Implement ConditionVariable

2 files changed, 122 insertions, 7 deletions

diff --git a/core/os/condition_variable.h b/core/os/condition_variable.h
new file mode 100644
index 0000000000..6037ff327d
--- /dev/null
+++ b/core/os/condition_variable.h
@@ -0,0 +1,60 @@
+/**************************************************************************/
+/*  condition_variable.h                                                  */
+/**************************************************************************/
+/*                         This file is part of:                          */
+/*                             GODOT ENGINE                               */
+/*                        https://godotengine.org                         */
+/**************************************************************************/
+/* Copyright (c) 2014-present Godot Engine contributors (see AUTHORS.md). */
+/* Copyright (c) 2007-2014 Juan Linietsky, Ariel Manzur.                  */
+/*                                                                        */
+/* Permission is hereby granted, free of charge, to any person obtaining  */
+/* a copy of this software and associated documentation files (the        */
+/* "Software"), to deal in the Software without restriction, including    */
+/* without limitation the rights to use, copy, modify, merge, publish,    */
+/* distribute, sublicense, and/or sell copies of the Software, and to     */
+/* permit persons to whom the Software is furnished to do so, subject to  */
+/* the following conditions:                                              */
+/*                                                                        */
+/* The above copyright notice and this permission notice shall be         */
+/* included in all copies or substantial portions of the Software.        */
+/*                                                                        */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,        */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF     */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. */
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY   */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,   */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE      */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                 */
+/**************************************************************************/
+
+#ifndef CONDITION_VARIABLE_H
+#define CONDITION_VARIABLE_H
+
+#include <condition_variable>
+
+// An object one or multiple threads can wait on a be notified by some other.
+// Normally, you want to use a semaphore for such scenarios, but when the
+// condition is something different than a count being greater than zero
+// (which is the built-in logic in a semaphore) or you want to provide your
+// own mutex to tie the wait-notify to some other behavior, you need to use this.
+
+class ConditionVariable {
+	mutable std::condition_variable condition;
+
+public:
+	template <class BinaryMutexT>
+	_ALWAYS_INLINE_ void wait(const MutexLock<BinaryMutexT> &p_lock) const {
+		condition.wait(const_cast<std::unique_lock<std::mutex> &>(p_lock.lock));
+	}
+
+	_ALWAYS_INLINE_ void notify_one() const {
+		condition.notify_one();
+	}
+
+	_ALWAYS_INLINE_ void notify_all() const {
+		condition.notify_all();
+	}
+};
+
+#endif // CONDITION_VARIABLE_H
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) {
 	}
 };