I have a sandboxed Mac app which I can grant access to a folder using an NSOpenPanel. Once it’s been granted access it can enumerate the contents of the folder just fine. If I rename the folder while the app is open and then make the app enumerate the folder’s contents again, though, it seems to have lost access. What’s the recommended way to have an app’s sandbox “track” files as they’re moved around the filesystem? (NSDocument handles this for you, from what I can tell.) I’ve managed to hack something together with a combination of Dispatch sources and security-scoped bookmarks, but it feels like there must be an easier solution …

I’ve been experimenting with Dispatch, and workloops in particular. I gather that they’re similar to serial queues, except that they reorder work items by QoS. I suspect there’s more to workloops than meets the eye, though; calling dispatch_set_target_queue on them has no effect, in spite of the <dispatch/workloop.h> saying that workloops “can be passed to all APIs accepting a dispatch queue, except for functions from the dispatch_sync() family”. Workloops keep showing up in odd places like Metal and Network.framework backtraces, and <dispatch/workloop.h> includes functionality for tying workloops to os_workgroups (?!). What exactly is a workloop beyond just a serial queue with priority ordering, and why can’t I set the target queue of one?

Suppose I want to draw a red rectangle onto my render target using a compute shader. id<MTLComputeCommandEncoder> encoder = [commandBuffer computeCommandEncoder]; [encoder setComputePipelineState:pipelineState]; simd_ushort2 position = simd_make_ushort2(100, 100); simd_ushort2 size = simd_make_ushort2(50, 50); [encoder setBytes:&position length:sizeof(position) atIndex:0]; [encoder setTexture:drawable.texture atIndex:0]; [encoder dispatchThreads:MTLSizeMake(size.x, size.y, 1) threadsPerThreadgroup:MTLSizeMake(32, 32, 1)]; [encoder endEncoding]; #include <metal_stdlib> using namespace metal; kernel void Compute(ushort2 position_in_grid [[thread_position_in_grid]], constant ushort2 &position, texture2d<half, access::write> texture) { texture.write(half4(1, 0, 0, 1), position_in_grid + position); } This works just fine: Now, say for whatever reason I want to start using imageblocks in my compute kernel. First, I set the imageblock size on the CPU side: id<MTLComputeCommandEncoder> encoder = [commandBuffer computeCommandEncoder]; [encoder setComputePipelineState:pipelineState]; MTLSize threadgroupSize = MTLSizeMake(32, 32, 1); [encoder setImageblockWidth:threadgroupSize.width height:threadgroupSize.height]; simd_ushort2 position = simd_make_ushort2(100, 100); simd_ushort2 size = simd_make_ushort2(50, 50); [encoder setBytes:&position length:sizeof(position) atIndex:0]; [encoder setTexture:drawable.texture atIndex:0]; MTLSize gridSize = MTLSizeMake(size.x, size.y, 1); [encoder dispatchThreads:gridSize threadsPerThreadgroup:threadgroupSize]; And then I update the compute kernel to simply declare the imageblock – note I never actually read from or write to it: #include <metal_stdlib> using namespace metal; struct Foo { int foo; }; kernel void Compute(ushort2 position_in_grid [[thread_position_in_grid]], constant ushort2 &position, texture2d<half, access::write> texture, imageblock<Foo> imageblock) { texture.write(half4(1, 0, 0, 1), position_in_grid + position); } And now out of nowhere Metal’s shader validation starts complaining about mismatched texture usage flags: 2024-06-22 00:57:15.663132+1000 TextureUsage[80558:4539093] [GPUDebug] Texture usage flags mismatch executing kernel function "Compute" encoder: "1", dispatch: 0 2024-06-22 00:57:15.672004+1000 TextureUsage[80558:4539093] [GPUDebug] Texture usage flags mismatch executing kernel function "Compute" encoder: "1", dispatch: 0 2024-06-22 00:57:15.682422+1000 TextureUsage[80558:4539093] [GPUDebug] Texture usage flags mismatch executing kernel function "Compute" encoder: "1", dispatch: 0 2024-06-22 00:57:15.687587+1000 TextureUsage[80558:4539093] [GPUDebug] Texture usage flags mismatch executing kernel function "Compute" encoder: "1", dispatch: 0 2024-06-22 00:57:15.698106+1000 TextureUsage[80558:4539093] [GPUDebug] Texture usage flags mismatch executing kernel function "Compute" encoder: "1", dispatch: 0 The texture I’m writing to comes from a CAMetalDrawable whose associated CAMetalLayer has framebufferOnly set to NO. What am I missing?