How to deallocate a MTLBuffer and MTLTexture

Question

I know how to create a MTLBuffer and or MTLTexture but how do I free the GPU memory for these resources when they are no longer needed?

Answer 1

MTLBuffer and MTLTexture are Objective-C objects and thus reference counted. If you are using automatic reference counting in an Objective-C project or using Metal via Swift, simply ensuring you no longer hold references to the buffer or texture will release any associated hardware resources.

let texture: MTLTexture? = device.newTexture(with: descriptor)
texture = nil // <- resources will be released

One can confirm this by stepping through the associated assembly when assigning nil to texture, which first leads us to [MTLDebugTexture dealloc]

MetalTools`-[MTLDebugTexture dealloc]:
    ...
->  0x100af569e <+34>: call   0x100af87ee               ; symbol stub for: objc_msgSendSuper2
    0x100af56a3 <+39>: add    rsp, 0x10
    0x100af56a7 <+43>: pop    rbp
    0x100af56a8 <+44>: ret    

...and through [MTLToolsObject dealloc]

MetalTools`-[MTLToolsObject dealloc]:
    0x100ac6c7a <+0>:   push   rbp
    0x100ac6c7b <+1>:   mov    rbp, rsp
    0x100ac6c7e <+4>:   push   r14
    ...

...and through the GeForceMTLDriver

GeForceMTLDriver`___lldb_unnamed_symbol1095$$GeForceMTLDriver:
->  0x7fffd2e57b14 <+0>:  push   rbp
    0x7fffd2e57b15 <+1>:  mov    rbp, rsp

All the way, releasing any resources through the various dealloc methods.

Answer 2

If you are using automatic reference counting, as the accepted answer said, just set nil.

But if you are using manual reference counting, Metal has two kinds of dynamically allocated resources(MTLBuffer && MTLTexture) and you can release them in below way.

id<MTLDevice> m_Device = MTLCreateSystemDefaultDevice();
// allocate Buffer
NSUInteger BufferLength = 100;
id<MTLBuffer> m_Buffer = [m_Device newBufferWithLength:BufferLength options:0]; 

// allocate Texture
MTLTextureDescriptor *shadowTextureDesc = [MTLTextureDescriptor texture2DDescriptorWithPixelFormat: MTLPixelFormatDepth32Float width: 1024 height: 1024 mipmapped: NO];
id<MTLTexture> m_Texture = [m_Device newTextureWithDescriptor:shadowTextureDesc];

// release Buffer
[m_Buffer setPurgeableState:MTLPurgeableStateEmpty]; 
[m_Buffer release];

// release Texture
[m_Texture setPurgeableState:MTLPurgeableStateEmpty];
[m_Texture release];

About setPurgeableState, you can refer to the link(https://developer.apple.com/documentation/metal/mtlresource/1515898-setpurgeablestate)