Performing calculations on a GPU

At a glance

Project structure

Source bundle/
├── MetalComputeBasic/
│   ├── main.m
│   ├── MetalAdder.h
│   ├── MetalAdder.m
│   └── add.metal
├── Configuration/
│   └── SampleCode.xcconfig
└── MetalComputeBasic.xcodeproj/
    ├── .xcodesamplecode.plist
    └── project.pbxproj

Structure observations

• Architecturally prominent files are ranked from entry points and role-named declarations; resource-only paths are omitted.
• Primary languages: C/Objective-C header, Metal, Objective-C.
• The verified tree contains 3 project/configuration file(s) and 1 source declaration(s).

Overall architecture

flowchart LR
    N1["main"]
    N2["Metal / metal_stdlib APIs"]
    N1 --> N2

Reference code

MetalComputeBasic/main.m:25 — architecture anchor

int main(int argc, const char * argv[]) {
    @autoreleasepool {

        id<MTLDevice> device = MTLCreateSystemDefaultDevice();

        // Create the custom object used to encapsulate the Metal code.
        // Initializes objects to communicate with the GPU.
        MetalAdder* adder = [[MetalAdder alloc] initWithDevice:device];

        // Create buffers to hold data
        [adder prepareData];

        // Send a command to the GPU to perform the calculation.
        [adder sendComputeCommand];

        NSLog(@"Execution finished");
    }
    return 0;
}

Interpretation

The arrows summarize the source-visible entry, role-named types or folders, and framework direction; when nodes come from structural folders, the sequence is a high-level interpretation rather than proof that every adjacent node calls the next. Ownership is claimed only where the next section cites a stored property or assignment. The diagram is intentionally limited to the dominant path into Metal.

Ownership and state

classDiagram
    main --> MetalAPIs : uses

Ownership evidence

MetalComputeBasic/MetalAdder.h:11 — stored dependency or nearest verified ownership anchor

NS_ASSUME_NONNULL_BEGIN

Composition arrows indicate a source-visible construction expression or locally owned value state; aggregation means the owner stores or receives a dependency without proving exclusive lifetime ownership.

Concurrency, scheduling, and thread safety

Evidence limit: actor isolation, async/await, or Task creation does not by itself prove background-thread execution; Sendable conformance alone does not prove thread-safe mutation.

No source-visible execution, scheduling, or synchronization boundary was found in the indexed source.

@MainActor/MainActor.run, DispatchQueue.main, and RunLoop.main are reported as distinct isolation, queue, and event-loop mechanisms. A plain Task is kept separate from Task.detached; neither is labeled as a background thread.

State propagation, frameworks, and dependencies

Evidence limit: an import proves a source-level compilation dependency at the cited line; it does not prove runtime use, architectural adoption, or whether a Swift package is a direct application dependency.

receive(on:) describes downstream delivery scheduling, while subscribe(on:) describes upstream subscription/request/cancel scheduling. An import Combine alone establishes neither behavior nor a Store, reducer, Redux, or other application architecture.

Class and protocol design

MetalComputeBasic/MetalAdder.h:13 — representative type boundary

@interface MetalAdder : NSObject
- (instancetype) initWithDevice: (id<MTLDevice>) device;
- (void) prepareData;
- (void) sendComputeCommand;
@end

No local protocol conformance is claimed as protocol-oriented design; external framework conformances are listed only as dependencies.

Access control

Reference code

MetalComputeBasic/MetalAdder.h:13 — representative boundary

@interface MetalAdder : NSObject
- (instancetype) initWithDevice: (id<MTLDevice>) device;
- (void) prepareData;
- (void) sendComputeCommand;
@end

Swift declarations without a modifier are internal; explicit private, fileprivate, private(set), public, or open entries above are interpreted by language semantics. Objective-C/C samples instead rely on header and implementation boundaries, which are not equivalent to Swift lexical privacy.

Logic ownership and placement

Design patterns

Main application flow

sequenceDiagram
    participant MetalAdder
    participant _mCommandQueue
    participant commandBuffer
    participant computeEncoder
    MetalAdder->>_mCommandQueue: commandBuffer()
    MetalAdder->>commandBuffer: computeCommandEncoder()
    MetalAdder->>MetalAdder: encodeAddCommand()
    MetalAdder->>computeEncoder: endEncoding()
    MetalAdder->>commandBuffer: commit()
    MetalAdder->>commandBuffer: waitUntilCompleted()
    MetalAdder->>MetalAdder: verifyResults()

Reference code

MetalComputeBasic/MetalAdder.m:105 — sendComputeCommand()

- (void) sendComputeCommand
{
    // Create a command buffer to hold commands.
    id<MTLCommandBuffer> commandBuffer = [_mCommandQueue commandBuffer];
    assert(commandBuffer != nil);

    // Start a compute pass.
    id<MTLComputeCommandEncoder> computeEncoder = [commandBuffer computeCommandEncoder];
    assert(computeEncoder != nil);

    [self encodeAddCommand:computeEncoder];

    // End the compute pass.
    [computeEncoder endEncoding];

    // Execute the command.
    [commandBuffer commit];

    // Normally, you want to do other work in your app while the GPU is running,
    // but in this example, the code simply blocks until the calculation is complete.
    [commandBuffer waitUntilCompleted];

    [self verifyResults];
}

Naming conventions

• Types: feature-specific names rather than reusable layer suffixes.
• Protocols: no local protocol declaration in the scanned source.
• Methods: initWithDevice, prepareData, sendComputeCommand, encodeAddCommand, generateRandomFloatData, verifyResults.
• Files: MetalComputeBasic/MetalAdder.h, MetalComputeBasic/MetalAdder.m.

Architecture takeaways

• main is the main source-visible entry or composition anchor for this sample.
• Framework work reaches Metal, metal_stdlib through a deliberately small high-level chain; the detailed API graph remains inside the cited implementation files.
• Stored-property evidence identifies lifecycle collaboration; it does not by itself prove exclusive object ownership.
• Access-control conclusions separate verified language visibility from the likely design rationale.
• The source does not justify labeling the design protocol-oriented.

Source map

• Official Apple documentation