> [email protected] wrote:
>
> I have encountered a sporadic bug which I believe is in ksh (not in my
> ksh scripts). I'm trying to track this bug down so I can make a
> proper bug report. I believe it's caused by using a construct like in
> a "filter" script:
>
> /bin/cat FILE | while read a b c ;do
> blah && break
> echo $a $b $c
> done
>
> What I see in the process list is that the cat is hung. What I
> believe is happening is that some parent process which is reading the
> stdout of this process is somehow blocking, which is causing this
> process to block, which causes /bin/cat to block. I can see in the
> lsof output that there is a single reader of the stdout of /bin/cat.
Does the hang still occur if you change the example to:
-- snip --
while read a b c ;do
blah && break
echo $a $b $c
done < FILE
-- snip --
> This is all complicated by several layers of dotted (sourced) scripts,
> which don't show up in the process list. This bug does not occur in
> ksh88 running on AIX or Solaris, only in ksh93 running on Linux. It
> doesn't always occur in the same place (the bottom level script is the
> same, but the caller can be different from occurance to occurance).
> Additionally, it occurs only sometimes when it is run, making me think
> it involves some kind or resource issue or race condition.
>
> I have not yet had the chance of viewing this live while it's hung (it
> hangs in the middle of the night and it gets killed before I'm able to
> see what's going on).
Does Linux have some kind of equivalent for Solaris's /usr/bin/gcore to
get a core sample of the hanging process ?
[snip]
> Any thoughts on how I can tell what's actually happening to cause this
> hang? Or what would be useful for a bug report? Any particular tools
> which are useful other than ps/lsof/strace/vim?
1. Can you please try to obtain stacktraces of the "cat" and the shell
process for both your script version and the "cat"-less version above,
please (at least on Solaris you could try to obtain stack traces via $
/usr/bin/pstack <pid> # or the "dbx"/"gdb" debuggers) ?
2. Which ksh93 version do you use, e.g what does $ print
"${.sh.version}" # say ?
3. In which locale does the script run, e.g. what does $ env | egrep
'^(LANG|LC_)' # say ?
----
Bye,
Roland
--
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