1 files changed, 19 insertions, 0 deletions
diff --git a/llvm/lib/Support/Windows/Threading.inc b/llvm/lib/Support/Windows/Threading.inc
new file mode 100644
index 00000000000..099c6b28bf6
--- /dev/null
+++ b/llvm/lib/Support/Windows/Threading.inc
@@ -0,0 +1,19 @@
+#include <winbase.h>
+
+void llvm::call_once(once_flag &flag, void (*fptr)(void)) {
+  while (flag != Done) {
+    if (flag == Wait) {
+      ::Sleep(1);
+      continue;
+    }
+
+    sys::cas_flag old_val = sys::CompareAndSwap(&flag, Wait, Uninitialized);
+    if (old_val == Uninitialized) {
+      fptr();
+      sys::MemoryFence();
+      flag = Done;
+      return;
+    }
+  }
+  sys::MemoryFence();
+}