Exit tests hang indefinitely on Ubuntu 20.04

[jmschonfeld]

Description

When adding an exit test to a test suite, that test hangs indefinitely when run on Ubuntu 20.04. The test runs successfully and completes in ~0.3s on Ubuntu 22.04 and on all of the macOS versions that I've tried.

Reproduction

1. Download the latest nightly-focal swift docker image
2. Create a project that includes the following unit test

@Test func testExits() {
    await #expect(processExitsWith: .failure) {
        fatalError("I crashed")
    }
}

3. Build and run the test (swift test)
4. Notice that the test hangs indefinitely after ◇ Test testExits() started.

Expected behavior

Exit tests complete successfully on all supported platforms

Environment

↳ Testing Library Version: 6.3-dev (d6111205ce07f17)
↳ Target Platform: aarch64-unknown-linux-gnu

Swift version 6.2-dev (LLVM 5e7837820b1c886, Swift d5ef256b402bff7)
Target: aarch64-unknown-linux-gnu
Build config: +assertions

Linux nightly-focal 6.1.68 #1 SMP Fri Nov 22 18:05:17 UTC 2024 aarch64 aarch64 aarch64 GNU/Linux

Additional information

This is blocking Foundation from adopting exit tests as swift toolchain CI runs on Ubuntu 20.04

[jmschonfeld]

Here is a sample of the parent and child process while it is hanging:

root@nightly-focal:/Repos# ps -ef | grep swift-foundation
root      4895  4846  0 20:43 pts/0    00:00:00 /Repos/Public/swift-foundation/.build/aarch64-unknown-linux-gnu/debug/swift-foundationPackageTests.xctest --filter testExits --testing-library swift-testing
root      4904  4895  0 20:43 pts/0    00:00:00 /Repos/Public/swift-foundation/.build/aarch64-unknown-linux-gnu/debug/swift-foundationPackageTests.xctest --testing-library swift-testing
root      4915  4032  0 20:43 pts/1    00:00:00 grep --color=auto swift-foundation
root@nightly-focal:/Repos# eu-stack -id -p 4895          
PID 4895 - process
TID 4895:
#0  0x0000ffff8f7f916c __GI___sigsuspend
#1  0x0000ffff90519558 _dispatch_sigsuspend
#2  0x0000ffff90516e70 _dispatch_sig_thread
#3  0x0000ffff8fb5c3c0 __nptl_deallocate_tsd
#4  0x0000ffff8f7e5e54 __libc_start_main
#5  0x0000aaaae46d6d50 $x
#6  0x0000aaaae46d6d50 $x
eu-stack: dwfl_thread_getframes tid 4895 at 0xaaaae46d6d4f in /Repos/Public/swift-foundation/.build/aarch64-unknown-linux-gnu/debug/swift-foundationPackageTests.xctest: no matching address range
TID 4899:
#0  0x0000ffff8f888dc0 __GI___libc_read
#1  0x0000ffff8f888dc0 __GI___libc_read
#2  0x0000ffff8f83618c _IO_new_file_underflow
#3  0x0000ffff8f835298 __GI__IO_file_xsgetn
#4  0x0000ffff8f8292a0 __GI__IO_fread
#5  0x0000ffff8fd33c10 $s7Testing10FileHandleV9readToEndSays5UInt8VGyKF
#6  0x0000ffff8fcbf74c $s7Testing8ExitTestV15_processRecords33_95876674CE05CFF8D0FD5F064E685A97LL15fromBackChannelyAA10FileHandleV_tFZTf4nd_n
#7  0x0000ffff8fcbd2ac $s7Testing8ExitTestV20handlerForEntryPointAC6ResultVACYaYbKcyFZ6resultL_yAfCYaYbKFAFScgyyAFzYbcSgs5Error_pGzYaKXEfU0_AHyYacfU6_TY0_
#8  0x0000ffff90f69fe8 swift::runJobInEstablishedExecutorContext(swift::Job*)
#9  0x0000ffff90f6ad38 swift_job_run
#10 0x0000ffff9050fc70 _dispatch_continuation_pop
#11 0x0000ffff9050faac _dispatch_async_redirect_invoke
#12 0x0000ffff9051930c _dispatch_worker_thread
#13 0x0000ffff8fb5c624 start_thread
#14 0x0000ffff8f89666c thread_start
TID 4900:
#0  0x0000ffff8f896794 __GI_epoll_pwait
#1  0x0000ffff90520bd4 _dispatch_event_loop_drain
#2  0x0000ffff9051602c _dispatch_mgr_invoke
#3  0x0000ffff90515fa0 _dispatch_mgr_thread
#4  0x0000ffff9051930c _dispatch_worker_thread
#5  0x0000ffff8fb5c624 start_thread
#6  0x0000ffff8f89666c thread_start
TID 4905:
#0  0x0000ffff8f868d28 __waitid
#1  0x0000ffff8fcc1f2c $s7Testing17_createWaitThread33_F6EF36D824EB298AB893AA9AF261F249LLytvpfiyyXEfU_15waitForAnyChildL_yyF
#2  0x0000ffff8fcc2214 $s7Testing17_createWaitThread33_F6EF36D824EB298AB893AA9AF261F249LLytvpfiyyXEfU_SvSgADcfU_To
#3  0x0000ffff8fb5c624 start_thread
#4  0x0000ffff8f89666c thread_start
root@nightly-focal:/Repos# eu-stack -id -p 4904
PID 4904 - process
TID 4904:
#0  0x0000ffffb5d6016c __GI___sigsuspend
#1  0x0000ffffb6a73558 _dispatch_sigsuspend
#2  0x0000ffffb6a70e70 _dispatch_sig_thread
#3  0x0000ffffb60c33c0 __nptl_deallocate_tsd
#4  0x0000ffffb5d4ce54 __libc_start_main
#5  0x0000aaaad2cd6d50 $x
#6  0x0000aaaad2cd6d50 $x
eu-stack: dwfl_thread_getframes tid 4904 at 0xaaaad2cd6d4f in /Repos/Public/swift-foundation/.build/aarch64-unknown-linux-gnu/debug/swift-foundationPackageTests.xctest: no matching address range
TID 4907:
#0  0x0000ffffb5defdc0 __GI___libc_read
#1  0x0000ffffb5defdc0 __GI___libc_read
#2  0x0000ffffb5d9d18c _IO_new_file_underflow
#3  0x0000ffffb5d9c298 __GI__IO_file_xsgetn
#4  0x0000ffffb5d902a0 __GI__IO_fread
#5  0x0000ffffb692cc10 $s7Testing10FileHandleV9readToEndSays5UInt8VGyKF
#6  0x0000ffffb68b3f78 $s7Testing8ExitTestV34_decodeCapturedValuesForEntryPoint33_95876674CE05CFF8D0FD5F064E685A97LLyyKF
#7  0x0000ffffb68b3e74 $s7Testing8ExitTestV30findInEnvironmentForEntryPointACSgyFZyACzYaYbKcfU2_yyYaKXEfU_TY0_
#8  0x0000ffffb6dc3fe8 swift::runJobInEstablishedExecutorContext(swift::Job*)
#9  0x0000ffffb6dc4d38 swift_job_run
#10 0x0000ffffb6a69c70 _dispatch_continuation_pop
#11 0x0000ffffb6a69aac _dispatch_async_redirect_invoke
#12 0x0000ffffb6a7330c _dispatch_worker_thread
#13 0x0000ffffb60c3624 start_thread
#14 0x0000ffffb5dfd66c thread_start
TID 4908:
#0  0x0000ffffb5dfd794 __GI_epoll_pwait
#1  0x0000ffffb6a7abd4 _dispatch_event_loop_drain
#2  0x0000ffffb6a7002c _dispatch_mgr_invoke
#3  0x0000ffffb6a6ffa0 _dispatch_mgr_thread
#4  0x0000ffffb6a7330c _dispatch_worker_thread
#5  0x0000ffffb60c3624 start_thread
#6  0x0000ffffb5dfd66c thread_start

[jmschonfeld]

Also attaching the output of strace -f /Repos/Public/swift-foundation/.build/aarch64-unknown-linux-gnu/debug/swift-foundationPackageTests.xctest --filter testExits --testing-library swift-testing. This is all of the output until the end where it just starts repeating the epoll_pwait calls repeatedly/indefinitely

strace.txt

[jmschonfeld]

Also confirmed that this behaves as expected on Ubuntu 24.04