Implement util/fifo_mutex.hpp

Prototype. Uses 2 bytes.
Added minor fix to slow_mutex.hpp as well.

rpcs3/emucore.vcxproj

@@ -498,6 +498,8 @@
     <ClInclude Include="util\fixed_typemap.hpp" />
     <ClInclude Include="util\auto_typemap.hpp" />
     <ClInclude Include="util\init_mutex.hpp" />
+    <ClInclude Include="util\slow_mutex.hpp" />
+    <ClInclude Include="util\fifo_mutex.hpp" />
     <ClInclude Include="util\logs.hpp" />
     <ClInclude Include="..\Utilities\dyn_lib.hpp" />
     <ClInclude Include="..\Utilities\File.h" />

rpcs3/emucore.vcxproj.filters

@@ -1831,6 +1831,12 @@
     <ClInclude Include="util\init_mutex.hpp">
       <Filter>Utilities</Filter>
     </ClInclude>
+    <ClInclude Include="util\slow_mutex.hpp">
+      <Filter>Utilities</Filter>
+    </ClInclude>
+    <ClInclude Include="util\fifo_mutex.hpp">
+      <Filter>Utilities</Filter>
+    </ClInclude>
     <ClInclude Include="util\logs.hpp">
       <Filter>Utilities</Filter>
     </ClInclude>

rpcs3/util/fifo_mutex.hpp

@@ -0,0 +1,70 @@
+#pragma once
+
+#include "util/types.hpp"
+#include "util/atomic.hpp"
+#include <mutex>
+
+// Mutex that tries to maintain the order of acquisition
+class fifo_mutex
+{
+	// Low 8 bits are incremented on acquisition, high 8 bits are incremented on release
+	atomic_t<u16> m_value{0};
+
+public:
+	constexpr fifo_mutex() noexcept = default;
+
+	void lock() noexcept
+	{
+		const u16 val = m_value.fetch_op([](u16& val)
+		{
+			val = (val & 0xff00) | ((val + 1) & 0xff);
+		});
+
+		if (val >> 8 != (val & 0xff)) [[unlikely]]
+		{
+			// TODO: implement busy waiting along with moving to cpp file
+			m_value.wait<atomic_wait::op_ne>(((val + 1) & 0xff) << 8, 0xff00);
+		}
+	}
+
+	bool try_lock() noexcept
+	{
+		const u16 val = m_value.load();
+
+		if (val >> 8 == (val & 0xff))
+		{
+			if (m_value.compare_and_swap(val, ((val + 1) & 0xff) | (val & 0xff00)))
+			{
+				return true;
+			}
+		}
+
+		return false;
+	}
+
+	void unlock() noexcept
+	{
+		const u16 val = m_value.add_fetch(0x100);
+
+		if (val >> 8 != (val & 0xff))
+		{
+			m_value.notify_one();
+		}
+	}
+
+	bool is_free() const noexcept
+	{
+		const u16 val = m_value.load();
+
+		return (val >> 8) == (val & 0xff);
+	}
+
+	void lock_unlock() noexcept
+	{
+		if (!is_free())
+		{
+			lock();
+			unlock();
+		}
+	}
+};

rpcs3/util/slow_mutex.hpp

@@ -1,6 +1,7 @@
 #pragma once
 
-#include "atomic.hpp"
+#include "util/types.hpp"
+#include "util/atomic.hpp"
 #include "Utilities/StrFmt.h"
 #include <mutex>
 
@@ -79,7 +80,7 @@ public:
 		}
 	}
 
-	bool is_free() noexcept
+	bool is_free() const noexcept
 	{
 		return !m_value;
 	}