1 files changed, 50 insertions, 0 deletions
diff --git a/contrib/libc++/src/memory.cpp b/contrib/libc++/src/memory.cpp
index a892e75c86d0..3884a2b3abf8 100644
--- a/contrib/libc++/src/memory.cpp
+++ b/contrib/libc++/src/memory.cpp
@@ -7,7 +7,10 @@
 //
 //===----------------------------------------------------------------------===//
 
+#define _LIBCPP_BUILDING_MEMORY
 #include "memory"
+#include "mutex"
+#include "thread"
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
@@ -116,6 +119,53 @@ __shared_weak_count::__get_deleter(const type_info&) const _NOEXCEPT
 
 #endif  // _LIBCPP_NO_RTTI
 
+#if __has_feature(cxx_atomic)
+
+static const std::size_t __sp_mut_count = 16;
+static mutex mut_back[__sp_mut_count];
+
+_LIBCPP_CONSTEXPR __sp_mut::__sp_mut(void* p) _NOEXCEPT
+   : _(p)
+{
+}
+
+void
+__sp_mut::lock() _NOEXCEPT
+{
+    mutex& m = *static_cast<mutex*>(_);
+    unsigned count = 0;
+    while (!m.try_lock())
+    {
+        if (++count > 16)
+        {
+            m.lock();
+            break;
+        }
+        this_thread::yield();
+    }
+}
+
+void
+__sp_mut::unlock() _NOEXCEPT
+{
+    static_cast<mutex*>(_)->unlock();
+}
+
+__sp_mut&
+__get_sp_mut(const void* p)
+{
+    static __sp_mut muts[__sp_mut_count] 
+    {
+        &mut_back[ 0], &mut_back[ 1], &mut_back[ 2], &mut_back[ 3],
+        &mut_back[ 4], &mut_back[ 5], &mut_back[ 6], &mut_back[ 7],
+        &mut_back[ 8], &mut_back[ 9], &mut_back[10], &mut_back[11],
+        &mut_back[12], &mut_back[13], &mut_back[14], &mut_back[15]
+    };
+    return muts[hash<const void*>()(p) & (__sp_mut_count-1)];
+}
+
+#endif // __has_feature(cxx_atomic)
+
 void
 declare_reachable(void*)
 {