Adding upstream version 1.3+ds.upstream/1.3+dsupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 43 insertions, 0 deletions

diff --git a/src/display/initlock.h b/src/display/initlock.h
new file mode 100644
index 0000000..1a94069
--- /dev/null
+++ b/src/display/initlock.h
@@ -0,0 +1,43 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#ifndef INITLOCK_H
+#define INITLOCK_H
+
+#include <atomic>
+#include <mutex>
+
+/**
+ * Almost entirely analogous to std::once_flag, but with the ability to be reset if the caller knows it is safe to do so.
+ */
+class InitLock
+{
+public:
+    template <typename F>
+    void init(F &&f) const
+    {
+        // Make sure the fast path is a single load-acquire - not guaranteed with std::once_flag.
+        [[likely]] if (inited.load(std::memory_order_acquire)) {
+            return;
+        }
+
+        std::call_once(once, [&] {
+            f();
+            inited.store(true, std::memory_order_release);
+        });
+    }
+
+    void reset()
+    {
+        inited.store(false, std::memory_order_relaxed);
+
+        // Abomination, but tenuously allowed by Standard.
+        // (The alternative, std::mutex, is too large - we want to create a lot of these objects.)
+        once.~once_flag();
+        new (&once) std::once_flag();
+    }
+
+private:
+    mutable std::once_flag once;
+    mutable std::atomic<bool> inited = false;
+};
+
+#endif // INITLOCK_H