Extract 'SafeBinaryMutex' to separate header

    This change simply extracts 'SafeBinaryMutex' from 'mutex.h' to
    'safe_binary_mutex.h', in an effort to reduce the compilation
    speed impact of including `mutex.h`.

1 files changed, 124 insertions, 0 deletions

diff --git a/core/os/safe_binary_mutex.h b/core/os/safe_binary_mutex.h
new file mode 100644
index 0000000000..1e98cc074c
--- /dev/null
+++ b/core/os/safe_binary_mutex.h
@@ -0,0 +1,124 @@
+/**************************************************************************/
+/*  safe_binary_mutex.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 SAFE_BINARY_MUTEX_H
+#define SAFE_BINARY_MUTEX_H
+
+#include "core/error/error_macros.h"
+#include "core/os/mutex.h"
+#include "core/typedefs.h"
+
+#ifdef THREADS_ENABLED
+
+// 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 = THREADING_NAMESPACE::mutex;
+
+	mutable THREADING_NAMESPACE::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);
+	}
+};
+
+// This specialization is needed so manual locking and MutexLock can be used
+// at the same time on a SafeBinaryMutex.
+template <int Tag>
+class MutexLock<SafeBinaryMutex<Tag>> {
+	friend class ConditionVariable;
+
+	THREADING_NAMESPACE::unique_lock<THREADING_NAMESPACE::mutex> lock;
+
+public:
+	_ALWAYS_INLINE_ explicit MutexLock(const SafeBinaryMutex<Tag> &p_mutex) :
+			lock(p_mutex.mutex) {
+		SafeBinaryMutex<Tag>::count++;
+	};
+	_ALWAYS_INLINE_ ~MutexLock() {
+		SafeBinaryMutex<Tag>::count--;
+	};
+};
+
+#else // No threads.
+
+template <int Tag>
+class SafeBinaryMutex : public MutexImpl {
+	static thread_local uint32_t count;
+};
+
+template <int Tag>
+class MutexLock<SafeBinaryMutex<Tag>> {
+public:
+	MutexLock(const SafeBinaryMutex<Tag> &p_mutex) {}
+	~MutexLock() {}
+};
+
+#endif // THREADS_ENABLED
+
+#endif // SAFE_BINARY_MUTEX_H