Made the mem_cache_block lockfree

include/boost/regex/v4/mem_block_cache.hpp

@@ -27,9 +27,54 @@
 #  include BOOST_ABI_PREFIX
 #endif
 
+#ifndef BOOST_NO_CXX11_HDR_ATOMIC
+  #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
+{
+  std::atomic<void*> cache[BOOST_REGEX_MAX_CACHE_BLOCKS];
+
+   ~mem_block_cache()
+   {
+     for (size_t i = 0;i < BOOST_REGEX_MAX_CACHE_BLOCKS; ++i) {
+       if (cache[i].load()) ::operator delete(cache[i].load());
+     }
+   }
+   void* get()
+   {
+     for (size_t i = 0;i < BOOST_REGEX_MAX_CACHE_BLOCKS; ++i) {
+       void* p = cache[i].load();
+       if (p != NULL) {
+         if (cache[i].compare_exchange_strong(p, NULL)) return p;
+       }
+     }
+     return ::operator new(BOOST_REGEX_BLOCKSIZE);
+   }
+   void put(void* ptr)
+   {
+     for (size_t i = 0;i < BOOST_REGEX_MAX_CACHE_BLOCKS; ++i) {
+       void* p = cache[i].load();
+       if (p == NULL) {
+         if (cache[i].compare_exchange_strong(p, ptr)) return;
+       }
+     }
+     ::operator delete(ptr);
+   }
+};
+
+
+#else /* lock-based implementation */
+
+
 struct mem_block_node
 {
    mem_block_node* next;
@@ -85,6 +130,7 @@ struct mem_block_cache
       }
    }
 };
+#endif
 
 extern mem_block_cache block_cache;
 

src/regex.cpp

@@ -191,7 +191,9 @@ BOOST_REGEX_DECL void BOOST_REGEX_CALL put_mem_block(void* p)
 
 #else
 
-#ifdef BOOST_HAS_THREADS
+#if defined(BOOST_REGEX_MEM_BLOCK_CACHE_LOCK_FREE)
+mem_block_cache block_cache = { { {nullptr} } } ;
+#elif defined(BOOST_HAS_THREADS)
 mem_block_cache block_cache = { 0, 0, BOOST_STATIC_MUTEX_INIT, };
 #else
 mem_block_cache block_cache = { 0, 0, };