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Re: "echo | ps -j $(:) | cat | cat | cat" runs components in different process groups
- X-seq: zsh-workers 42516
- From: Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx>
- To: Zsh hackers list <zsh-workers@xxxxxxx>
- Subject: Re: "echo | ps -j $(:) | cat | cat | cat" runs components in different process groups
- Date: Fri, 23 Mar 2018 22:19:59 -0700
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On Mar 23, 4:36pm, Bart Schaefer wrote:
} Zsh wants to use "echo" as the group leader because it was the first to
} fork, but because $(:) delayed the execution of "ps" the "echo" process
} has already exited and cannot be made group leader. As the fallback the
} other processes each get made into its own process group.
} So it's a race condition, adding the process substitution just happens
} to expose it.
It may be this easy?
It fixes the specific example in the subject by causing the zsh parent
shell to re-assume job leader for all subsequent processes in the pipeline
if the current leader is dead. However, I'm concerned that if the first
leader is reaped after a few processes in a long pipeline are created,
there may still be a new process group asserted for remaining processes.
On the other hand I haven't found an example where that occurs, instead
I get jobs where the process group ID is the PID of the now-dead leader.
It could be I just haven't constructed the right test.
In any case "make check" still passes and this appears to be better than
the previous situation.
diff --git a/Src/exec.c b/Src/exec.c
index 35b0bb1..52b0eb4 100644
@@ -3455,6 +3455,7 @@ execcmd_exec(Estate state, Execcmd_params eparams,
if (type == WC_SUBSH && !(how & Z_ASYNC))
flags |= ESUB_JOB_CONTROL;
filelist = jobtab[thisjob].filelist;
+ list_pipe_child = list_pipe;
forked = 1;
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