1 files changed, 62 insertions, 7 deletions

diff --git a/core/os/mutex.h b/core/os/mutex.h
index ceedcb235a..90cc1632e8 100644
--- a/core/os/mutex.h
+++ b/core/os/mutex.h
@@ -31,12 +31,20 @@
 #ifndef MUTEX_H
 #define MUTEX_H
 
+#include "core/error/error_macros.h"
 #include "core/typedefs.h"
 
 #include <mutex>
 
+template <class MutexT>
+class MutexLock;
+
 template <class StdMutexT>
 class MutexImpl {
+	friend class MutexLock<MutexImpl<StdMutexT>>;
+
+	using StdMutexType = StdMutexT;
+
 	mutable StdMutexT mutex;
 
 public:
@@ -53,18 +61,65 @@ public:
 	}
 };
 
+// A very special kind of mutex, used in scenarios where these
+// requirements hold at the same time:
+// - Must be used with a condition variable (only binary mutexes are suitable).
+// - Must have recursive semnantics (or simulate, as this one does).
+// The implementation keeps the lock count in TS. Therefore, only
+// one object of each version of the template can exists; hence the Tag argument.
+// Tags must be unique across the Godot codebase.
+// Also, don't forget to declare the thread_local variable on each use.
+template <int Tag>
+class SafeBinaryMutex {
+	friend class MutexLock<SafeBinaryMutex>;
+
+	using StdMutexType = std::mutex;
+
+	mutable std::mutex mutex;
+	static thread_local uint32_t count;
+
+public:
+	_ALWAYS_INLINE_ void lock() const {
+		if (++count == 1) {
+			mutex.lock();
+		}
+	}
+
+	_ALWAYS_INLINE_ void unlock() const {
+		DEV_ASSERT(count);
+		if (--count == 0) {
+			mutex.unlock();
+		}
+	}
+
+	_ALWAYS_INLINE_ bool try_lock() const {
+		if (count) {
+			count++;
+			return true;
+		} else {
+			if (mutex.try_lock()) {
+				count++;
+				return true;
+			} else {
+				return false;
+			}
+		}
+	}
+
+	~SafeBinaryMutex() {
+		DEV_ASSERT(!count);
+	}
+};
+
 template <class MutexT>
 class MutexLock {
-	const MutexT &mutex;
+	friend class ConditionVariable;
+
+	std::unique_lock<typename MutexT::StdMutexType> lock;
 
 public:
 	_ALWAYS_INLINE_ explicit MutexLock(const MutexT &p_mutex) :
-			mutex(p_mutex) {
-		mutex.lock();
-	}
-
-	_ALWAYS_INLINE_ ~MutexLock() {
-		mutex.unlock();
+			lock(p_mutex.mutex) {
 	}
 };