Hi,
Sorry for replying in a new thread.
Hi,
I have the strangest problem. I am running some complicated advanced
Bourne shell scripting. These scripts work fine under Ubuntu 14.04 LTS.
However, in Cygwin I have to add some strange commands with no obvious effect;
without these the scripts just hang. I can not disclose the scripts completely
because they are company property. I realise that this does not comply to the
rules of smart questions, but if anybody else has this problem the Cygwinners
need to know about it. I do not exactly know when these problems started. I
reinstalled Cygwin twice, several weeks ago and yesterday evening (25-2-2016).
I have had this problem with several complicated, lengthy scripts.
Debugging using echo debug statements is hard because the echo makes the
problem go away. When I discovered similar problems in multiple scripts, I
reinstalled Cygwin, but the problem persists. Also rebooting my Windows 7
Enterprise edition machine does not solve the problem. I have had some
experienced colleagues to look at this and they were as flabbergasted as I was.
Examples:
TTP_FILE_DR_KML=`echo $TTP_FILE.dr.kml | sed -s 's#\.txt\.#\.#g'`
#echo -n> /dev/null
sleep 0
if [ "`convert_needed "$TTP_FILE_DR_KML"`" = "convert" ]
then
In the examples above and below, either the sleep or the echo has to be
commented in, otherwise the script just hangs. In the example below the doit
function needs the echo or sleep, otherwise it does not return.
doit()
{
# 8< code removed
#echo -n
sleep 0
}
In
order to investigate this problem the Cywinners will need more
information. Feel free to ask, but it may not be legal for me to share.
Questions:
* Was a similar issue ever reported? I have looked, but did not find
anything.
* Is there a solution?
Thank you, kind regards, Matthijs.
Marco Atzeri answered:
I suspect you hit a corner case of resource race.
May be as the time for execution is very short :
$ time echo -n> /dev/null 0
real 0m0.000s
user 0m0.000s
sys 0m0.000s
$ time sleep 0
real 0m0.070s
user 0m0.015s
sys 0m0.062s
As both the two commands are just supposed to waste minimal time,
what was the original need of both of them ?
The explaination of the issue may not be clear. I have to add the sleep 0 or
the echo in order to keep my scripts running. Without these the scripts hang.
Sometimes they can be interrupted by CTRL-C, sometimes they do not respond. The
doit() function fails to end all together without the sleep. So the sleep 0 was
not there before, it is needed for the flow of the script all of a sudden.
Obviously, if adding an echo to a script changes the behaviour, it is kind of
hard to prove that an empty echo has an effect. Again, I showed it to two
colleagues who were surprised too. Together there was over 30 years of Bourne
shell experience looking at the problem.
The script containing the doit function is single-threaded, so there is no race
condition in the script. Actually, it should just end itself after the curly
brace. Without either the sleep or the echo it just hangs. Note also that the
reproducibility is 100%, which is not expected from a race condition of
marginal time differences. With reproducibility here I mean: adding the
sleep/echo gives the normal flow, removing the sleep/echo gives a hanging
script.
Questions:
* Were there changes in the Bourne shell interpreter in 2015/2016?
* Are these interpreters well-tested for regression?
* Are similar issues reported?
Thank you, kind regards, Matthijs.
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