fix(tasks): preserve output from short shell commands - #4159
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Register stdout and stderr readers before launching their goroutines so WaitLog cannot observe an empty WaitGroup. Apply this to both server-local tasks and remote runner jobs. Drain both pipes before calling cmd.Wait. Go documents that Wait releases Cmd resources, while StdoutPipe and StderrPipe require all reads to finish before Wait is called. Otherwise, output from short-lived processes may be lost when Wait closes the pipes. References: - https://pkg.go.dev/os/exec#Cmd.Wait - https://pkg.go.dev/os/exec#Cmd.StdoutPipe - https://pkg.go.dev/os/exec#Cmd.StderrPipe
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ChangesShell output synchronization
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: ⚪ Minimal · up to The PR fixes lost shell-task output and adds regression coverage; no actionable merge-blocking risk remains, so it is merge-ready after normal checks. Sequence Diagram(s)sequenceDiagram
participant ShellAppRun
participant Logger
participant Command
ShellAppRun->>Logger: Start stdout and stderr readers
ShellAppRun->>Logger: WaitLog()
Logger-->>ShellAppRun: Output readers complete
ShellAppRun->>Command: Wait()
Command-->>ShellAppRun: Process wait result
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Actionable comments posted: 1
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Inline comments:
In `@db_lib/ShellApp_test.go`:
- Around line 16-31: Extend stdoutCaptureLogger and its LogCmd/WaitLog methods
to register and drain cmd.StderrPipe alongside stdout, reading both streams
concurrently and retaining any read errors. Update the regression test
assertions to verify captured stderr output as well as stdout.
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db_lib/ShellApp.godb_lib/ShellApp_test.goservices/runners/running_job.goservices/tasks/TaskRunner_logging.go
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Pull request overview
Fixes lost stdout/stderr from short-lived shell tasks by coordinating command completion with log readers.
Changes:
- Registers log readers before goroutine startup.
- Drains command output before
Wait. - Adds shell-output regression coverage.
Reviewed changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
services/tasks/TaskRunner_logging.go |
Fixes task logger wait-group registration. |
services/runners/running_job.go |
Fixes runner logger wait-group registration. |
db_lib/ShellApp.go |
Reorders output draining and process waiting. |
db_lib/ShellApp_test.go |
Tests stdout/stderr preservation. |
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| // Wait for all log processing to complete before returning | ||
| // Drain stdout/stderr before calling Wait, because it releases any resources | ||
| // associated with the Cmd. | ||
| t.Logger.WaitLog() |
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@rzaitov it looks like we should use cmd.Poccess.Wait() which doesn't close descriptors. After that do t.Logger.WaitLog() with deadline and only after that call cmd.Wait()
| } | ||
| t.Cleanup(func() { util.Config = previousConfig }) | ||
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| logger := &outputCaptureLogger{} |
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Pull request overview
Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.
Suppressed comments (1)
db_lib/ShellApp_test.go:43
- This regression is timing-dependent: both reader goroutines start immediately, so the test can still capture these tiny writes with the old
cmd.Wait(); WaitLog()implementation and pass. Make the test deterministic by blocking both readers on a channel thatWaitLogreleases; then the old ordering closes the pipes before reads begin, while the new ordering drains them first.
go func() {
defer l.wg.Done()
l.stdout, l.stdoutErr = io.ReadAll(stdout)
}()
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I think this is more suitable solution: #4161 |
Summary
Fix stdout/stderr being lost when short-lived shell tasks finish before their log-reader goroutines drain the command pipes.
cmd.Wait().WaitGroupbefore starting their goroutines.Go documents that
Cmd.Waitcloses pipes returned byStdoutPipeandStderrPipe, so reads must complete beforeWaitreturns:Fixes #3078
Also addresses #3700, which reports the same successful Bash task with no script output.
Testing
go test -race ./db_lib ./services/tasks ./services/runners -count=1Summary by CodeRabbit
Bug Fixes
Tests