audiounit_ios: add @autoreleasepool to GetLatency

GetLatency calls [AVAudioSession outputLatency] in the following callstack:

• _malloc_zone_malloc_instrumented_or_legacy
• _Block_copy
• -[_NSXPCDistantObject _initWithConnection:proxyNumber:generationCount:interface:options:error:]
• -[NSXPCConnection synchronousRemoteObjectProxyWithErrorHandler:]
• caulk::xpc::message<id __strong, objc_object* __strong, unsigned int>::sync_proxy()
• GetPropertyXPC(std::__1::shared_ptras::client::XPCConnection, unsigned int, NSString*, bool)
• GetProperty(AVAudioSessionImpl*, NSString*, bool)
• float GetProperty_DefaultToZeroXPC(AVAudioSessionImpl*, NSString*, bool)
• -[AVAudioSession outputLatency]
• GetLatency
• GetLatency
• ca_Render
• RenderCallback
• ausdk::AUInputElement::PullInput(unsigned int&, AudioTimeStamp const&, unsigned int, unsigned int)
• AUInputFormatConverter2::InputProc(OpaqueAudioConverter*, unsigned int*, AudioBufferList*, AudioStreamPacketDescription**, void*)
• caulk::expected<unsigned int, int> caulk::function_ref<caulk::expected<unsigned int, int> (ACAudioSpan&)>::functor_invoker<acv2::AudioConverterV2::fillComplexBuffer(int ()(OpaqueAudioConverter, unsigned int*, AudioBufferList*, AudioStreamPacketDescription**, void*), void*, unsigned int*, AudioBufferList*, AudioStreamPacketDescription*, AudioStreamPacketDependencyInfo*)::$_2>(caulk::details::erased_callable<caulk::expected<unsigned int, int> (ACAudioSpan&)> const&, ACAudioSpan&)
• acv2::AudioConverterChain::ObtainInput(acv2::AudioConverterBase&, unsigned int)
• acv2::CBRConverter::ProduceOutput(ACAudioSpan&)
• acv2::AudioConverterChain::ProduceOutput(caulk::function_ref<caulk::expected<unsigned int, int> (ACAudioSpan&)>, ACBaseAudioSpan&)
• acv2::AudioConverterV2::fillComplexBuffer(int ()(OpaqueAudioConverter, unsigned int*, AudioBufferList*, AudioStreamPacketDescription**, void*), void*, unsigned int*, AudioBufferList*, AudioStreamPacketDescription*, AudioStreamPacketDependencyInfo*)
• with_resolved(OpaqueAudioConverter*, caulk::function_ref<int (AudioConverterAPI*)>)
• AudioConverterFillComplexBuffer
• AUConverterBase::RenderBus(unsigned int&, AudioTimeStamp const&, unsigned int, unsigned int)
• AURemoteIO::RenderBus(unsigned int&, AudioTimeStamp const&, unsigned int, unsigned int)
• ausdk::AUBase::DoRender(unsigned int&, AudioTimeStamp const&, unsigned int, unsigned int, AudioBufferList&)
• AURemoteIO::PerformIO(unsigned int, unsigned int, unsigned int, AudioTimeStamp const&, AudioTimeStamp const&, AudioBufferList const*, AudioBufferList*, int&)
• _XPerformIO
• mshMIGPerform
• MSHMIGDispatchMessage
• void* caulk::thread_proxy<std::__1::tuple<caulk::thread::attributes, AURemoteIO::IOThread::IOThread(AURemoteIO&, caulk::thread::attributes const&, caulk::mach::os_workgroup_managed const&)::'lambda'(), std::__1::tuple<>>>(void*)
• _pthread_start
• thread_start

The call to Objective-C function might generate objects released from autoreleasepool, which seems to be the case with the call to [NSXPConnection synchronousRemoteObjectProxyWithErrorHandler]¹.

I've not found where exactly [[block copy] autorelease] was called but setting up the autoreleasepool before unwinding back to the C code removes the accumulatoin of memory on this specify callstack.

1. https://developer.apple.com/documentation/foundation/nsxpcconnection/2879410-synchronousremoteobjectproxywith?language=objc ↩