Modernize RWLock

- Based on C++14's `shared_time_mutex`
- No more need to allocate-deallocate or check for null
- No pointer anymore, just a member variable
- Platform-specific implementations no longer needed
- Simpler for `NO_THREADS`

10 files changed, 102 insertions, 192 deletions

diff --git a/core/io/resource.cpp b/core/io/resource.cpp
index 2c97e617f2..db79998a90 100644
--- a/core/io/resource.cpp
+++ b/core/io/resource.cpp
@@ -52,29 +52,29 @@ void Resource::set_path(const String &p_path, bool p_take_over) {
 	}
 
 	if (path_cache != "") {
-		ResourceCache::lock->write_lock();
+		ResourceCache::lock.write_lock();
 		ResourceCache::resources.erase(path_cache);
-		ResourceCache::lock->write_unlock();
+		ResourceCache::lock.write_unlock();
 	}
 
 	path_cache = "";
 
-	ResourceCache::lock->read_lock();
+	ResourceCache::lock.read_lock();
 	bool has_path = ResourceCache::resources.has(p_path);
-	ResourceCache::lock->read_unlock();
+	ResourceCache::lock.read_unlock();
 
 	if (has_path) {
 		if (p_take_over) {
-			ResourceCache::lock->write_lock();
+			ResourceCache::lock.write_lock();
 			Resource **res = ResourceCache::resources.getptr(p_path);
 			if (res) {
 				(*res)->set_name("");
 			}
-			ResourceCache::lock->write_unlock();
+			ResourceCache::lock.write_unlock();
 		} else {
-			ResourceCache::lock->read_lock();
+			ResourceCache::lock.read_lock();
 			bool exists = ResourceCache::resources.has(p_path);
-			ResourceCache::lock->read_unlock();
+			ResourceCache::lock.read_unlock();
 
 			ERR_FAIL_COND_MSG(exists, "Another resource is loaded from path '" + p_path + "' (possible cyclic resource inclusion).");
 		}
@@ -82,9 +82,9 @@ void Resource::set_path(const String &p_path, bool p_take_over) {
 	path_cache = p_path;
 
 	if (path_cache != "") {
-		ResourceCache::lock->write_lock();
+		ResourceCache::lock.write_lock();
 		ResourceCache::resources[path_cache] = this;
-		ResourceCache::lock->write_unlock();
+		ResourceCache::lock.write_unlock();
 	}
 
 	_change_notify("resource_path");
@@ -315,9 +315,7 @@ void Resource::set_as_translation_remapped(bool p_remapped) {
 		return;
 	}
 
-	if (ResourceCache::lock) {
-		ResourceCache::lock->write_lock();
-	}
+	ResourceCache::lock.write_lock();
 
 	if (p_remapped) {
 		ResourceLoader::remapped_list.add(&remapped_list);
@@ -325,9 +323,7 @@ void Resource::set_as_translation_remapped(bool p_remapped) {
 		ResourceLoader::remapped_list.remove(&remapped_list);
 	}
 
-	if (ResourceCache::lock) {
-		ResourceCache::lock->write_unlock();
-	}
+	ResourceCache::lock.write_unlock();
 }
 
 bool Resource::is_translation_remapped() const {
@@ -338,38 +334,24 @@ bool Resource::is_translation_remapped() const {
 //helps keep IDs same number when loading/saving scenes. -1 clears ID and it Returns -1 when no id stored
 void Resource::set_id_for_path(const String &p_path, int p_id) {
 	if (p_id == -1) {
-		if (ResourceCache::path_cache_lock) {
-			ResourceCache::path_cache_lock->write_lock();
-		}
+		ResourceCache::path_cache_lock.write_lock();
 		ResourceCache::resource_path_cache[p_path].erase(get_path());
-		if (ResourceCache::path_cache_lock) {
-			ResourceCache::path_cache_lock->write_unlock();
-		}
+		ResourceCache::path_cache_lock.write_unlock();
 	} else {
-		if (ResourceCache::path_cache_lock) {
-			ResourceCache::path_cache_lock->write_lock();
-		}
+		ResourceCache::path_cache_lock.write_lock();
 		ResourceCache::resource_path_cache[p_path][get_path()] = p_id;
-		if (ResourceCache::path_cache_lock) {
-			ResourceCache::path_cache_lock->write_unlock();
-		}
+		ResourceCache::path_cache_lock.write_unlock();
 	}
 }
 
 int Resource::get_id_for_path(const String &p_path) const {
-	if (ResourceCache::path_cache_lock) {
-		ResourceCache::path_cache_lock->read_lock();
-	}
+	ResourceCache::path_cache_lock.read_lock();
 	if (ResourceCache::resource_path_cache[p_path].has(get_path())) {
 		int result = ResourceCache::resource_path_cache[p_path][get_path()];
-		if (ResourceCache::path_cache_lock) {
-			ResourceCache::path_cache_lock->read_unlock();
-		}
+		ResourceCache::path_cache_lock.read_unlock();
 		return result;
 	} else {
-		if (ResourceCache::path_cache_lock) {
-			ResourceCache::path_cache_lock->read_unlock();
-		}
+		ResourceCache::path_cache_lock.read_unlock();
 		return -1;
 	}
 }
@@ -403,9 +385,9 @@ Resource::Resource() :
 
 Resource::~Resource() {
 	if (path_cache != "") {
-		ResourceCache::lock->write_lock();
+		ResourceCache::lock.write_lock();
 		ResourceCache::resources.erase(path_cache);
-		ResourceCache::lock->write_unlock();
+		ResourceCache::lock.write_unlock();
 	}
 	if (owners.size()) {
 		WARN_PRINT("Resource is still owned.");
@@ -417,18 +399,11 @@ HashMap<String, Resource *> ResourceCache::resources;
 HashMap<String, HashMap<String, int>> ResourceCache::resource_path_cache;
 #endif
 
-RWLock *ResourceCache::lock = nullptr;
+RWLock ResourceCache::lock;
 #ifdef TOOLS_ENABLED
-RWLock *ResourceCache::path_cache_lock = nullptr;
+RWLock ResourceCache::path_cache_lock;
 #endif
 
-void ResourceCache::setup() {
-	lock = RWLock::create();
-#ifdef TOOLS_ENABLED
-	path_cache_lock = RWLock::create();
-#endif
-}
-
 void ResourceCache::clear() {
 	if (resources.size()) {
 		ERR_PRINT("Resources still in use at exit (run with --verbose for details).");
@@ -442,29 +417,25 @@ void ResourceCache::clear() {
 	}
 
 	resources.clear();
-	memdelete(lock);
-#ifdef TOOLS_ENABLED
-	memdelete(path_cache_lock);
-#endif
 }
 
 void ResourceCache::reload_externals() {
 }
 
 bool ResourceCache::has(const String &p_path) {
-	lock->read_lock();
+	lock.read_lock();
 	bool b = resources.has(p_path);
-	lock->read_unlock();
+	lock.read_unlock();
 
 	return b;
 }
 
 Resource *ResourceCache::get(const String &p_path) {
-	lock->read_lock();
+	lock.read_lock();
 
 	Resource **res = resources.getptr(p_path);
 
-	lock->read_unlock();
+	lock.read_unlock();
 
 	if (!res) {
 		return nullptr;
@@ -474,26 +445,26 @@ Resource *ResourceCache::get(const String &p_path) {
 }
 
 void ResourceCache::get_cached_resources(List<Ref<Resource>> *p_resources) {
-	lock->read_lock();
+	lock.read_lock();
 	const String *K = nullptr;
 	while ((K = resources.next(K))) {
 		Resource *r = resources[*K];
 		p_resources->push_back(Ref<Resource>(r));
 	}
-	lock->read_unlock();
+	lock.read_unlock();
 }
 
 int ResourceCache::get_cached_resource_count() {
-	lock->read_lock();
+	lock.read_lock();
 	int rc = resources.size();
-	lock->read_unlock();
+	lock.read_unlock();
 
 	return rc;
 }
 
 void ResourceCache::dump(const char *p_file, bool p_short) {
 #ifdef DEBUG_ENABLED
-	lock->read_lock();
+	lock.read_lock();
 
 	Map<String, int> type_count;
 
@@ -530,6 +501,6 @@ void ResourceCache::dump(const char *p_file, bool p_short) {
 		memdelete(f);
 	}
 
-	lock->read_unlock();
+	lock.read_unlock();
 #endif
 }
diff --git a/core/io/resource.h b/core/io/resource.h
index eda18a8538..d0cd6ea3ac 100644
--- a/core/io/resource.h
+++ b/core/io/resource.h
@@ -149,16 +149,15 @@ typedef Ref<Resource> RES;
 class ResourceCache {
 	friend class Resource;
 	friend class ResourceLoader; //need the lock
-	static RWLock *lock;
+	static RWLock lock;
 	static HashMap<String, Resource *> resources;
 #ifdef TOOLS_ENABLED
 	static HashMap<String, HashMap<String, int>> resource_path_cache; // each tscn has a set of resource paths and IDs
-	static RWLock *path_cache_lock;
+	static RWLock path_cache_lock;
 #endif // TOOLS_ENABLED
 	friend void unregister_core_types();
 	static void clear();
 	friend void register_core_types();
-	static void setup();
 
 public:
 	static void reload_externals();
diff --git a/core/io/resource_loader.cpp b/core/io/resource_loader.cpp
index 821e468aee..1a2b1ed033 100644
--- a/core/io/resource_loader.cpp
+++ b/core/io/resource_loader.cpp
@@ -323,9 +323,7 @@ Error ResourceLoader::load_threaded_request(const String &p_path, const String &
 				ERR_FAIL_V_MSG(ERR_INVALID_PARAMETER, "Attempted to load a resource already being loaded from this thread, cyclic reference?");
 			}
 			//lock first if possible
-			if (ResourceCache::lock) {
-				ResourceCache::lock->read_lock();
-			}
+			ResourceCache::lock.read_lock();
 
 			//get ptr
 			Resource **rptr = ResourceCache::resources.getptr(local_path);
@@ -340,9 +338,7 @@ Error ResourceLoader::load_threaded_request(const String &p_path, const String &
 					load_task.progress = 1.0;
 				}
 			}
-			if (ResourceCache::lock) {
-				ResourceCache::lock->read_unlock();
-			}
+			ResourceCache::lock.read_unlock();
 		}
 
 		if (p_source_resource != String()) {
@@ -535,9 +531,7 @@ RES ResourceLoader::load(const String &p_path, const String &p_type_hint, bool p
 		}
 
 		//Is it cached?
-		if (ResourceCache::lock) {
-			ResourceCache::lock->read_lock();
-		}
+		ResourceCache::lock.read_lock();
 
 		Resource **rptr = ResourceCache::resources.getptr(local_path);
 
@@ -546,9 +540,7 @@ RES ResourceLoader::load(const String &p_path, const String &p_type_hint, bool p
 
 			//it is possible this resource was just freed in a thread. If so, this referencing will not work and resource is considered not cached
 			if (res.is_valid()) {
-				if (ResourceCache::lock) {
-					ResourceCache::lock->read_unlock();
-				}
+				ResourceCache::lock.read_unlock();
 				thread_load_mutex->unlock();
 
 				if (r_error) {
@@ -559,9 +551,7 @@ RES ResourceLoader::load(const String &p_path, const String &p_type_hint, bool p
 			}
 		}
 
-		if (ResourceCache::lock) {
-			ResourceCache::lock->read_unlock();
-		}
+		ResourceCache::lock.read_unlock();
 
 		//load using task (but this thread)
 		ThreadLoadTask load_task;
@@ -955,9 +945,7 @@ String ResourceLoader::path_remap(const String &p_path) {
 }
 
 void ResourceLoader::reload_translation_remaps() {
-	if (ResourceCache::lock) {
-		ResourceCache::lock->read_lock();
-	}
+	ResourceCache::lock.read_lock();
 
 	List<Resource *> to_reload;
 	SelfList<Resource> *E = remapped_list.first();
@@ -967,9 +955,7 @@ void ResourceLoader::reload_translation_remaps() {
 		E = E->next();
 	}
 
-	if (ResourceCache::lock) {
-		ResourceCache::lock->read_unlock();
-	}
+	ResourceCache::lock.read_unlock();
 
 	//now just make sure to not delete any of these resources while changing locale..
 	while (to_reload.front()) {
diff --git a/core/object/class_db.cpp b/core/object/class_db.cpp
index 6bc6d653d1..375ad8fae1 100644
--- a/core/object/class_db.cpp
+++ b/core/object/class_db.cpp
@@ -983,9 +983,9 @@ void ClassDB::add_property_subgroup(StringName p_class, const String &p_name, co
 
 // NOTE: For implementation simplicity reasons, this method doesn't allow setters to have optional arguments at the end.
 void ClassDB::add_property(StringName p_class, const PropertyInfo &p_pinfo, const StringName &p_setter, const StringName &p_getter, int p_index) {
-	lock->read_lock();
+	lock.read_lock();
 	ClassInfo *type = classes.getptr(p_class);
-	lock->read_unlock();
+	lock.read_unlock();
 
 	ERR_FAIL_COND(!type);
 
@@ -1541,11 +1541,7 @@ Variant ClassDB::class_get_default_property_value(const StringName &p_class, con
 	return var;
 }
 
-RWLock *ClassDB::lock = nullptr;
-
-void ClassDB::init() {
-	lock = RWLock::create();
-}
+RWLock ClassDB::lock;
 
 void ClassDB::cleanup_defaults() {
 	default_values.clear();
@@ -1568,8 +1564,6 @@ void ClassDB::cleanup() {
 	classes.clear();
 	resource_base_extensions.clear();
 	compat_classes.clear();
-
-	memdelete(lock);
 }
 
 //
diff --git a/core/object/class_db.h b/core/object/class_db.h
index 0591676b92..6fd5748dbb 100644
--- a/core/object/class_db.h
+++ b/core/object/class_db.h
@@ -146,7 +146,7 @@ public:
 		return memnew(T);
 	}
 
-	static RWLock *lock;
+	static RWLock lock;
 	static HashMap<StringName, ClassInfo> classes;
 	static HashMap<StringName, StringName> resource_base_extensions;
 	static HashMap<StringName, StringName> compat_classes;
@@ -387,7 +387,6 @@ public:
 	static void get_extensions_for_type(const StringName &p_class, List<String> *p_extensions);
 
 	static void add_compatibility_class(const StringName &p_class, const StringName &p_fallback);
-	static void init();
 
 	static void set_current_api(APIType p_api);
 	static APIType get_current_api();
diff --git a/core/os/rw_lock.cpp b/core/os/rw_lock.cpp
deleted file mode 100644
index 26db0aab30..0000000000
--- a/core/os/rw_lock.cpp
+++ /dev/null
@@ -1,43 +0,0 @@
-/*************************************************************************/
-/*  rw_lock.cpp                                                          */
-/*************************************************************************/
-/*                       This file is part of:                           */
-/*                           GODOT ENGINE                                */
-/*                      https://godotengine.org                          */
-/*************************************************************************/
-/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur.                 */
-/* Copyright (c) 2014-2021 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.                */
-/*************************************************************************/
-
-#include "rw_lock.h"
-
-#include "core/error/error_macros.h"
-
-#include <stddef.h>
-
-RWLock *(*RWLock::create_func)() = nullptr;
-
-RWLock *RWLock::create() {
-	ERR_FAIL_COND_V(!create_func, nullptr);
-
-	return create_func();
-}
diff --git a/core/os/rw_lock.h b/core/os/rw_lock.h
index ff6ad3cc4a..560ec57a5f 100644
--- a/core/os/rw_lock.h
+++ b/core/os/rw_lock.h
@@ -33,55 +33,83 @@
 
 #include "core/error/error_list.h"
 
+#if !defined(NO_THREADS)
+
+#include <shared_mutex>
+
 class RWLock {
-protected:
-	static RWLock *(*create_func)();
+	mutable std::shared_timed_mutex mutex;
 
 public:
-	virtual void read_lock() = 0; ///< Lock the rwlock, block if locked by someone else
-	virtual void read_unlock() = 0; ///< Unlock the rwlock, let other threads continue
-	virtual Error read_try_lock() = 0; ///< Attempt to lock the rwlock, OK on success, ERROR means it can't lock.
+	// Lock the rwlock, block if locked by someone else
+	void read_lock() const {
+		mutex.lock_shared();
+	}
 
-	virtual void write_lock() = 0; ///< Lock the rwlock, block if locked by someone else
-	virtual void write_unlock() = 0; ///< Unlock the rwlock, let other thwrites continue
-	virtual Error write_try_lock() = 0; ///< Attempt to lock the rwlock, OK on success, ERROR means it can't lock.
+	// Unlock the rwlock, let other threads continue
+	void read_unlock() const {
+		mutex.unlock_shared();
+	}
 
-	static RWLock *create(); ///< Create a rwlock
+	// Attempt to lock the rwlock, OK on success, ERR_BUSY means it can't lock.
+	Error read_try_lock() const {
+		return mutex.try_lock_shared() ? OK : ERR_BUSY;
+	}
+
+	// Lock the rwlock, block if locked by someone else
+	void write_lock() {
+		mutex.lock();
+	}
+
+	// Unlock the rwlock, let other thwrites continue
+	void write_unlock() {
+		mutex.unlock();
+	}
 
-	virtual ~RWLock() {}
+	// Attempt to lock the rwlock, OK on success, ERR_BUSY means it can't lock.
+	Error write_try_lock() {
+		return mutex.try_lock() ? OK : ERR_BUSY;
+	}
+};
+
+#else
+
+class RWLock {
+public:
+	void read_lock() const {}
+	void read_unlock() const {}
+	Error read_try_lock() const { return OK; }
+
+	void write_lock() {}
+	void write_unlock() {}
+	Error write_try_lock() { return OK; }
 };
 
+#endif
+
 class RWLockRead {
-	RWLock *lock;
+	const RWLock &lock;
 
 public:
-	RWLockRead(const RWLock *p_lock) {
-		lock = const_cast<RWLock *>(p_lock);
-		if (lock) {
-			lock->read_lock();
-		}
+	RWLockRead(const RWLock &p_lock) :
+			lock(p_lock) {
+		lock.read_lock();
 	}
 	~RWLockRead() {
-		if (lock) {
-			lock->read_unlock();
-		}
+		lock.read_unlock();
 	}
 };
 
 class RWLockWrite {
-	RWLock *lock;
+	RWLock &lock;
 
 public:
-	RWLockWrite(RWLock *p_lock) {
-		lock = p_lock;
-		if (lock) {
-			lock->write_lock();
-		}
+	RWLockWrite(RWLock &p_lock) :
+			lock(p_lock) {
+		lock.write_lock();
 	}
 	~RWLockWrite() {
-		if (lock) {
-			lock->write_unlock();
-		}
+		lock.write_unlock();
 	}
 };
 
diff --git a/core/os/thread_dummy.cpp b/core/os/thread_dummy.cpp
index 006757b8e4..a72e1298d1 100644
--- a/core/os/thread_dummy.cpp
+++ b/core/os/thread_dummy.cpp
@@ -39,11 +39,3 @@ Thread *ThreadDummy::create(ThreadCreateCallback p_callback, void *p_user, const
 void ThreadDummy::make_default() {
 	Thread::create_func = &ThreadDummy::create;
 }
-
-RWLock *RWLockDummy::create() {
-	return memnew(RWLockDummy);
-}
-
-void RWLockDummy::make_default() {
-	RWLock::create_func = &RWLockDummy::create;
-}
diff --git a/core/os/thread_dummy.h b/core/os/thread_dummy.h
index 35e19732bf..0bd59ea309 100644
--- a/core/os/thread_dummy.h
+++ b/core/os/thread_dummy.h
@@ -44,19 +44,4 @@ public:
 	static void make_default();
 };
 
-class RWLockDummy : public RWLock {
-	static RWLock *create();
-
-public:
-	virtual void read_lock() {}
-	virtual void read_unlock() {}
-	virtual Error read_try_lock() { return OK; }
-
-	virtual void write_lock() {}
-	virtual void write_unlock() {}
-	virtual Error write_try_lock() { return OK; }
-
-	static void make_default();
-};
-
 #endif // THREAD_DUMMY_H
diff --git a/core/register_core_types.cpp b/core/register_core_types.cpp
index 9eef7700f9..b58abc81d1 100644
--- a/core/register_core_types.cpp
+++ b/core/register_core_types.cpp
@@ -103,7 +103,6 @@ void register_core_types() {
 	static_assert(sizeof(Callable) <= 16);
 
 	ObjectDB::setup();
-	ResourceCache::setup();
 
 	StringName::setup();
 	ResourceLoader::initialize();