mutex::scoped_lock g(mut);
+#endif
+      if(cached_blocks >= BOOST_REGEX_MAX_CACHE_BLOCKS)
+      {
+         ::operator delete(p);
+      }
+      else
+      {
+         mem_block_node* old = static_cast<mem_block_node*>(p);
+         old->next = next;
+         next = old;
+         ++cached_blocks;
+      }
+   }
+};
+#endif
+
 extern mem_block_cache block_cache;
 
 }