# RunLoop.run hang in containerized Linux **URL:** \ **Category:** Using Swift\ **Created:** [December 24, 2024, 6:32pm UTC](https://forums.swift.org/t/runloop-run-hang-in-containerized-linux/76837 "2024-12-24T18:32:45Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![ileitch](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/ileitch/32/2095_2.png) [@ileitch](https://forums.swift.org/u/ileitch)\ **Post date:** [December 24, 2024, 6:32pm UTC](https://forums.swift.org/t/runloop-run-hang-in-containerized-linux/76837/1 "2024-12-24T18:32:45Z")
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? ```swift 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: ```swift BEGIN ``` Thread dump: ```swift * 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 ``` ```swift Docker version 27.4.0, build bde2b89 macOS 15.2 ``` ---
**Author:** ![finestructure](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/finestructure/32/34879_2.png) [@finestructure](https://forums.swift.org/u/finestructure)\ **Post date:** [December 25, 2024, 3:55pm UTC](https://forums.swift.org/t/runloop-run-hang-in-containerized-linux/76837/2 "2024-12-25T15:55:36Z")
Works for me, although I'm using Orbstack: ```swift ❯ 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: ```swift ❯ sw_vers ProductName: macOS ProductVersion: 15.2 BuildVersion: 24C101 ``` Orbstack Version 1.9.2 (18814) > **[OrbStack · Fast, light, simple Docker & Linux](https://orbstack.dev)** > > Say goodbye to slow, clunky containers and VMs. The fast, light, and easy way to run containers and Linux. Develop at lightspeed with our Docker Desktop alternative. ---
**Author:** ![ileitch](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/ileitch/32/2095_2.png) [@ileitch](https://forums.swift.org/u/ileitch)\ **Post date:** [December 26, 2024, 11:25am UTC](https://forums.swift.org/t/runloop-run-hang-in-containerized-linux/76837/3 "2024-12-26T11:25:37Z")
Thanks for trying it. OrbStack is also working as expected for me. I'll report this to the Docker team. ---
**Author:** ![lukeh](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/lukeh/32/31648_2.png) [@lukeh](https://forums.swift.org/u/lukeh)\ **Post date:** [September 29, 2025, 5:44pm UTC](https://forums.swift.org/t/runloop-run-hang-in-containerized-linux/76837/4 "2025-09-29T17:44:25Z")
I’m seeing this occasionally, Swift 6.2 on Linux. It appears a similar issue was reported [back in 2017](https://github.com/swiftlang/swift-corelibs-foundation/issues/3869). ```swift (lldb) p fds[0] (pollfd) (fd = 25, events = 1, revents = 0) ``` where FD 25 is: ```swift InfernoUI 196501 lukeh 25u a_inode 0,15 0 66 [eventpoll:8,24,26] ``` which as far as I can tell is an `epoll(7)` file descriptor which in turn references IDs 8, 24 and 26: ```swift InfernoUI 196501 lukeh 8u a_inode 0,15 0 66 [eventfd:281] InfernoUI 196501 lukeh 24u a_inode 0,15 0 66 [eventfd:210] InfernoUI 196501 lukeh 26u a_inode 0,15 0 66 [timerfd] ``` AFAICT the poll FD and event FDs are created by `__CFRunLoopCreate()` and `_dispatch_runloop_queue_handle_init()`, and the timer FD by `__CFRunLoopCopyMode()`. Unfortunately we need to use `CFRunLoop` in order to guarantee that the main thread (in the `pthread`) sense is also the main actor / main dispatch thread, as some third-party libraries we are scheduling need to be called from this. (When using `dispatch_main()`, the first thread is suspended.) Edit: I think this may have been a bug on our end, with an incorrect (too large) value passed to a `CFTimer`.