Capturing a noncopyable type in an async closure

taylorswift · October 30, 2023, 12:56am

i got this down to a minimal reproducer which i filed as a bug here:

double free when capturing noncopyable value in async closure

opened 12:55AM - 30 Oct 23 UTC

bug triage needed

the following test program crashes with a double free. ```swift struct TimeC…op:~Copyable, Sendable { final class Class:Sendable { init() { } } let x:Class init() { self.x = .init() } func use() { } deinit { } } @main enum Main { static func main() async throws { do { let cop:TimeCop = .init() async let _:Void = { cop.use() try await Task.sleep(for: .milliseconds(50)) }() } } } ``` ``` $ swiftc -parse-as-library example.swift $ ./example ``` ``` 💣 Program crashed: Bad pointer dereference at 0x0000000000000000 Thread 4 crashed: 0 0x0000000000000000 1 0x00007fcf6be4c29b bool swift::RefCounts<swift::RefCountBitsT<(swift::RefCountInlinedness)1> >::doDecrementSlow<(swift::PerformDeinit)1>(swift::RefCountBitsT<(swift::RefCountInlinedness)1>, unsigned int) + 122 in libswiftCore.so 2 0x00005598a378b9c9 TimeCop.deinit + 24 in example 3 0x00005598a378bcd5 __swift_async_resume_get_context + 36 in example 4 0x00007fcf6be4b8e0 _swift_release_dealloc + 15 in libswiftCore.so 5 0x00007fcf6be4c29b bool swift::RefCounts<swift::RefCountBitsT<(swift::RefCountInlinedness)1> >::doDecrementSlow<(swift::PerformDeinit)1>(swift::RefCountBitsT<(swift::RefCountInlinedness)1>, unsigned int) + 122 in libswiftCore.so 6 0x00005598a378bc2e static Main.main() + 93 in example 7 0x00005598a378c600 static Main.$main() in example ``` ``` $ swift --version Swift version 5.9.1 (swift-5.9.1-RELEASE) Target: x86_64-unknown-linux-gnu ```