Internals

Under the hood, metal-rs is powered by three main dependencies.

rust-objc and rust-block and foreign-types.

These dependencies are used to communicate with the Objective-C runtime in order to allocate, de-allocate and call methods on the classes and objects that power Metal applications.

Memory Management

metal-rs follows Apple's memory management policy.

When calling a method such as CaptureManager::shared(), the implementation looks like this:

impl CaptureManager {
    pub fn shared<'a>() -> &'a CaptureManagerRef {
        unsafe {
            let class = class!(MTLCaptureManager);
            msg_send![class, sharedCaptureManager]
        }
    }
}

Note that a borrowed reference is returned. As such, when the returned reference is dropped, memory will not be deallocated.

Contrast this with the StencilDescriptor::new() method.

impl StencilDescriptor {
    pub fn new() -> Self {
        unsafe {
            let class = class!(MTLStencilDescriptor);
            msg_send![class, new]
        }
    }
}

In this case we are calling the new method on a class, which returns an owned object.

The macro

foreign_obj_type! {
    type CType = MTLStencilDescriptor;
    pub struct StencilDescriptor;
    pub struct StencilDescriptorRef;
}

ensures that when the owned StencilDescriptor is dropped it will call release on the backing Objective-C object, leading to the memory being deallocated.