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- `ShaderRD` contained an `std::mutex`, which has been replaced by `Mutex`.

2 files changed, 5 insertions, 9 deletions

diff --git a/drivers/xaudio2/audio_driver_xaudio2.cpp b/drivers/xaudio2/audio_driver_xaudio2.cpp
index 85e505009b..9c7cb4f0f3 100644
--- a/drivers/xaudio2/audio_driver_xaudio2.cpp
+++ b/drivers/xaudio2/audio_driver_xaudio2.cpp
@@ -79,7 +79,6 @@ Error AudioDriverXAudio2::init() {
 	hr = xaudio->CreateSourceVoice(&source_voice, &wave_format, 0, XAUDIO2_MAX_FREQ_RATIO, &voice_callback);
 	ERR_FAIL_COND_V_MSG(hr != S_OK, ERR_UNAVAILABLE, "Error creating XAudio2 source voice. Error code: " + itos(hr) + ".");
 
-	mutex = Mutex::create();
 	thread = Thread::create(AudioDriverXAudio2::thread_func, this);
 
 	return OK;
@@ -158,15 +157,15 @@ float AudioDriverXAudio2::get_latency() {
 
 void AudioDriverXAudio2::lock() {
 
-	if (!thread || !mutex)
+	if (!thread)
 		return;
-	mutex->lock();
+	mutex.lock();
 }
 void AudioDriverXAudio2::unlock() {
 
-	if (!thread || !mutex)
+	if (!thread)
 		return;
-	mutex->unlock();
+	mutex.unlock();
 }
 
 void AudioDriverXAudio2::finish() {
@@ -194,14 +193,11 @@ void AudioDriverXAudio2::finish() {
 	mastering_voice->DestroyVoice();
 
 	memdelete(thread);
-	if (mutex)
-		memdelete(mutex);
 	thread = NULL;
 }
 
 AudioDriverXAudio2::AudioDriverXAudio2() :
 		thread(NULL),
-		mutex(NULL),
 		current_buffer(0) {
 	wave_format = { 0 };
 	for (int i = 0; i < AUDIO_BUFFERS; i++) {
diff --git a/drivers/xaudio2/audio_driver_xaudio2.h b/drivers/xaudio2/audio_driver_xaudio2.h
index 98950851d0..108891a288 100644
--- a/drivers/xaudio2/audio_driver_xaudio2.h
+++ b/drivers/xaudio2/audio_driver_xaudio2.h
@@ -65,7 +65,7 @@ class AudioDriverXAudio2 : public AudioDriver {
 	};
 
 	Thread *thread;
-	Mutex *mutex;
+	Mutex mutex;
 
 	int32_t *samples_in;
 	int16_t *samples_out[AUDIO_BUFFERS];