[util] Add ticket lock implementation

src/util/sync/sync_ticketlock.h

@@ -0,0 +1,39 @@
+#pragma once
+
+#include <atomic>
+
+#include "../thread.h"
+
+namespace dxvk::sync {
+  
+  /**
+   * \brief Ticket spinlock
+   * 
+   * A fair spinlock implementation that should
+   * be preferred over \ref Spinlock when one of
+   * the threads accessing the lock is likely to
+   * starve another.
+   */
+  class TicketLock {
+
+  public:
+
+    void lock() {
+      uint32_t ticket = m_counter.fetch_add(1);
+
+      while (m_serving.load(std::memory_order_acquire) != ticket)
+        continue;
+    }
+
+    void unlock() {
+      m_serving.fetch_add(1, std::memory_order_release);
+    }
+
+  private:
+
+    std::atomic<uint32_t> m_counter = { 0 };
+    std::atomic<uint32_t> m_serving = { 0 };
+
+  };
+  
+}