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- `ShaderRD` contained an `std::mutex`, which has been replaced by `Mutex`.

17 files changed, 25 insertions, 373 deletions

diff --git a/drivers/alsa/audio_driver_alsa.cpp b/drivers/alsa/audio_driver_alsa.cpp
index fe6cd091b7..400ce31bf7 100644
--- a/drivers/alsa/audio_driver_alsa.cpp
+++ b/drivers/alsa/audio_driver_alsa.cpp
@@ -154,7 +154,6 @@ Error AudioDriverALSA::init() {
 
 	Error err = init_device();
 	if (err == OK) {
-		mutex = Mutex::create();
 		thread = Thread::create(AudioDriverALSA::thread_func, this);
 	}
 
@@ -299,16 +298,16 @@ void AudioDriverALSA::set_device(String device) {
 
 void AudioDriverALSA::lock() {
 
-	if (!thread || !mutex)
+	if (!thread)
 		return;
-	mutex->lock();
+	mutex.lock();
 }
 
 void AudioDriverALSA::unlock() {
 
-	if (!thread || !mutex)
+	if (!thread)
 		return;
-	mutex->unlock();
+	mutex.unlock();
 }
 
 void AudioDriverALSA::finish_device() {
@@ -327,11 +326,6 @@ void AudioDriverALSA::finish() {
 
 		memdelete(thread);
 		thread = NULL;
-
-		if (mutex) {
-			memdelete(mutex);
-			mutex = NULL;
-		}
 	}
 
 	finish_device();
@@ -339,7 +333,6 @@ void AudioDriverALSA::finish() {
 
 AudioDriverALSA::AudioDriverALSA() :
 		thread(NULL),
-		mutex(NULL),
 		pcm_handle(NULL),
 		device_name("Default"),
 		new_device("Default") {
diff --git a/drivers/alsa/audio_driver_alsa.h b/drivers/alsa/audio_driver_alsa.h
index fb793df6cd..a8caf0fbae 100644
--- a/drivers/alsa/audio_driver_alsa.h
+++ b/drivers/alsa/audio_driver_alsa.h
@@ -40,7 +40,7 @@
 class AudioDriverALSA : public AudioDriver {
 
 	Thread *thread;
-	Mutex *mutex;
+	Mutex mutex;
 
 	snd_pcm_t *pcm_handle;
 
diff --git a/drivers/alsamidi/midi_driver_alsamidi.cpp b/drivers/alsamidi/midi_driver_alsamidi.cpp
index 670d7e0a4a..0cecf1de3e 100644
--- a/drivers/alsamidi/midi_driver_alsamidi.cpp
+++ b/drivers/alsamidi/midi_driver_alsamidi.cpp
@@ -148,7 +148,6 @@ Error MIDIDriverALSAMidi::open() {
 	}
 	snd_device_name_free_hint(hints);
 
-	mutex = Mutex::create();
 	exit_thread = false;
 	thread = Thread::create(MIDIDriverALSAMidi::thread_func, this);
 
@@ -165,11 +164,6 @@ void MIDIDriverALSAMidi::close() {
 		thread = NULL;
 	}
 
-	if (mutex) {
-		memdelete(mutex);
-		mutex = NULL;
-	}
-
 	for (int i = 0; i < connected_inputs.size(); i++) {
 		snd_rawmidi_t *midi_in = connected_inputs[i];
 		snd_rawmidi_close(midi_in);
@@ -179,14 +173,12 @@ void MIDIDriverALSAMidi::close() {
 
 void MIDIDriverALSAMidi::lock() const {
 
-	if (mutex)
-		mutex->lock();
+	mutex.lock();
 }
 
 void MIDIDriverALSAMidi::unlock() const {
 
-	if (mutex)
-		mutex->unlock();
+	mutex.unlock();
 }
 
 PackedStringArray MIDIDriverALSAMidi::get_connected_inputs() {
@@ -210,7 +202,6 @@ PackedStringArray MIDIDriverALSAMidi::get_connected_inputs() {
 
 MIDIDriverALSAMidi::MIDIDriverALSAMidi() {
 
-	mutex = NULL;
 	thread = NULL;
 
 	exit_thread = false;
diff --git a/drivers/alsamidi/midi_driver_alsamidi.h b/drivers/alsamidi/midi_driver_alsamidi.h
index 9900d90553..6797c7c138 100644
--- a/drivers/alsamidi/midi_driver_alsamidi.h
+++ b/drivers/alsamidi/midi_driver_alsamidi.h
@@ -44,7 +44,7 @@
 class MIDIDriverALSAMidi : public MIDIDriver {
 
 	Thread *thread;
-	Mutex *mutex;
+	Mutex mutex;
 
 	Vector<snd_rawmidi_t *> connected_inputs;
 
diff --git a/drivers/coreaudio/audio_driver_coreaudio.cpp b/drivers/coreaudio/audio_driver_coreaudio.cpp
index d8229f7bf2..1e95bcf5d9 100644
--- a/drivers/coreaudio/audio_driver_coreaudio.cpp
+++ b/drivers/coreaudio/audio_driver_coreaudio.cpp
@@ -69,8 +69,6 @@ OSStatus AudioDriverCoreAudio::output_device_address_cb(AudioObjectID inObjectID
 #endif
 
 Error AudioDriverCoreAudio::init() {
-	mutex = Mutex::create();
-
 	AudioComponentDescription desc;
 	zeromem(&desc, sizeof(desc));
 	desc.componentType = kAudioUnitType_Output;
@@ -280,19 +278,15 @@ AudioDriver::SpeakerMode AudioDriverCoreAudio::get_speaker_mode() const {
 };
 
 void AudioDriverCoreAudio::lock() {
-	if (mutex)
-		mutex->lock();
+	mutex.lock();
 };
 
 void AudioDriverCoreAudio::unlock() {
-	if (mutex)
-		mutex->unlock();
+	mutex.unlock();
 };
 
 bool AudioDriverCoreAudio::try_lock() {
-	if (mutex)
-		return mutex->try_lock() == OK;
-	return true;
+	return mutex.try_lock() == OK;
 }
 
 void AudioDriverCoreAudio::finish() {
@@ -344,11 +338,6 @@ void AudioDriverCoreAudio::finish() {
 		audio_unit = NULL;
 		unlock();
 	}
-
-	if (mutex) {
-		memdelete(mutex);
-		mutex = NULL;
-	}
 }
 
 Error AudioDriverCoreAudio::capture_init() {
@@ -691,7 +680,6 @@ AudioDriverCoreAudio::AudioDriverCoreAudio() :
 		audio_unit(NULL),
 		input_unit(NULL),
 		active(false),
-		mutex(NULL),
 		device_name("Default"),
 		capture_device_name("Default"),
 		mix_rate(0),
diff --git a/drivers/coreaudio/audio_driver_coreaudio.h b/drivers/coreaudio/audio_driver_coreaudio.h
index 05aa759078..fb9473e230 100644
--- a/drivers/coreaudio/audio_driver_coreaudio.h
+++ b/drivers/coreaudio/audio_driver_coreaudio.h
@@ -46,7 +46,7 @@ class AudioDriverCoreAudio : public AudioDriver {
 	AudioComponentInstance input_unit;
 
 	bool active;
-	Mutex *mutex;
+	Mutex mutex;
 
 	String device_name;
 	String capture_device_name;
diff --git a/drivers/pulseaudio/audio_driver_pulseaudio.cpp b/drivers/pulseaudio/audio_driver_pulseaudio.cpp
index df9303fbec..ee9278fb8f 100644
--- a/drivers/pulseaudio/audio_driver_pulseaudio.cpp
+++ b/drivers/pulseaudio/audio_driver_pulseaudio.cpp
@@ -291,7 +291,6 @@ Error AudioDriverPulseAudio::init() {
 
 	Error err = init_device();
 	if (err == OK) {
-		mutex = Mutex::create();
 		thread = Thread::create(AudioDriverPulseAudio::thread_func, this);
 	}
 
@@ -597,16 +596,16 @@ void AudioDriverPulseAudio::set_device(String device) {
 
 void AudioDriverPulseAudio::lock() {
 
-	if (!thread || !mutex)
+	if (!thread)
 		return;
-	mutex->lock();
+	mutex.lock();
 }
 
 void AudioDriverPulseAudio::unlock() {
 
-	if (!thread || !mutex)
+	if (!thread)
 		return;
-	mutex->unlock();
+	mutex.unlock();
 }
 
 void AudioDriverPulseAudio::finish_device() {
@@ -640,10 +639,6 @@ void AudioDriverPulseAudio::finish() {
 	}
 
 	memdelete(thread);
-	if (mutex) {
-		memdelete(mutex);
-		mutex = NULL;
-	}
 
 	thread = NULL;
 }
@@ -800,7 +795,6 @@ String AudioDriverPulseAudio::capture_get_device() {
 
 AudioDriverPulseAudio::AudioDriverPulseAudio() :
 		thread(NULL),
-		mutex(NULL),
 		pa_ml(NULL),
 		pa_ctx(NULL),
 		pa_str(NULL),
diff --git a/drivers/pulseaudio/audio_driver_pulseaudio.h b/drivers/pulseaudio/audio_driver_pulseaudio.h
index 15948fa763..1ece332a8a 100644
--- a/drivers/pulseaudio/audio_driver_pulseaudio.h
+++ b/drivers/pulseaudio/audio_driver_pulseaudio.h
@@ -42,7 +42,7 @@
 class AudioDriverPulseAudio : public AudioDriver {
 
 	Thread *thread;
-	Mutex *mutex;
+	Mutex mutex;
 
 	pa_mainloop *pa_ml;
 	pa_context *pa_ctx;
diff --git a/drivers/unix/mutex_posix.cpp b/drivers/unix/mutex_posix.cpp
deleted file mode 100644
index a9fc12fb06..0000000000
--- a/drivers/unix/mutex_posix.cpp
+++ /dev/null
@@ -1,73 +0,0 @@
-/*************************************************************************/
-/*  mutex_posix.cpp                                                      */
-/*************************************************************************/
-/*                       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.                */
-/*************************************************************************/
-
-#include "mutex_posix.h"
-
-#include "core/os/memory.h"
-
-#if defined(UNIX_ENABLED) || defined(PTHREAD_ENABLED)
-
-void MutexPosix::lock() {
-
-	pthread_mutex_lock(&mutex);
-}
-void MutexPosix::unlock() {
-
-	pthread_mutex_unlock(&mutex);
-}
-Error MutexPosix::try_lock() {
-
-	return (pthread_mutex_trylock(&mutex) == 0) ? OK : ERR_BUSY;
-}
-
-Mutex *MutexPosix::create_func_posix(bool p_recursive) {
-
-	return memnew(MutexPosix(p_recursive));
-}
-
-void MutexPosix::make_default() {
-
-	create_func = create_func_posix;
-}
-
-MutexPosix::MutexPosix(bool p_recursive) {
-
-	pthread_mutexattr_init(&attr);
-	if (p_recursive)
-		pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE);
-	pthread_mutex_init(&mutex, &attr);
-}
-
-MutexPosix::~MutexPosix() {
-
-	pthread_mutex_destroy(&mutex);
-}
-
-#endif
diff --git a/drivers/unix/mutex_posix.h b/drivers/unix/mutex_posix.h
deleted file mode 100644
index bd67106836..0000000000
--- a/drivers/unix/mutex_posix.h
+++ /dev/null
@@ -1,61 +0,0 @@
-/*************************************************************************/
-/*  mutex_posix.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_POSIX_H
-#define MUTEX_POSIX_H
-
-#if defined(UNIX_ENABLED) || defined(PTHREAD_ENABLED)
-
-#include "core/os/mutex.h"
-
-#include <pthread.h>
-
-class MutexPosix : public Mutex {
-
-	pthread_mutexattr_t attr;
-	pthread_mutex_t mutex;
-
-	static Mutex *create_func_posix(bool p_recursive);
-
-public:
-	virtual void lock();
-	virtual void unlock();
-	virtual Error try_lock();
-
-	static void make_default();
-
-	MutexPosix(bool p_recursive);
-
-	~MutexPosix();
-};
-
-#endif
-
-#endif
diff --git a/drivers/unix/os_unix.cpp b/drivers/unix/os_unix.cpp
index 2d8d37b2f1..1d94b9618d 100644
--- a/drivers/unix/os_unix.cpp
+++ b/drivers/unix/os_unix.cpp
@@ -36,7 +36,6 @@
 #include "core/project_settings.h"
 #include "drivers/unix/dir_access_unix.h"
 #include "drivers/unix/file_access_unix.h"
-#include "drivers/unix/mutex_posix.h"
 #include "drivers/unix/net_socket_posix.h"
 #include "drivers/unix/rw_lock_posix.h"
 #include "drivers/unix/semaphore_posix.h"
@@ -123,14 +122,12 @@ void OS_Unix::initialize_core() {
 #ifdef NO_THREADS
 	ThreadDummy::make_default();
 	SemaphoreDummy::make_default();
-	MutexDummy::make_default();
 	RWLockDummy::make_default();
 #else
 	ThreadPosix::make_default();
 #if !defined(OSX_ENABLED) && !defined(IPHONE_ENABLED)
 	SemaphorePosix::make_default();
 #endif
-	MutexPosix::make_default();
 	RWLockPosix::make_default();
 #endif
 	FileAccess::make_default<FileAccessUnix>(FileAccess::ACCESS_RESOURCES);
diff --git a/drivers/wasapi/audio_driver_wasapi.cpp b/drivers/wasapi/audio_driver_wasapi.cpp
index 8aa6fb96c9..fa78771993 100644
--- a/drivers/wasapi/audio_driver_wasapi.cpp
+++ b/drivers/wasapi/audio_driver_wasapi.cpp
@@ -406,7 +406,6 @@ Error AudioDriverWASAPI::init() {
 	exit_thread = false;
 	thread_exited = false;
 
-	mutex = Mutex::create(true);
 	thread = Thread::create(thread_func, this);
 
 	return OK;
@@ -782,14 +781,12 @@ void AudioDriverWASAPI::start() {
 
 void AudioDriverWASAPI::lock() {
 
-	if (mutex)
-		mutex->lock();
+	mutex.lock();
 }
 
 void AudioDriverWASAPI::unlock() {
 
-	if (mutex)
-		mutex->unlock();
+	mutex.unlock();
 }
 
 void AudioDriverWASAPI::finish() {
@@ -804,11 +801,6 @@ void AudioDriverWASAPI::finish() {
 
 	finish_capture_device();
 	finish_render_device();
-
-	if (mutex) {
-		memdelete(mutex);
-		mutex = NULL;
-	}
 }
 
 Error AudioDriverWASAPI::capture_start() {
@@ -863,7 +855,6 @@ String AudioDriverWASAPI::capture_get_device() {
 
 AudioDriverWASAPI::AudioDriverWASAPI() {
 
-	mutex = NULL;
 	thread = NULL;
 
 	samples_in.clear();
diff --git a/drivers/wasapi/audio_driver_wasapi.h b/drivers/wasapi/audio_driver_wasapi.h
index ebceedd431..3ea61c6010 100644
--- a/drivers/wasapi/audio_driver_wasapi.h
+++ b/drivers/wasapi/audio_driver_wasapi.h
@@ -75,7 +75,7 @@ class AudioDriverWASAPI : public AudioDriver {
 	AudioDeviceWASAPI audio_input;
 	AudioDeviceWASAPI audio_output;
 
-	Mutex *mutex;
+	Mutex mutex;
 	Thread *thread;
 
 	Vector<int32_t> samples_in;
diff --git a/drivers/windows/mutex_windows.cpp b/drivers/windows/mutex_windows.cpp
deleted file mode 100644
index 1f14adb48f..0000000000
--- a/drivers/windows/mutex_windows.cpp
+++ /dev/null
@@ -1,101 +0,0 @@
-/*************************************************************************/
-/*  mutex_windows.cpp                                                    */
-/*************************************************************************/
-/*                       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.                */
-/*************************************************************************/
-
-#include "mutex_windows.h"
-
-#include "core/os/memory.h"
-
-#ifdef WINDOWS_ENABLED
-
-void MutexWindows::lock() {
-
-#ifdef WINDOWS_USE_MUTEX
-	WaitForSingleObject(mutex, INFINITE);
-#else
-	EnterCriticalSection(&mutex);
-#endif
-}
-
-void MutexWindows::unlock() {
-
-#ifdef WINDOWS_USE_MUTEX
-	ReleaseMutex(mutex);
-#else
-	LeaveCriticalSection(&mutex);
-#endif
-}
-
-Error MutexWindows::try_lock() {
-
-#ifdef WINDOWS_USE_MUTEX
-	return (WaitForSingleObject(mutex, 0) == WAIT_TIMEOUT) ? ERR_BUSY : OK;
-#else
-
-	if (TryEnterCriticalSection(&mutex))
-		return OK;
-	else
-		return ERR_BUSY;
-#endif
-}
-
-Mutex *MutexWindows::create_func_windows(bool p_recursive) {
-
-	return memnew(MutexWindows);
-}
-
-void MutexWindows::make_default() {
-
-	create_func = create_func_windows;
-}
-
-MutexWindows::MutexWindows() {
-
-#ifdef WINDOWS_USE_MUTEX
-	mutex = CreateMutex(NULL, FALSE, NULL);
-#else
-#ifdef UWP_ENABLED
-	InitializeCriticalSectionEx(&mutex, 0, 0);
-#else
-	InitializeCriticalSection(&mutex);
-#endif
-#endif
-}
-
-MutexWindows::~MutexWindows() {
-
-#ifdef WINDOWS_USE_MUTEX
-	CloseHandle(mutex);
-#else
-
-	DeleteCriticalSection(&mutex);
-#endif
-}
-
-#endif
diff --git a/drivers/windows/mutex_windows.h b/drivers/windows/mutex_windows.h
deleted file mode 100644
index 28b97540b7..0000000000
--- a/drivers/windows/mutex_windows.h
+++ /dev/null
@@ -1,63 +0,0 @@
-/*************************************************************************/
-/*  mutex_windows.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_WINDOWS_H
-#define MUTEX_WINDOWS_H
-
-#ifdef WINDOWS_ENABLED
-
-#include "core/os/mutex.h"
-
-#include <windows.h>
-
-class MutexWindows : public Mutex {
-
-#ifdef WINDOWS_USE_MUTEX
-	HANDLE mutex;
-#else
-	CRITICAL_SECTION mutex;
-#endif
-
-	static Mutex *create_func_windows(bool p_recursive);
-
-public:
-	virtual void lock();
-	virtual void unlock();
-	virtual Error try_lock();
-
-	static void make_default();
-
-	MutexWindows();
-	~MutexWindows();
-};
-
-#endif
-
-#endif
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];