I'm working on an FFI for working with ObjectiveC/Foundation/Metal. AFAIU, as many APIs create and autorelease objects, I need to ensure that an NSAutoreleasePool is active when calling into these APIs. So I've created a wrapper that basically mimics @autoreleasepool by creating and initializing an NSAutoreleasePool, running some code, and then draining the pool. So far so good; I'm using this functionality around most of my entry points into the ObjectiveC world. There's two issues I don't understand though. The first is that NSAutoreleasePool initialization seems to require an active autorelease pool, which seems like a chicken-and-egg problem. Running with OBJC_DEBUG_MISSING_POOLS=YES and breaking on objc_autoreleaseNoPool, I see: objc[30336]: MISSING POOLS: (0x1e2e89c40) Object 0x6000007e0050 of class __NSCFString autoreleased with no pool in place - just leaking - break on objc_autoreleaseNoPool() to debug (lldb) bt objc_autoreleaseNoPool at /usr/lib/libobjc.A.dylib (unknown line) _ZN19AutoreleasePoolPage17autoreleaseNoPageEP11objc_object at /usr/lib/libobjc.A.dylib (unknown line) _ZN19AutoreleasePoolPage4pushEv at /usr/lib/libobjc.A.dylib (unknown line) _CFAutoreleasePoolPush at /System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation (unknown line) -[NSAutoreleasePool init] at /System/Library/Frameworks/Foundation.framework/Versions/C/Foundation (unknown line) macro expansion at /Users/tim/Julia/pkg/ObjectiveC/src/syntax.jl:163 [inlined] NSAutoreleasePool at /Users/tim/Julia/pkg/ObjectiveC/src/foundation.jl:427 The second, related problem is that some APIs that are called by Metal from a background thread I don't control: (lldb) bt * thread #11, queue = 'com.Metal.CompletionQueueDispatch', stop reason = breakpoint 1.1 * frame #0: 0x000000018c21b9e8 libobjc.A.dylib`objc_autoreleaseNoPool frame #1: 0x000000018c1eb99c libobjc.A.dylib`AutoreleasePoolPage::autoreleaseNoPage(objc_object*) + 252 frame #2: 0x000000018c21c9ec libobjc.A.dylib`AutoreleasePoolPage::push() + 76 frame #3: 0x00000001aaef9694 IOGPU`-[IOGPUMetalBuffer dealloc] + 104 frame #4: 0x00000001f83554e4 AGXMetalG15X_B0`-[AGXBuffer dealloc] + 44 frame #5: 0x00000001f837eb98 AGXMetalG15X_B0`-[AGXG15XFamilyBuffer dealloc] + 76 frame #6: 0x000000019687c1c4 Metal`MTLResourceListChunkFreeEntries(MTLResourceListChunk*) + 64 frame #7: 0x000000019674e2b0 Metal`-[MTLResourceList releaseAllObjectsAndReset] + 72 frame #8: 0x00000001aaefbd10 IOGPU`IOGPUMetalCommandBufferStorageReset + 36 frame #9: 0x00000001aaefbcac IOGPU`IOGPUMetalCommandBufferStorageDealloc + 76 frame #10: 0x00000001aaefa130 IOGPU`-[IOGPUMetalCommandBuffer didCompleteWithStartTime:endTime:error:] + 240 frame #11: 0x000000019674dce4 Metal`-[_MTLCommandQueue commandBufferDidComplete:startTime:completionTime:error:] + 108 frame #12: 0x00000001aaf03b54 IOGPU`IOGPUNotificationQueueDispatchAvailableCompletionNotifications + 128 frame #13: 0x00000001aaf03c60 IOGPU`__IOGPUNotificationQueueSetDispatchQueue_block_invoke + 64 frame #14: 0x000000018c4049d0 libdispatch.dylib`_dispatch_client_callout4 + 20 frame #15: 0x000000018c420c5c libdispatch.dylib`_dispatch_mach_msg_invoke + 468 frame #16: 0x000000018c40bd28 libdispatch.dylib`_dispatch_lane_serial_drain + 368 frame #17: 0x000000018c421998 libdispatch.dylib`_dispatch_mach_invoke + 444 frame #18: 0x000000018c40bd28 libdispatch.dylib`_dispatch_lane_serial_drain + 368 frame #19: 0x000000018c40ca08 libdispatch.dylib`_dispatch_lane_invoke + 432 frame #20: 0x000000018c40bd28 libdispatch.dylib`_dispatch_lane_serial_drain + 368 frame #21: 0x000000018c40c9d4 libdispatch.dylib`_dispatch_lane_invoke + 380 frame #22: 0x000000018c41761c libdispatch.dylib`_dispatch_root_queue_drain_deferred_wlh + 288 frame #23: 0x000000018c416e90 libdispatch.dylib`_dispatch_workloop_worker_thread + 404 frame #24: 0x000000018c5b2114 libsystem_pthread.dylib`_pthread_wqthread + 288 (lldb) c Process 26902 resuming objc[26902]: MISSING POOLS: (0x1e2e89c40) Object 0x14c8a2400 of class AGXG15SDevice autoreleased with no pool in place - just leaking - break on objc_autoreleaseNoPool() to debug Again, I'm not sure how I'm supposed to run this under an autorelease pool.

I'm running into an issue with threadgroup memory where data written to it seemingly gets lost when I use int8_t or int16_t element types: #include <metal_stdlib> using namespace metal; kernel void kernel_function(device int16_t* R, uint index [[thread_position_in_threadgroup]]) { threadgroup int16_t shared[1]; shared[index] = (int16_t) 42; threadgroup_barrier(mem_flags::mem_threadgroup); R[0] = shared[index]; } If I execute this kernel (using the following host code: https://gist.github.com/maleadt/ffcda8fc94f03f32347c3167ccca70a8 ), I get zeros in my output buffer. If I change the element type from int16_t to int32_t (just find/replace in the kernel and host code) I get the expected results. I'm new to Metal, so I guess I'm doing something wrong here. I'm using an M1 Pro on Monterey, with Xcode 13.4.1. EDIT: interestingly, running under MTL_SHADER_VALIDATION=1 results in the expected output, so this does start to look like a miscompilation in the back-end.