1 files changed, 62 insertions, 0 deletions
diff --git a/lib/windows-once.c b/lib/windows-once.c
new file mode 100644
index 0000000..c431bd6
--- /dev/null
+++ b/lib/windows-once.c
@@ -0,0 +1,62 @@
+/* Once-only control (native Windows implementation).
+   Copyright (C) 2005-2020 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3, or (at your option)
+   any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, see <https://www.gnu.org/licenses/>.  */
+
+/* Written by Bruno Haible <bruno@clisp.org>, 2005.
+   Based on GCC's gthr-win32.h.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include "windows-once.h"
+
+#include <stdlib.h>
+
+void
+glwthread_once (glwthread_once_t *once_control, void (*initfunction) (void))
+{
+  if (once_control->inited <= 0)
+    {
+      if (InterlockedIncrement (&once_control->started) == 0)
+        {
+          /* This thread is the first one to come to this once_control.  */
+          InitializeCriticalSection (&once_control->lock);
+          EnterCriticalSection (&once_control->lock);
+          once_control->inited = 0;
+          initfunction ();
+          once_control->inited = 1;
+          LeaveCriticalSection (&once_control->lock);
+        }
+      else
+        {
+          /* Don't let once_control->started grow and wrap around.  */
+          InterlockedDecrement (&once_control->started);
+          /* Some other thread has already started the initialization.
+             Yield the CPU while waiting for the other thread to finish
+             initializing and taking the lock.  */
+          while (once_control->inited < 0)
+            Sleep (0);
+          if (once_control->inited <= 0)
+            {
+              /* Take the lock.  This blocks until the other thread has
+                 finished calling the initfunction.  */
+              EnterCriticalSection (&once_control->lock);
+              LeaveCriticalSection (&once_control->lock);
+              if (!(once_control->inited > 0))
+                abort ();
+            }
+        }
+    }
+}