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- `ShaderRD` contained an `std::mutex`, which has been replaced by `Mutex`.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, 6 insertions, 13 deletions

diff --git a/modules/gdscript/gdscript_function.cpp b/modules/gdscript/gdscript_function.cpp
index 27857ea91f..79c550c81c 100644
--- a/modules/gdscript/gdscript_function.cpp
+++ b/modules/gdscript/gdscript_function.cpp
@@ -1769,13 +1769,10 @@ GDScriptFunction::GDScriptFunction() :
 #ifdef DEBUG_ENABLED
 	_func_cname = NULL;
 
-	if (GDScriptLanguage::get_singleton()->lock) {
-		GDScriptLanguage::get_singleton()->lock->lock();
-	}
-	GDScriptLanguage::get_singleton()->function_list.add(&function_list);
+	{
+		MutexLock lock(GDScriptLanguage::get_singleton()->lock);
 
-	if (GDScriptLanguage::get_singleton()->lock) {
-		GDScriptLanguage::get_singleton()->lock->unlock();
+		GDScriptLanguage::get_singleton()->function_list.add(&function_list);
 	}
 
 	profile.call_count = 0;
@@ -1793,14 +1790,10 @@ GDScriptFunction::GDScriptFunction() :
 
 GDScriptFunction::~GDScriptFunction() {
 #ifdef DEBUG_ENABLED
-	if (GDScriptLanguage::get_singleton()->lock) {
-		GDScriptLanguage::get_singleton()->lock->lock();
-	}
-	GDScriptLanguage::get_singleton()->function_list.remove(&function_list);
 
-	if (GDScriptLanguage::get_singleton()->lock) {
-		GDScriptLanguage::get_singleton()->lock->unlock();
-	}
+	MutexLock lock(GDScriptLanguage::get_singleton()->lock);
+
+	GDScriptLanguage::get_singleton()->function_list.remove(&function_list);
 #endif
 }