swift_once implemented

Author: tinysun212

include/swift/Runtime/Once.h

@@ -27,6 +27,11 @@ namespace swift {
 // On OS X and iOS, swift_once_t matches dispatch_once_t.
 typedef long swift_once_t;
 
+#elif defined(__CYGWIN__)
+
+// On Cygwin, std::once_flag can not be used because it is larger than the
+// platform word.
+typedef unsigned long swift_once_t;
 #else
 
 // On other platforms swift_once_t is std::once_flag

stdlib/public/runtime/Once.cpp

@@ -17,6 +17,9 @@
 #include "swift/Runtime/Once.h"
 #include "swift/Runtime/Debug.h"
 #include <type_traits>
+#if defined(__CYGWIN__)
+#include <mutex>
+#endif
 
 using namespace swift;
 
@@ -31,9 +34,11 @@ static_assert(std::is_same<swift_once_t, dispatch_once_t>::value,
 // The compiler generates the swift_once_t values as word-sized zero-initialized
 // variables, so we want to make sure swift_once_t isn't larger than the
 // platform word or the function below might overwrite something it shouldn't.
-#if !defined(__CYGWIN__)
 static_assert(sizeof(swift_once_t) <= sizeof(void*),
               "swift_once_t must be no larger than the platform word");
+
+#if defined(__CYGWIN__)
+static std::mutex mutex_;
 #endif
 
 /// Runs the given function with the given context argument exactly once.
@@ -42,6 +47,18 @@ static_assert(sizeof(swift_once_t) <= sizeof(void*),
 void swift::swift_once(swift_once_t *predicate, void (*fn)(void *)) {
 #if defined(__APPLE__)
   dispatch_once_f(predicate, nullptr, fn);
+#else
+#if defined(__CYGWIN__)
+
+  mutex_.lock();
+  if (*predicate == 0) {
+    *predicate = 1ul;
+    mutex_.unlock();
+
+    fn(nullptr);
+  } else
+    mutex_.unlock();
+
 #else
   // FIXME: We're relying here on the coincidence that libstdc++ uses pthread's
   // pthread_once, and that on glibc pthread_once follows a compatible init
@@ -51,4 +68,5 @@ void swift::swift_once(swift_once_t *predicate, void (*fn)(void *)) {
   // For more information, see rdar://problem/18499385
   std::call_once(*predicate, [fn]() { fn(nullptr); });
 #endif
+#endif
 }