os/exec: Cmd.ProcessState field not always populated after (*Cmd.Run) returns #56002
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ianlancetaylor
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Change https://go.dev/cl/437996 mentions this issue: |
romaindoumenc
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Nov 3, 2022
Wait or Run will populate its ProcessState when the command completes. Fixes golang#56002. Change-Id: I21547431f5d2d3e0fc0734fd1705421a0ac4209c Reviewed-on: https://go-review.googlesource.com/c/go/+/437996 Auto-Submit: Bryan Mills <bcmills@google.com> TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Rob Pike <r@golang.org> Run-TryBot: Ian Lance Taylor <iant@google.com> Auto-Submit: Ian Lance Taylor <iant@google.com> Reviewed-by: Bryan Mills <bcmills@google.com> Run-TryBot: Bryan Mills <bcmills@google.com> Reviewed-by: Ian Lance Taylor <iant@google.com>
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What version of Go are you using (
go version)?Does this issue reproduce with the latest release?
Yes.
What operating system and processor architecture are you using (
go env)?go envOutputWhat did you do?
Read the documentation for the
os/execpackage'sCmd.ProcessStatefield. Note that it promises that its value will be available "after a call toWaitorRun.Write a program that calls on the
(*Cmd).Runmethod that invokes a nominated command that does not exist (that is, theCmd.Pathfield's value does not designate a readable, executable file), then attempt to call methods on the*os.ProcessStatefield value that I expect to be present in theCmd's "ProcessState" field.What did you expect to see?
The
Cmd's "ProcessField" value would be a non-nil pointer to anos.ProcessState.What did you see instead?
My program panics dereferencing a nil pointer. The
Cmd.ProcessStatefield remains nil after(*Cmd).Runreturns.Diagnosis
(*Cmd).Runis a macro operation that does the following:(*Cmd).Start.(*Cmd).Wait.It turns out that only after
(*Cmd).Waitreturns—assuming that(*Cmd).Startwas called first, and that it hasn't been called already—is theCmd.ProcessStatefield populated. If(*Cmd).Run's invocation of(*Cmd).Startfails, then the field will not be populated.The documentation is simple, but misleading. It would be more accurate to say that the
Cmd.ProcessStatefield will be populated after(*Cmd).Runstarts the command.I came upon this discrepancy while debugging a program that panicked in this situation. It took a while to figure out that the path to the command I was nominating in the
Cmd.Pathfield was wrong, such that(*Cmd).Start—invoked via(*Cmd).Run—was failing. I figured that(*Cmd).Runhad returned, even if it had returned an error, so I could count on theCmd.ProcessStatefield's value being available for use.The text was updated successfully, but these errors were encountered: