Reimplement Mutex with C++'s <mutex>

Main:
- It's now implemented thanks to `<mutex>`. No more platform-specific implementations.
- `BinaryMutex` (non-recursive) is added, as an alternative for special cases.
- Doesn't need allocation/deallocation anymore. It can live in the stack and be part of other classes.
- Because of that, it's methods are now `const` and the inner mutex is `mutable` so it can be easily used in `const` contexts.
- A no-op implementation is provided if `NO_THREADS` is defined. No more need to add `#ifdef NO_THREADS` just for this.
- `MutexLock` now takes a reference. At this point the cases of null `Mutex`es are rare. If you ever need that, just don't use `MutexLock`.
- Thread-safe utilities are therefore simpler now.

Misc.:
- `ScopedMutexLock` is dropped and replaced by `MutexLock`, because they were pretty much the same.
- Every case of lock, do-something, unlock is replaced by `MutexLock` (complex cases where it's not straightfoward are kept as as explicit lock and unlock).
- `ShaderRD` contained an `std::mutex`, which has been replaced by `Mutex`.

4 files changed, 22 insertions, 130 deletions

diff --git a/modules/mono/csharp_script.cpp b/modules/mono/csharp_script.cpp
index 5c1c098e3e..404d2eb022 100644
--- a/modules/mono/csharp_script.cpp
+++ b/modules/mono/csharp_script.cpp
@@ -35,6 +35,7 @@
 
 #include "core/io/json.h"
 #include "core/os/file_access.h"
+#include "core/os/mutex.h"
 #include "core/os/os.h"
 #include "core/os/thread.h"
 #include "core/project_settings.h"
@@ -58,7 +59,6 @@
 #include "mono_gd/gd_mono_utils.h"
 #include "signal_awaiter_utils.h"
 #include "utils/macros.h"
-#include "utils/mutex_utils.h"
 #include "utils/string_utils.h"
 #include "utils/thread_local.h"
 
@@ -633,7 +633,7 @@ Vector<ScriptLanguage::StackInfo> CSharpLanguage::stack_trace_get_info(MonoObjec
 
 void CSharpLanguage::post_unsafe_reference(Object *p_obj) {
 #ifdef DEBUG_ENABLED
-	SCOPED_MUTEX_LOCK(unsafe_object_references_lock);
+	MutexLock lock(unsafe_object_references_lock);
 	ObjectID id = p_obj->get_instance_id();
 	unsafe_object_references[id]++;
 #endif
@@ -641,7 +641,7 @@ void CSharpLanguage::post_unsafe_reference(Object *p_obj) {
 
 void CSharpLanguage::pre_unsafe_unreference(Object *p_obj) {
 #ifdef DEBUG_ENABLED
-	SCOPED_MUTEX_LOCK(unsafe_object_references_lock);
+	MutexLock lock(unsafe_object_references_lock);
 	ObjectID id = p_obj->get_instance_id();
 	Map<ObjectID, int>::Element *elem = unsafe_object_references.find(id);
 	ERR_FAIL_NULL(elem);
@@ -764,7 +764,7 @@ void CSharpLanguage::reload_assemblies(bool p_soft_reload) {
 	List<Ref<CSharpScript> > scripts;
 
 	{
-		SCOPED_MUTEX_LOCK(script_instances_mutex);
+		MutexLock lock(script_instances_mutex);
 
 		for (SelfList<CSharpScript> *elem = script_list.first(); elem; elem = elem->next()) {
 			// Cast to CSharpScript to avoid being erased by accident
@@ -1204,7 +1204,7 @@ void CSharpLanguage::set_language_index(int p_idx) {
 void CSharpLanguage::release_script_gchandle(Ref<MonoGCHandle> &p_gchandle) {
 
 	if (!p_gchandle->is_released()) { // Do not lock unnecessarily
-		SCOPED_MUTEX_LOCK(get_singleton()->script_gchandle_release_mutex);
+		MutexLock lock(get_singleton()->script_gchandle_release_mutex);
 		p_gchandle->release();
 	}
 }
@@ -1214,7 +1214,7 @@ void CSharpLanguage::release_script_gchandle(MonoObject *p_expected_obj, Ref<Mon
 	uint32_t pinned_gchandle = MonoGCHandle::new_strong_handle_pinned(p_expected_obj); // We might lock after this, so pin it
 
 	if (!p_gchandle->is_released()) { // Do not lock unnecessarily
-		SCOPED_MUTEX_LOCK(get_singleton()->script_gchandle_release_mutex);
+		MutexLock lock(get_singleton()->script_gchandle_release_mutex);
 
 		MonoObject *target = p_gchandle->get_target();
 
@@ -1239,24 +1239,6 @@ CSharpLanguage::CSharpLanguage() {
 
 	gdmono = NULL;
 
-#ifdef NO_THREADS
-	script_instances_mutex = NULL;
-	script_gchandle_release_mutex = NULL;
-	language_bind_mutex = NULL;
-#else
-	script_instances_mutex = Mutex::create();
-	script_gchandle_release_mutex = Mutex::create();
-	language_bind_mutex = Mutex::create();
-#endif
-
-#ifdef DEBUG_ENABLED
-#ifdef NO_THREADS
-	unsafe_object_references_lock = NULL;
-#else
-	unsafe_object_references_lock = Mutex::create();
-#endif
-#endif
-
 	lang_idx = -1;
 
 	scripts_metadata_invalidated = true;
@@ -1269,29 +1251,6 @@ CSharpLanguage::CSharpLanguage() {
 CSharpLanguage::~CSharpLanguage() {
 
 	finish();
-
-	if (script_instances_mutex) {
-		memdelete(script_instances_mutex);
-		script_instances_mutex = NULL;
-	}
-
-	if (language_bind_mutex) {
-		memdelete(language_bind_mutex);
-		language_bind_mutex = NULL;
-	}
-
-	if (script_gchandle_release_mutex) {
-		memdelete(script_gchandle_release_mutex);
-		script_gchandle_release_mutex = NULL;
-	}
-
-#ifdef DEBUG_ENABLED
-	if (unsafe_object_references_lock) {
-		memdelete(unsafe_object_references_lock);
-		unsafe_object_references_lock = NULL;
-	}
-#endif
-
 	singleton = NULL;
 }
 
@@ -1346,7 +1305,7 @@ bool CSharpLanguage::setup_csharp_script_binding(CSharpScriptBinding &r_script_b
 
 void *CSharpLanguage::alloc_instance_binding_data(Object *p_object) {
 
-	SCOPED_MUTEX_LOCK(language_bind_mutex);
+	MutexLock lock(language_bind_mutex);
 
 	Map<Object *, CSharpScriptBinding>::Element *match = script_bindings.find(p_object);
 	if (match)
@@ -1381,7 +1340,7 @@ void CSharpLanguage::free_instance_binding_data(void *p_data) {
 	GD_MONO_ASSERT_THREAD_ATTACHED;
 
 	{
-		SCOPED_MUTEX_LOCK(language_bind_mutex);
+		MutexLock lock(language_bind_mutex);
 
 		Map<Object *, CSharpScriptBinding>::Element *data = (Map<Object *, CSharpScriptBinding>::Element *)p_data;
 
@@ -2187,7 +2146,7 @@ CSharpInstance::~CSharpInstance() {
 		CSharpScriptBinding &script_binding = ((Map<Object *, CSharpScriptBinding>::Element *)data)->get();
 
 		if (!script_binding.inited) {
-			SCOPED_MUTEX_LOCK(CSharpLanguage::get_singleton()->get_language_bind_mutex());
+			MutexLock lock(CSharpLanguage::get_singleton()->get_language_bind_mutex());
 
 			if (!script_binding.inited) { // Other thread may have set it up
 				// Already had a binding that needs to be setup
@@ -2203,7 +2162,7 @@ CSharpInstance::~CSharpInstance() {
 	}
 
 	if (script.is_valid() && owner) {
-		SCOPED_MUTEX_LOCK(CSharpLanguage::get_singleton()->script_instances_mutex);
+		MutexLock lock(CSharpLanguage::get_singleton()->script_instances_mutex);
 
 #ifdef DEBUG_ENABLED
 		// CSharpInstance must not be created unless it's going to be added to the list for sure
@@ -2979,7 +2938,7 @@ CSharpInstance *CSharpScript::_create_instance(const Variant **p_args, int p_arg
 		instance->_reference_owner_unsafe(); // Here, after assigning the gchandle (for the refcount_incremented callback)
 
 	{
-		SCOPED_MUTEX_LOCK(CSharpLanguage::get_singleton()->script_instances_mutex);
+		MutexLock lock(CSharpLanguage::get_singleton()->script_instances_mutex);
 		instances.insert(instance->owner);
 	}
 
@@ -3067,7 +3026,7 @@ PlaceHolderScriptInstance *CSharpScript::placeholder_instance_create(Object *p_t
 
 bool CSharpScript::instance_has(const Object *p_this) const {
 
-	SCOPED_MUTEX_LOCK(CSharpLanguage::get_singleton()->script_instances_mutex);
+	MutexLock lock(CSharpLanguage::get_singleton()->script_instances_mutex);
 	return instances.has((Object *)p_this);
 }
 
@@ -3140,7 +3099,7 @@ Error CSharpScript::reload(bool p_keep_state) {
 
 	bool has_instances;
 	{
-		SCOPED_MUTEX_LOCK(CSharpLanguage::get_singleton()->script_instances_mutex);
+		MutexLock lock(CSharpLanguage::get_singleton()->script_instances_mutex);
 		has_instances = instances.size();
 	}
 
@@ -3476,7 +3435,7 @@ CSharpScript::CSharpScript() :
 
 #ifdef DEBUG_ENABLED
 	{
-		SCOPED_MUTEX_LOCK(CSharpLanguage::get_singleton()->script_instances_mutex);
+		MutexLock lock(CSharpLanguage::get_singleton()->script_instances_mutex);
 		CSharpLanguage::get_singleton()->script_list.add(&this->script_list);
 	}
 #endif
@@ -3485,7 +3444,7 @@ CSharpScript::CSharpScript() :
 CSharpScript::~CSharpScript() {
 
 #ifdef DEBUG_ENABLED
-	SCOPED_MUTEX_LOCK(CSharpLanguage::get_singleton()->script_instances_mutex);
+	MutexLock lock(CSharpLanguage::get_singleton()->script_instances_mutex);
 	CSharpLanguage::get_singleton()->script_list.remove(&this->script_list);
 #endif
 }
diff --git a/modules/mono/csharp_script.h b/modules/mono/csharp_script.h
index 627218eaf5..f44c4aebc4 100644
--- a/modules/mono/csharp_script.h
+++ b/modules/mono/csharp_script.h
@@ -325,16 +325,16 @@ class CSharpLanguage : public ScriptLanguage {
 	GDMono *gdmono;
 	SelfList<CSharpScript>::List script_list;
 
-	Mutex *script_instances_mutex;
-	Mutex *script_gchandle_release_mutex;
-	Mutex *language_bind_mutex;
+	Mutex script_instances_mutex;
+	Mutex script_gchandle_release_mutex;
+	Mutex language_bind_mutex;
 
 	Map<Object *, CSharpScriptBinding> script_bindings;
 
 #ifdef DEBUG_ENABLED
 	// List of unsafe object references
 	Map<ObjectID, int> unsafe_object_references;
-	Mutex *unsafe_object_references_lock;
+	Mutex unsafe_object_references_lock;
 #endif
 
 	struct StringNameCache {
@@ -376,7 +376,7 @@ class CSharpLanguage : public ScriptLanguage {
 public:
 	StringNameCache string_names;
 
-	Mutex *get_language_bind_mutex() { return language_bind_mutex; }
+	const Mutex &get_language_bind_mutex() { return language_bind_mutex; }
 
 	_FORCE_INLINE_ int get_language_index() { return lang_idx; }
 	void set_language_index(int p_idx);
diff --git a/modules/mono/mono_gd/gd_mono_utils.cpp b/modules/mono/mono_gd/gd_mono_utils.cpp
index ae6625a6c6..41f49d8ac9 100644
--- a/modules/mono/mono_gd/gd_mono_utils.cpp
+++ b/modules/mono/mono_gd/gd_mono_utils.cpp
@@ -33,6 +33,7 @@
 #include <mono/metadata/exception.h>
 
 #include "core/os/dir_access.h"
+#include "core/os/mutex.h"
 #include "core/os/os.h"
 #include "core/project_settings.h"
 #include "core/reference.h"
@@ -43,7 +44,6 @@
 
 #include "../csharp_script.h"
 #include "../utils/macros.h"
-#include "../utils/mutex_utils.h"
 #include "gd_mono.h"
 #include "gd_mono_cache.h"
 #include "gd_mono_class.h"
@@ -74,7 +74,7 @@ MonoObject *unmanaged_get_managed(Object *unmanaged) {
 	CSharpScriptBinding &script_binding = ((Map<Object *, CSharpScriptBinding>::Element *)data)->value();
 
 	if (!script_binding.inited) {
-		SCOPED_MUTEX_LOCK(CSharpLanguage::get_singleton()->get_language_bind_mutex());
+		MutexLock lock(CSharpLanguage::get_singleton()->get_language_bind_mutex());
 
 		if (!script_binding.inited) { // Other thread may have set it up
 			// Already had a binding that needs to be setup
diff --git a/modules/mono/utils/mutex_utils.h b/modules/mono/utils/mutex_utils.h
deleted file mode 100644
index bafd875395..0000000000
--- a/modules/mono/utils/mutex_utils.h
+++ /dev/null
@@ -1,67 +0,0 @@
-/*************************************************************************/
-/*  mutex_utils.h                                                        */
-/*************************************************************************/
-/*                       This file is part of:                           */
-/*                           GODOT ENGINE                                */
-/*                      https://godotengine.org                          */
-/*************************************************************************/
-/* Copyright (c) 2007-2020 Juan Linietsky, Ariel Manzur.                 */
-/* Copyright (c) 2014-2020 Godot Engine contributors (cf. AUTHORS.md).   */
-/*                                                                       */
-/* 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 MUTEX_UTILS_H
-#define MUTEX_UTILS_H
-
-#include "core/error_macros.h"
-#include "core/os/mutex.h"
-
-#include "macros.h"
-
-class ScopedMutexLock {
-	Mutex *mutex;
-
-public:
-	ScopedMutexLock(Mutex *mutex) {
-		this->mutex = mutex;
-#ifndef NO_THREADS
-#ifdef DEBUG_ENABLED
-		CRASH_COND(!mutex);
-#endif
-		this->mutex->lock();
-#endif
-	}
-
-	~ScopedMutexLock() {
-#ifndef NO_THREADS
-#ifdef DEBUG_ENABLED
-		CRASH_COND(!mutex);
-#endif
-		mutex->unlock();
-#endif
-	}
-};
-
-#define SCOPED_MUTEX_LOCK(m_mutex) ScopedMutexLock GD_UNIQUE_NAME(__scoped_mutex_lock__)(m_mutex);
-
-// TODO: Add version that receives a lambda instead, once C++11 is allowed
-
-#endif // MUTEX_UTILS_H