lldb --batch -k bt -k 'exit 123' -o run -o run -o run -o run -o run -o run -o run -o run -o run -o run -o run -o run -o run -o run -o run -o run -o run -o run -o run  ./repro

swiftc repro.swift && lldb --batch -k bt -k "exit 123" $(for f in $(seq 50); do echo -o run; done) ./repro

$ docker run -it --rm --privileged -v "$PWD:$PWD" -w "$PWD" swift:5.5-focal bash -c 'swiftc repro.swift && lldb --batch -k bt -k "exit 123" $(for f in $(seq 50); do echo -o run; done) ./repro'
(lldb) target create "./repro"
Current executable set to '/tmp/repro' (x86_64).
(lldb) run
Process 47 exited with status = 0 (0x00000000) 

[...]

Process 1433 launched: '/tmp/repro' (x86_64)
(lldb) run
Process 1499 exited with status = 0 (0x00000000) 

Process 1499 launched: '/tmp/repro' (x86_64)
(lldb) run
Process 1565 stopped
* thread #​53, name = 'repro', stop reason = signal SIGSEGV: invalid address (fault address: 0xfffffffffffffff8)
    frame #​0: 0x00007ffff7bcf9dd libswiftCore.so`Swift._ContiguousArrayStorage.__deallocating_deinit + 13
libswiftCore.so`Swift._ContiguousArrayStorage.__deallocating_deinit:
->  0x7ffff7bcf9dd <+13>: movq   -0x8(%rdx), %rax
    0x7ffff7bcf9e1 <+17>: movzbl 0x50(%rax), %edi
    0x7ffff7bcf9e5 <+21>: leal   0x20(%rdi), %eax
    0x7ffff7bcf9e8 <+24>: notl   %edi
Target 0: (repro) stopped.

Process 1565 launched: '/tmp/repro' (x86_64)
(lldb) run
Process 1565 exited with status = 9 (0x00000009) 
Process 1631 exited with status = 0 (0x00000000) 

Process 1631 launched: '/tmp/repro' (x86_64)

import Foundation
import Dispatch

let threads = 60
let sem1 = DispatchSemaphore(value: 0)
let sem2 = DispatchSemaphore(value: 0)
let g = DispatchGroup()

(0..<threads).forEach { index in
    DispatchQueue(label: "\(index)").async(group: g) {
        sem1.signal()
        // All threads should be parked here
        sem2.wait()
        precondition(ProcessInfo.processInfo.hostName.utf8.count > 0)
    }
}

(0..<threads).forEach { index in
    sem1.wait()
}
(0..<threads).forEach { index in
    sem2.signal()
}
g.wait()