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- `ShaderRD` contained an `std::mutex`, which has been replaced by `Mutex`.

1 files changed, 8 insertions, 18 deletions

diff --git a/modules/visual_script/visual_script.cpp b/modules/visual_script/visual_script.cpp
index 70f650cfd3..5036840413 100644
--- a/modules/visual_script/visual_script.cpp
+++ b/modules/visual_script/visual_script.cpp
@@ -928,13 +928,11 @@ ScriptInstance *VisualScript::instance_create(Object *p_this) {
 	VisualScriptInstance *instance = memnew(VisualScriptInstance);
 	instance->create(Ref<VisualScript>(this), p_this);
 
-	if (VisualScriptLanguage::singleton->lock)
-		VisualScriptLanguage::singleton->lock->lock();
-
-	instances[p_this] = instance;
+	{
+		MutexLock lock(VisualScriptLanguage::singleton->lock);
 
-	if (VisualScriptLanguage::singleton->lock)
-		VisualScriptLanguage::singleton->lock->unlock();
+		instances[p_this] = instance;
+	}
 
 	return instance;
 }
@@ -2391,13 +2389,11 @@ VisualScriptInstance::VisualScriptInstance() {
 
 VisualScriptInstance::~VisualScriptInstance() {
 
-	if (VisualScriptLanguage::singleton->lock)
-		VisualScriptLanguage::singleton->lock->lock();
-
-	script->instances.erase(owner);
+	{
+		MutexLock lock(VisualScriptLanguage::singleton->lock);
 
-	if (VisualScriptLanguage::singleton->lock)
-		VisualScriptLanguage::singleton->lock->unlock();
+		script->instances.erase(owner);
+	}
 
 	for (Map<int, VisualScriptNodeInstance *>::Element *E = instances.front(); E; E = E->next()) {
 		memdelete(E->get());
@@ -2836,9 +2832,6 @@ VisualScriptLanguage::VisualScriptLanguage() {
 	_step = "_step";
 	_subcall = "_subcall";
 	singleton = this;
-#ifndef NO_THREADS
-	lock = Mutex::create();
-#endif
 
 	_debug_parse_err_node = -1;
 	_debug_parse_err_file = "";
@@ -2859,9 +2852,6 @@ VisualScriptLanguage::VisualScriptLanguage() {
 
 VisualScriptLanguage::~VisualScriptLanguage() {
 
-	if (lock)
-		memdelete(lock);
-
 	if (_call_stack) {
 		memdelete_arr(_call_stack);
 	}