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A configured upload command inherits cmux's blocked signals and waits out its own timeouts - #12383
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Included review availability: Your plan provides up to 10 included reviews per hour; 0 remain after this review. 📝 WalkthroughWalkthroughSpawned commands and notification hooks now clear inherited signal masks. Custom upload and notification-hook teardown coordinate process-group termination with leader collection. Regression tests cover blocked signals and descendants that outlive their leaders. ChangesProcess teardown behavior
Priority: ⚪ Not assessed Estimated code review effort: 3 (Moderate) | ~25 minutes Change: Bug fix Sequence Diagram(s)sequenceDiagram
participant TerminalCustomUploadRunner
participant SpawnedProcess
participant ProcessGroup
TerminalCustomUploadRunner->>SpawnedProcess: awaitLeaderExit()
SpawnedProcess-->>TerminalCustomUploadRunner: leader exit observed
TerminalCustomUploadRunner->>ProcessGroup: SIGTERM, then SIGKILL
TerminalCustomUploadRunner->>SpawnedProcess: collectLeader()
Merge Risk: ⚪ Minimal · up to No actionable merge-blocking issue is established. The change is ready for normal test and merge checks. Security Architecture ReviewSecurity architecture risk: 🟡 Moderate · up to The change improves child-process cleanup, but concurrent cancellation may briefly allow a signal to reach an unrelated process group. That possibility warrants review, although the window is narrow and its practical exposure is uncertain. Retained concerns
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Full details: Description checkExplanation The description gives a detailed problem statement, implementation explanation, regression-test coverage, and reported results. However, it does not follow the required template structure, lacks the required Demo Video section or attachment for this behavior change, and omits the Checklist. Full details: Cmux Swift Blocking RuntimeExplanation The production diff adds blocking synchronization in Resolution Replace Full details: Cmux Swift Package BoundariesExplanation The production diff materially expands low-level process-supervision logic in the app target. Resolution Extract the shared POSIX process supervision into a small macOS SwiftPM target, such as
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Inline comments:
In `@cmuxTests/TerminalUploadCommandTests.swift`:
- Around line 370-372: Increase the teardown timeout for the
TerminalImageTransferOperation test at both matching test sites, using the same
larger duration so the spawned descendant can record its PID and begin sleeping
before teardown polling starts. Preserve the existing waitForExit process-state
polling behavior.
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Sources/TerminalCustomUploadRunner.swiftSources/TerminalNotificationPolicy.swiftcmuxTests/NotificationAndMenuBarTests.swiftcmuxTests/TerminalUploadCommandTests.swift
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… receive Red on this commit. It blocks SIGTERM on the calling thread, which is the state a libdispatch worker spawns in, runs an upload command that traps SIGTERM and records that it arrived, and checks the record exists. Today it does not: a signal mask survives exec, so the command is handed ours and never sees the signal.
A signal mask survives exec, and cmux spawns upload commands and notification hooks from libdispatch workers, which run with most signals blocked. Without POSIX_SPAWN_SETSIGMASK the command inherits that mask, and so does everything it runs. A command that watches its own children through SIGCHLD then never learns they exited and waits out its internal timeouts instead. Measured with an uploader that reaps that way: each phase took exactly its own budget, 10003ms on a ten second probe and 45004ms on a forty-five second copy, for work that takes about a second. With the mask cleared the same phases took 103ms and 784ms. It only shows up under cmux because zsh clears the mask before it execs, while /bin/sh and bash pass it straight through, and /bin/sh -c is how both of these run. So the same command by hand is fast and nobody can reproduce the report. Only the mask is reset. Dispositions are left alone, so an inherited SIG_IGN on SIGPIPE still lets a child see EPIPE rather than dying mid-cleanup.
Red on this commit, and only reachable now that the previous one lets SIGTERM through. Each test starts a command whose shell exits on SIGTERM while a descendant it left behind ignores it, then checks the descendant is gone once the runner returns. It is not: both runners read the shell's exit as the command being over, skip the SIGKILL they owed the group, and leave the descendant running with the pipes open. While SIGTERM was blocked the shell always outlived the grace period, so the SIGKILL always went out and caught everything. That is why these tests pass on the commit before last and fail here.
Teardown sent SIGTERM to the group and escalated to SIGKILL only if the leader was still alive afterwards. A leader that dies on SIGTERM is not the group dying: a descendant that ignores SIGTERM survives, keeps the output pipes open, and stalls the drain to its own deadline. So the group is now signalled on its own account. SIGKILL goes out once the leader is gone or the grace period runs out, whichever comes first, and the leader is not reaped until that is done. The ordering matters: reaping the leader frees its pgid for reuse, and the kill would then be addressed to whatever group inherits the id. The upload runner splits its old reap into an observe step, waitid with WNOWAIT, and a collect step that runs after the escalation. The hook runner holds its exit handler back while the escalation timer still owes the group a signal, and that timer reaps and finishes the run itself.
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Merged, thank you @ejc3!! Upload commands and notification hooks now start with a clean signal mask, so uploads finish in about a second and cancelled ones stop leaving stray children. :D |
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Dropping a file onto a remote pane with a custom upload command configured took about a minute. The command itself, run by hand from a shell, finishes in about a second.
Repro: configure
terminal.uploadCommandswith any command that waits on child processes through SIGCHLD (an uploader written with tokio, for instance, or a Node script that spawnsscp), drop a file on an ssh pane, and time it. In my case every phase took exactly its own internal budget: 10003ms for a probe with a ten second timeout, 45003ms for a copy with a forty-five second one. The same drop with the mask cleared: 71ms and 570ms.The cause is the signal mask. cmux spawns upload commands and notification hooks with
posix_spawnfrom libdispatch workers, and dispatch worker threads run with most signals blocked. A signal mask survives exec, so withoutPOSIX_SPAWN_SETSIGMASKthe child starts with that mask and passes it on to everything it runs. A child that learns about its own children's exits through SIGCHLD never gets the signal, so each wait sits until its timeout fires. It never reproduces from a terminal because zsh clears the mask before it execs./bin/shand bash pass it straight through, and/bin/sh -cis how both spawn sites run the command.The fix sets an empty mask on the spawn attributes for both sites. Dispositions are left alone on purpose: cmux ignores SIGPIPE process-wide, children inherit that, and resetting it would make a child writing to a closed pipe die instead of seeing EPIPE.
Clearing the mask exposed a second bug that the blocked mask had been hiding. On timeout or cancel, both runners send SIGTERM to the process group and escalate to SIGKILL only if the group leader is still alive afterwards. While SIGTERM was blocked the leader always was, so the SIGKILL always went out and caught everything. Once SIGTERM is deliverable, a
/bin/shleader dies on it, the runner reads that as the command being finished, and a descendant that ignores SIGTERM survives with the output pipes still open, which then stalls the drain to its own deadline. The second half of the change signals the group on its own account: SIGKILL goes out once the leader is gone or the grace period runs out, and the leader is not reaped until that is done. Reaping first would free the pgid for reuse and the kill could land on an unrelated group. The upload runner splits its reap into an observe step (waitidwithWNOWAIT) and a collect step; the hook runner holds its exit handler back while the escalation timer still owes the group a signal.Commits go test, fix, test, fix so each red/green is visible. The teardown tests are deliberately after the mask fix: on the tree before it they pass, because the blocked mask is what kept the leader alive long enough to be killed.
Neither teardown test waits on a clock. Each one cancels the operation once the descendant has recorded its pid, and cancel runs the same SIGTERM → SIGKILL escalation the timeout does. The mask test has the command raise its own signal and run to completion, so teardown is not involved there at all.
Verified by running
TerminalCustomUploadRunnerTestsandTerminalNotificationPolicyEngineTestsat each of the four commits: the first reds only the mask test, the second is green, the third reds only the two teardown tests, and the fourth is green. The final tree ran green four times in a row.Need help on this PR? Tag
@codesmith-botwith what you need. Autofix is disabled.Summary by cubic
Fixes upload commands and notification hooks hanging for their full timeout by clearing the inherited signal mask at spawn, and fixes teardown so descendants that ignore SIGTERM no longer survive after the leader exits.
POSIX_SPAWN_SETSIGMASKat both spawn sites, leaving signal dispositions untouched.Written for commit dd1fd8c. Summary will update on new commits.
Summary by CodeRabbit