You might also try running zope under runzope instead of under
zopectl. IIRC zopectl itself sets signal handlers and performs a
fork before starting zope, so the inherited environment may not be
what you think it is.
- C
On Oct 16, 2006, at 4:31 PM, Daniel Lopez wrote:
I made one tweak to the double-fork procedure, adding a waitpid
call in the grandparent process (the original zope thread) before
it returns out of the external method... the code then looked
something like:
[...prefork code up to here...]
pid1 = os.fork()
if pid1 > 0:
#grandparent waits for its child before returning
os.waitpid(pid1, 0)
return RESPONSE.redirect("wait_page")
pid2 = os.fork()
os.setsid()
if pid2 > 0:
#child quits, orphaning grandchild
sys.exit(0)
[...grandchild-only code after here...]
The waitpid call seems to be preventing the zombies... this is
good! (though if you find something bad about this approach, please
do speak up)
But in the process, a new bug was created, having to do with the
MySQL connection. I now receive a "Lost connection to MySQL server
during query" error in what appears to be a final db flush from the
grandparent's publish function (ZPublisher.Publish, line 104). The
good news is that the grandchild continues to do it's work, but the
bad news is that the user receives an error page instead of the
redirect to the "wait_page".
My guess is that this has something to do with the various forked
processes sharing the MySQL connection, and in particular, I'm
guessing the child process that exit(0)'s is closing the
connection, which is then unavailable when the grandparent tries to
use it.
Here's the interesting part: if I put a sleep(1) line in between
the waitpid() line and the return line, I get no error. It would
appear that the 1 second pause provides enough time for a new MySQL
connection to be made after the previous one is killed (less than 1
second is not enough).
This is a very ugly fix, though... I can't guarantee that 1 second
will always be enough... can anyone suggest a cleaner solution?
Perhaps I shouldn't kill the child with sys.exit(0)?
-Daniel
On Fri, 13 Oct 2006, Jonathan wrote:
Pls keep your posts on the list - so that others can help and so
that others can search for problems/solutions!
----- Original Message -----
Sent: Friday, October 13, 2006 12:13 PM
Subject: zope fork in external method
Jonathan-
I'm emailing you because I saw your post a few months back at:
http://mail.zope.org/pipermail/zope/2006-May/166574.html
I've been doing my best to find answers on existing posts, but to
no avail. Perhaps you can send further pointers?
On my system, a user can hit a page that initiates a long
database query. If the user hits the stop button and tries to
refresh, it messes things up (by interrupting the code upon
return of the query), so I came up with a solution that almost
works:
I put all the code into an external method, which forks. The
parent returns a redirect to a "waiting" throbber page that uses
Ajax to poll whether the query is done. The child then goes on
to do the hard work.
This is working as desired, with a single exception: zombie child
processes. Where can I learn more about forking processes in zope
external methods? I've read about the double-fork method, but
that hasn't resolved the problem...
A few ideas for reaping dead child processes:
1) implement a SIGCHLD handler
2) when a spawned child process is finished its 'zope processing'
have it write its process id to a file (be careful when accessing
files, you will need locking to eliminate problems that may be
caused by zope's multiple threads) and then have a clean up
routine which kills all of the processes listed in the file (this
could be an independant clean-up routine which wakes up on a
regular basis, or it could be built into the 'spawning' process
which does the clean up before it spawns a child).
3) as the last thing it does, have the child process issue a kill
-9 system command to kill its own process (I haven't tried this
myself, but it may work and it would be simple to implement)
Good luck!
Jonathan
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