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yet another locking ?
Author: Jim Davis
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:21260#107669
----- Excess quoted text cut - see Original Post for more -----
Sort of... But in 5.0 the whole shebang was considered a single unit
(sort of). So if the system automatically locks (as it does in MX) does
it lock all members of a nested structure set when any of the members
are accessed?
In other words whether we call it a race condition or not, do we have to
lock it?
Jim Davis
Author: Stephen Moretti
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:21260#107668
Jim,
----- Excess quoted text cut - see Original Post for more -----
I'm not certain, but this looks like a race condition to me.
Just a thought...
Regards
Stephen
Author: Mike Brunt
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:21260#107565
But is still very relevant up to CFMX even though it was written relating to
version 4.51 and written very well IMHO, thanks Jim.
Here is an article from Macromedia regarding locking on ColdFusion MX.
http://www.macromedia.com/v1/Handlers/index.cfm?ID=23021&Method=full
Kind Regards - Mike Brunt
Webapper Services LLC
Web Site http://www.webapper.com
Blog http://www.webapper.net
Webapper <Web Application Specialists>
> so i take it the answer is no:)
>
> i did go read this tut
> http://www.vboston.com/depressedpress/content/coldfusion/guide
> s/locking/5-us
> ingcflock.cfm
> bear in mind it looks to be written for 4.5
It definitely was (I wrote it) - I'm doing the research needed to update
it to MX now, but am getting a lot of "shoulds" and "most likelys"
instead of "will" and "always" when I ask questions. ;^)
Jim Davis
Author: Jim Davis
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:21260#107547
> so i take it the answer is no:)
>
> i did go read this tut
> http://www.vboston.com/depressedpress/content/coldfusion/guide
> s/locking/5-us
> ingcflock.cfm
> bear in mind it looks to be written for 4.5
It definitely was (I wrote it) - I'm doing the research needed to update
it to MX now, but am getting a lot of "shoulds" and "most likelys"
instead of "will" and "always" when I ask questions. ;^)
Jim Davis
Author: Jim Davis
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:21260#107541
----- Excess quoted text cut - see Original Post for more -----
There's been a lot of talking about this and here's what I've gleaned
(but not confirmed). I'd like to confirm these however so I can update
my Guide to Locking.
1) At the very least if you want to maintain possible compatibility with
CF 5 or below you should agressively lock. In most applications this
isn't an issue, but it is for people that want to sell/distribute
applications or tags that may be used in the older environments.
2) In CF 5 and earlier failure to lock would, under load, cause server
corruption. You'd crash the box, period. In CFMX the scopes are
thread-safe so you don't need to worry about taking down the server even
if you never lock at all.
3) However, and here's the tricky part, although CFMX won't crash due to
poor locking there's also no gaurantee that it'll return proper values.
The internal locking (implemented in Hash Tables) is, as I understand
it, much more "atomic" than CF 5.0.
If, for example, you have two nested structures I think that one could
be locked while the other isn't. This means that you might read the
"good" version of the child while the parent is being written (and,
presumably before the child is written too).
4) Also the locking behavior for pointer-linked structs seems a little
confused. For example in CF 5 and below if you created a pointer to the
session scope in the application scope you'd have to lock both scopes
when accessing them. (Although note that this is INCREDIBLY useful to
see how many people are logged in and get access to their data!)
I _think_ that you can safely ignore locking them in MX, but I've not
gotten a definitive answer.
5) Reads definitely do not have to be locked in MX as they were in 5.
For example in 5 you needed to lock the IsDefined() function - you
simply don't in MX. However unlocked reads may not return the data
you'd expect in all situations.
6) Race conditions and transactional processing should still be locked
ONLY to protect your data NOT (as was the case in 5) to protect the
stability of the server.
In the end the bottom-line seems to be that MX won't crash if you ignore
locking, but it may not work the way you'd expect.
Also remember that there are actually many ways in which race conditions
can occur. The obvious ones are Frames and multiple windows (whether
programmed or user-launched). However the Application and Server scopes
are multi-thread accessed as a matter of course.
Even with the session scope there are other ways. Each resource on a
page is called by a separate thread (for example if you have CF
generated style sheets or Javascript files then they might run
concurrantly with the main template). Using FlashComm on a page can
create multi-threaded accesses to the session as can something as simple
as a user pressing a submit button multiple times.
In my experience users opening multiple windows has been the biggest
problem, but the submit button thing is another biggie.
Anyways... Anybody have definitive answers/comments on the above points?
Jim Davis
Author: Dave Lyons
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:21260#107506
yes, thanks
i appreciate the effort though:)
looks like quite a few people are confused on it.
i can see tony now...unlocking...unlocking...unlocking
lol
Dave
----- Excess quoted text cut - see Original Post for more -----
http://www.vboston.com/depressedpress/content/coldfusion/guides/locking/5-us
----- Excess quoted text cut - see Original Post for more -----
scopes:
> > > the reason you do not need to lock them (unless you are attempting
to
> > > prevent a race condition) is that their underlying Java
implementations
----- Excess quoted text cut - see Original Post for more -----
a
> > > > default value will not cause a race condition, because the
value
will
----- Excess quoted text cut - see Original Post for more -----
Author: Stephen Moretti
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:21260#107497
Dave,
That article is relevant to CF4.x and CF5, but not CFMX
Regards
Stephen
> so i take it the answer is no:)
>
> i did go read this tut
>
http://www.vboston.com/depressedpress/content/coldfusion/guides/locking/5-us
----- Excess quoted text cut - see Original Post for more -----
Author: Dave Lyons
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:21260#107485
so i take it the answer is no:)
i did go read this tut
http://www.vboston.com/depressedpress/content/coldfusion/guides/locking/5-us
ingcflock.cfm
bear in mind it looks to be written for 4.5
Dave
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----- Excess quoted text cut - see Original Post for more -----
Author: Christian Cantrell
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:21260#107473
Just some additional interesting information on shared variable scopes:
the reason you do not need to lock them (unless you are attempting to
prevent a race condition) is that their underlying Java implementations
use java.util.Hashtables. Hashtables are synchronized so that two
threads cannot modify the same instance of a Hashtable concurrently.
So Tony, you are right that Macromedia engineers did the right thing
here, otherwise there would be a lot more cflocking going on. For
instance, if they had used a HashMap, all access/modification would
have to be locked (to prevent actual exceptions as opposed to just
unexpected behavior), which would make for a lot more code with no
advantages.
Another thing to note is that synchronization at such a low level is
very fast and efficient; faster than using cflocks.
Christian
On Thursday, February 6, 2003, at 10:19 AM, Tony Weeg wrote:
----- Excess quoted text cut - see Original Post for more -----
Author: Tony Weeg
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:21260#107440
cool.
that makes sense...and from what I understand, it makes
perfect sense, that macromedia planned around that, and
did some homework for us.
thanks!
...tony
Tony Weeg
Senior Web Developer
UnCertified Advanced ColdFusion Developer
Information System Design
Navtrak, Inc.
Mobile workforce monitoring, mapping & reporting
www.navtrak.net
410.548.2337
----- Excess quoted text cut - see Original Post for more -----
Yes, but then every use of a shared scope variable isn't necessarily
going
to generate a race condition.
Simply checking for an application scope variable and setting it to a
default value will not cause a race condition, because the value will
always
be the same. Only if you're reading and then incrementing that
application
scope variable will you get a race condition.
In your example of a shopping cart, locking was required in CF5 and
lower
because of other issues with session variables. Using session variables
in
a CFMX application you are unlikely to get a race condition, unless
you're
using frames in the design of your site.
You don't get a race condition if you're only reading a variable and not
updating, so you don't need a lock.
Stephen
Author: Stephen Moretti
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:21260#107438
----- Excess quoted text cut - see Original Post for more -----
Yes, but then every use of a shared scope variable isn't necessarily going
to generate a race condition.
Simply checking for an application scope variable and setting it to a
default value will not cause a race condition, because the value will always
be the same. Only if you're reading and then incrementing that application
scope variable will you get a race condition.
In your example of a shopping cart, locking was required in CF5 and lower
because of other issues with session variables. Using session variables in
a CFMX application you are unlikely to get a race condition, unless you're
using frames in the design of your site.
You don't get a race condition if you're only reading a variable and not
updating, so you don't need a lock.
Stephen
Author: Tony Weeg
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:21260#107430
http://www.duke.edu/web/cps001/labs/lab11/lab11.html
is an applet, to actually watch it happen.
...tony
Tony Weeg
Senior Web Developer
UnCertified Advanced ColdFusion Developer
Information System Design
Navtrak, Inc.
Mobile workforce monitoring, mapping & reporting
www.navtrak.net
410.548.2337
> but when isnt there a chance of a race condition occuring.
> to me, on any HA site, you might have the opportunity for
> a race condition occuring. things with computers, as I have
> learned over the years, are cut and dry 1's and 0', why can no
> one give us a definitive answer on locking shared scope variables?
>
This is the definitive answer. Its the same answer you'll get from Ray
Camden, Simon Horwith, Christian Cantrell etc.
Tony, I suspect that you may not understand exactly what a "race
condition"
is in terms of locking records and/or shared scope variables and would
recommend looking up record locking in more detail. I tried to find a
decent article on this, but this :
http://www.linuxfocus.org/English/September2001/article198.meta.shtml
is
the
best I could find...
Regards
Stephen
Author: Tony Weeg
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:21260#107427
well, your supposition is wrong :) sorry.
I definitely understand a race condition. what I don't
understand is this: If a race condition could occur, even
1 time out of 1 hundred thousand iterations, isnt that enough
to lock it? I could imagine, if I had a shopping cart system,
that I would EVER want someone to know what my CC info
was, however, if a race condition is even somewhat a potentiality
then even the smallest chance of occurrence is too much of a risk
wouldn't you agree?
btw, here is what I found about six months ago, and read to help
understand
this concept, its pretty helpful...there is also a java based
graphic/animation simulation
that explains this, and you can actually watch it happen...not sure of
the url
but here is the one I read..
http://www.cs.mtu.edu/~shene/NSF-3/e-Book/MUTEX/TM-example-philos-1.html
...tony
Tony Weeg
Senior Web Developer
UnCertified Advanced ColdFusion Developer
Information System Design
Navtrak, Inc.
Mobile workforce monitoring, mapping & reporting
www.navtrak.net
410.548.2337
> but when isnt there a chance of a race condition occuring.
> to me, on any HA site, you might have the opportunity for
> a race condition occuring. things with computers, as I have
> learned over the years, are cut and dry 1's and 0', why can no
> one give us a definitive answer on locking shared scope variables?
>
This is the definitive answer. Its the same answer you'll get from Ray
Camden, Simon Horwith, Christian Cantrell etc.
Tony, I suspect that you may not understand exactly what a "race
condition"
is in terms of locking records and/or shared scope variables and would
recommend looking up record locking in more detail. I tried to find a
decent article on this, but this :
http://www.linuxfocus.org/English/September2001/article198.meta.shtml
is
the
best I could find...
Regards
Stephen
Author: Stephen Moretti
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:21260#107422
> but when isnt there a chance of a race condition occuring.
> to me, on any HA site, you might have the opportunity for
> a race condition occuring. things with computers, as I have
> learned over the years, are cut and dry 1's and 0', why can no
> one give us a definitive answer on locking shared scope variables?
>
This is the definitive answer. Its the same answer you'll get from Ray
Camden, Simon Horwith, Christian Cantrell etc.
Tony, I suspect that you may not understand exactly what a "race condition"
is in terms of locking records and/or shared scope variables and would
recommend looking up record locking in more detail. I tried to find a
decent article on this, but this :
http://www.linuxfocus.org/English/September2001/article198.meta.shtml
is the
best I could find...
Regards
Stephen
Author: Tony Weeg
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:21260#107397
but when isnt there a chance of a race condition occuring.
to me, on any HA site, you might have the opportunity for
a race condition occuring. things with computers, as I have
learned over the years, are cut and dry 1's and 0', why can no
one give us a definitive answer on locking shared scope variables?
off I go into the wild locking yonder.....locking locking locking away
:)
...tony
Tony Weeg
Senior Web Developer
UnCertified Advanced ColdFusion Developer
Information System Design
Navtrak, Inc.
Mobile workforce monitoring, mapping & reporting
www.navtrak.net
410.548.2337
Dave,
With CFMX you do not need to use CFLOCK on shared scope variables
(session,
application, server) UNLESS there is a chance of a race condition
occurring.
See
http://users.evitech.fi/~tk/rtp/parallel-programming-theory.html#race_co
ndit
ion for a brief description of race conditions.
Regards
Stephen
> im a bit confused and after scouring through the archives and all my
emails and the MM boards, I am left a bit confused.
> I'm running cfmx
> and I have seen that some people say that with cfmx that you don't
need to
lock your sessions at all and some say you need to lock everything.
>
> most of my sites wont need to be locked I'm assuming, small ones,
mostly
with just 1 admin user at a time.
>
> But I have several huge sites coming up (one of the reasons I am
moving
over to cfm) and the will have several hundred to over a 1000 people on
at a
time.
>
> I'm more concerned with the bigger sites obviously.
> I cant really find my answer in either book I am reading either (bens
big
ass, heavier than sh*t, already crushed my frickin foot with goliath!
excellent book though!) and (the 10 steps book) btw~ both books need
more
pix! ha-ha
----- Excess quoted text cut - see Original Post for more -----
Author: Stephen Moretti
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:21260#107396
Dave,
With CFMX you do not need to use CFLOCK on shared scope variables (session,
application, server) UNLESS there is a chance of a race condition occurring.
See
http://users.evitech.fi/~tk/rtp/parallel-programming-theory.html#race_condit
ion for a brief description of race conditions.
Regards
Stephen
> im a bit confused and after scouring through the archives and all my
emails and the MM boards, I am left a bit confused.
> I'm running cfmx
> and I have seen that some people say that with cfmx that you don't need to
lock your sessions at all and some say you need to lock everything.
>
> most of my sites wont need to be locked I'm assuming, small ones, mostly
with just 1 admin user at a time.
>
> But I have several huge sites coming up (one of the reasons I am moving
over to cfm) and the will have several hundred to over a 1000 people on at a
time.
>
> I'm more concerned with the bigger sites obviously.
> I cant really find my answer in either book I am reading either (bens big
ass, heavier than sh*t, already crushed my frickin foot with goliath!
excellent book though!) and (the 10 steps book) btw~ both books need more
pix! ha-ha
----- Excess quoted text cut - see Original Post for more -----
Author: Dave Lyons
Short Link: http://www.houseoffusion.com/groups/cf-talk/thread.cfm/threadid:21260#107394
im a bit confused and after scouring through the archives and all my emails and
the MM boards, I am left a bit confused.
I'm running cfmx
and I have seen that some people say that with cfmx that you don't need to lock
your sessions at all and some say you need to lock everything.
most of my sites wont need to be locked I'm assuming, small ones, mostly with
just 1 admin user at a time.
But I have several huge sites coming up (one of the reasons I am moving over to
cfm) and the will have several hundred to over a 1000 people on at a time.
I'm more concerned with the bigger sites obviously.
I cant really find my answer in either book I am reading either (bens big ass,
heavier than sh*t, already crushed my frickin foot with goliath! excellent book
though!) and (the 10 steps book) btw~ both books need more pix! ha-ha
so I wanted your guys recommendations
Dave
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May 24, 2012
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