RunLoop.run hang in containerized Linux

Using Swift
1

I'm experiencing RunLoop.run hanging on ppol in a containerized Linux environment. Swift version doesn't appear to be a factor (I tried as far back as 5.8). It's such a basic example, I'm suprised it's not working and that I must be missing something obvious. Does this example hang for anyone else?

FROM swift:latest
WORKDIR /workspace
RUN swift package init --name Example --type executable
RUN echo "import Foundation" > Sources/main.swift
RUN echo "print(\"BEGIN\")" >> Sources/main.swift
RUN echo "RunLoop.current.run(until: Date(timeIntervalSinceNow: 1))" >> Sources/main.swift
RUN echo "print(\"END\")" >> Sources/main.swift
RUN swift build
ENTRYPOINT [".build/debug/Example"]

Output:

BEGIN
<hang>

Thread dump:

* thread #1, name = 'RunLoopHang', stop reason = signal SIGSTOP
  * frame #0: 0x0000ffff94d210c8 libc.so.6`ppoll + 184
    frame #1: 0x0000ffff95bc1740 libFoundation.so`__CFRunLoopServiceFileDescriptors + 104
    frame #2: 0x0000ffff95bbd524 libFoundation.so`__CFRunLoopRun + 1016
    frame #3: 0x0000ffff95bbceac libFoundation.so`CFRunLoopRunSpecific + 476
    frame #4: 0x0000ffff95b44d44 libFoundation.so`Foundation.RunLoop.run(until: FoundationEssentials.Date) -> () + 156
    frame #5: 0x0000aaaac2ec10f0 RunLoopHang`RunLoopHang_main at main.swift:3:17
    frame #6: 0x0000ffff94c684c4 libc.so.6`___lldb_unnamed_symbol3097 + 116
    frame #7: 0x0000ffff94c68598 libc.so.6`__libc_start_main + 152
    frame #8: 0x0000aaaac2ec0cf0 RunLoopHang`_start + 48
  thread #2, name = 'RunLoopHang', stop reason = signal SIGSTOP
    frame #0: 0x0000ffff94d2bd74 libc.so.6`epoll_pwait + 148
    frame #1: 0x0000ffff95efd024 libdispatch.so`_dispatch_event_loop_drain + 64
    frame #2: 0x0000ffff95ef1fdc libdispatch.so`_dispatch_mgr_invoke + 124
    frame #3: 0x0000ffff95ef1f50 libdispatch.so`_dispatch_mgr_thread + 132
    frame #4: 0x0000ffff95ef578c libdispatch.so`_dispatch_worker_thread + 432
    frame #5: 0x0000ffff94cc597c libc.so.6`___lldb_unnamed_symbol3477 + 892
    frame #6: 0x0000ffff94d2ba4c libc.so.6`___lldb_unnamed_symbol3850 + 12

Docker version 27.4.0, build bde2b89
macOS 15.2
2

Works for me, although I'm using Orbstack:

❯ docker build -t dtest -f Dockerfile .
[+] Building 50.8s (12/12) FINISHED                                                                        docker:orbstack
 => [internal] load build definition from Dockerfile                                                                  0.0s
 => => transferring dockerfile: 423B                                                                                  0.0s
 => [internal] load metadata for docker.io/library/swift:latest                                                       2.9s
 => [internal] load .dockerignore                                                                                     0.0s
 => => transferring context: 2B                                                                                       0.0s
 => [1/8] FROM docker.io/library/swift:latest@sha256:816ca4a42c1ab5e3993060f8e8bbc80cf88ac82d7ad52ded90b814ab79def8  42.8s
 => => resolve docker.io/library/swift:latest@sha256:816ca4a42c1ab5e3993060f8e8bbc80cf88ac82d7ad52ded90b814ab79def8a  0.0s
 => => sha256:816ca4a42c1ab5e3993060f8e8bbc80cf88ac82d7ad52ded90b814ab79def8ad 2.62kB / 2.62kB                        0.0s
 => => sha256:f5e223ed75fc01e11b6ec5a2f8c337b51121f9eef06c4a50eace4ea873f9e47e 1.73kB / 1.73kB                        0.0s
 => => sha256:69fba260c0ad349a57791f941bf88edee6c75fe0b8501a3de756656dae4e3703 5.72kB / 5.72kB                        0.0s
 => => extracting da0a385c983f                                                                                        8.7s
 => => extracting 8ef7323a9954                                                                                        0.0s
 => [2/8] WORKDIR /workspace                                                                                          0.3s
 => [3/8] RUN swift package init --name Example --type executable                                                     0.4s
 => [4/8] RUN echo "import Foundation" > Sources/main.swift                                                           0.1s
 => [5/8] RUN echo "print("BEGIN")" >> Sources/main.swift                                                             0.1s
 => [6/8] RUN echo "RunLoop.current.run(until: Date(timeIntervalSinceNow: 1))" >> Sources/main.swift                  0.1s
 => [7/8] RUN echo "print("END")" >> Sources/main.swift                                                               0.1s
 => [8/8] RUN swift build                                                                                             3.7s
 => exporting to image                                                                                                0.1s
 => => exporting layers                                                                                               0.1s
 => => writing image sha256:fb21e7005d8317e791011877d78e77a4019969d0bcc12fe87669da3577c5ed01                          0.0s
 => => naming to docker.io/library/dtest                                                                              0.0s
~/Downloads took 51s
❯ docker run --rm dtest
BEGIN
END

System info:

❯ sw_vers
ProductName:            macOS
ProductVersion:         15.2
BuildVersion:           24C101

Orbstack Version 1.9.2 (18814)

3

Thanks for trying it. OrbStack is also working as expected for me. I'll report this to the Docker team.

1 Like