Fix intermittent corruption uploading textures in Dota 2.

The problem was that MVKBuffer::getMTLBuffer() was not thread-safe.  If
multiple threads called it at the same time, more than one underlying
_mtlBuffer would be created.  This could make the vkCmdCopyBufferToImage
copy from an unfilled buffer leaving the texture corrupted.  I also
added similar thread safety to MVKImage::getMTLTexture() and
MVKImageView::getMTLTexture() since they both looked like they would
have the same potential problem.

MoltenVK/MoltenVK/GPUObjects/MVKBuffer.h

@@ -79,6 +79,7 @@ protected:
 						   VkBufferMemoryBarrier* pBufferMemoryBarrier);
 
     id<MTLBuffer> _mtlBuffer;
+    std::mutex _lock;
 };
 
 

MoltenVK/MoltenVK/GPUObjects/MVKBuffer.mm

@@ -154,6 +154,13 @@ id<MTLBuffer> MVKBuffer::getMTLBuffer() {
 
     if (_mtlBuffer) { return _mtlBuffer; }
 
+    lock_guard<mutex> lock(_lock);
+
+    // Check again in case another thread has created the buffer.
+    if (_mtlBuffer) {
+        return _mtlBuffer;
+    }
+
     id<MTLBuffer> devMemMTLBuff = _deviceMemory->getMTLBuffer();
     if (devMemMTLBuff) { return devMemMTLBuff; }
 

MoltenVK/MoltenVK/GPUObjects/MVKImage.h

@@ -222,6 +222,7 @@ protected:
 	MTLPixelFormat _mtlPixelFormat;
 	MTLTextureType _mtlTextureType;
     id<MTLTexture> _mtlTexture;
+    std::mutex _lock;
     IOSurfaceRef _ioSurface;
     bool _isDepthStencilAttachment;
 	bool _canSupportMTLTextureView;
@@ -279,6 +280,7 @@ protected:
     MVKImage* _image;
     VkImageSubresourceRange _subresourceRange;
 	id<MTLTexture> _mtlTexture;
+	std::mutex _lock;
 	MTLPixelFormat _mtlPixelFormat;
 	MTLTextureType _mtlTextureType;
 	bool _useMTLTextureView;

MoltenVK/MoltenVK/GPUObjects/MVKImage.mm

@@ -215,7 +215,13 @@ void* MVKImage::map(VkDeviceSize offset, VkDeviceSize size) {
 #pragma mark Metal
 
 id<MTLTexture> MVKImage::getMTLTexture() {
-	if ( !_mtlTexture && _mtlPixelFormat ) { _mtlTexture = newMTLTexture(); }   // retained
+	if ( !_mtlTexture && _mtlPixelFormat ) {
+		lock_guard<mutex> lock(_lock);
+		// Check again in case another thread has created the texture.
+		if ( !_mtlTexture ) {
+			_mtlTexture = newMTLTexture();
+		}
+	}   // retained
 	return _mtlTexture;
 }
 
@@ -537,7 +543,13 @@ void MVKImageView::populateMTLRenderPassAttachmentDescriptorResolve(MTLRenderPas
 id<MTLTexture> MVKImageView::getMTLTexture() {
 	// If we can use a Metal texture view, lazily create it, otherwise use the image texture directly.
 	if (_useMTLTextureView) {
-		if ( !_mtlTexture && _mtlPixelFormat ) { _mtlTexture = newMTLTexture(); }		// retained
+		if ( !_mtlTexture && _mtlPixelFormat ) {
+			lock_guard<mutex> lock(_lock);
+			// Check again in case another thread created the texture view
+			if ( !_mtlTexture ) {
+				_mtlTexture = newMTLTexture(); // retained
+			}
+		}
 		return _mtlTexture;
 	} else {
 		return _image->getMTLTexture();