[bugs #7340] xargs -n does not execute commands in a timely manner

[James Youngman]

This mail is an automated notification from the bugs tracker
 of the project: findutils.

/**************************************************************************/
[bugs #7340] Latest Modifications:

Changes by: 
                James Youngman <address@hidden>
'Date: 
                Wed 11/24/04 at 17:01 (GMT)

            What     | Removed                   | Added
---------------------------------------------------------------------------
          Resolution | Unreproducible            | Fixed


------------------ Additional Follow-up Comments ----------------------------
This problem is fixed in the CVS code for findutils.
To resolve your problem, you could either wait for the 
next official release of findutils, or check out a copy 
of the code from the CVS repository for findutils.







/**************************************************************************/
[bugs #7340] Full Item Snapshot:

URL: <http://savannah.gnu.org/bugs/?func=detailitem&item_id=7340>
Project: findutils
Submitted by: Stewart Brodie
On: Tue 01/20/04 at 14:15

Category:  xargs
Severity:  5 - Average
Item Group:  None
Resolution:  Fixed
Privacy:  Public
Assigned to:  None
Originator Name:  
Originator Email:  
Status:  Open
Release:  None
Fixed Release:  None


Summary:  xargs -n does not execute commands in a timely manner

Original Submission:  When the number of parameters to the xargs subcommand is 
limited by using -n <num>, xargs does not execute the subcommand until it has 
seen the end of the input stream OR num+1 arguments.  This can result in 
unnecessary delays in execution where the command to be executed is known (it 
has seen num args) since it isn't actually executed until more arguments are 
discovered (or the input stream ends).

A (lame, but the best I could think of right now) example which assumes date 
outputs 6 words:

$ for i in 1 2 3 4; do date;date;sleep 3; done | xargs -n 6

Example output from this is shown below, with me inserting <delay 3 seconds> 
where the 3 second delays occur:

Tue Jan 20 14:09:35 GMT 2004
<delay 3 seconds>
Tue Jan 20 14:09:35 GMT 2004
Tue Jan 20 14:09:38 GMT 2004
<delay 3 seconds>
Tue Jan 20 14:09:38 GMT 2004
Tue Jan 20 14:09:41 GMT 2004
<delay 3 seconds>
Tue Jan 20 14:09:41 GMT 2004
Tue Jan 20 14:09:44 GMT 2004
<delay 3 seconds>
Tue Jan 20 14:09:44 GMT 2004

There is no apparent reason why the delays are occurring where they are - the 
second echo should be being executed as soon as 6 parameters are available, no? 
 I don't think that the current behaviour is desirable (and it's a nuisance for 
my use of it).

I've tested this against findutils 4.1.7, but I've examined the latest 
(revision 1.17 of xargs/xargs.c) in CVS and it hasn't changed in this regard.

I think it would be fairly easy to fix this behaviour by inserting a check for 
reaching max_args near the end of the push_arg function after the new 
(non-NULL) argument has been added to the argument array, and calling do_exec 
immediately if the limit has been reached.

But I'm not certain, hence I'm not supplying a proposed patch at the moment.  
Does anybody else agree?



Follow-up Comments
------------------


-------------------------------------------------------
Date: Wed 11/24/04 at 17:01         By: James Youngman <jay>
This problem is fixed in the CVS code for findutils.
To resolve your problem, you could either wait for the 
next official release of findutils, or check out a copy 
of the code from the CVS repository for findutils.


-------------------------------------------------------
Date: Mon 11/01/04 at 10:47         By: Stewart Brodie <sbrodie>
I disagree.  I have improved testit.sh to more clearly demonstrate the problem. 
 It now has two echo commands with a sleep between them.  The first echo 
provides enough parameters for xargs to run immediately before the sleep 
occurs.  It doesn't actually execute until the echo after the sleep has 
executed.

I have tested and reproduced this behaviour against both versions 4.1.7 and 
4.2.3.

-------------------------------------------------------
Date: Sat 10/16/04 at 20:20         By: James Youngman <jay>
I have just retested this problem in findutils 4.2.0 with the "testit.sh" 
script (attached).  It looks right to me, could you comment on whether you 
agree?






File Attachments
-------------------

-------------------------------------------------------
Date: Mon 11/01/04 at 10:47  Name: test_sb.sh  Size: 86B   By: sbrodie
Simple shell script demonstrating the delay
http://savannah.gnu.org/bugs/download.php?item_id=7340&amp;item_file_id=1825

-------------------------------------------------------
Date: Sat 10/16/04 at 20:20  Name: testit.sh  Size: 179B   By: jay

http://savannah.gnu.org/bugs/download.php?item_id=7340&amp;item_file_id=1767






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