On 11/26/18 8:29 AM, Phil Steitz wrote:
On 11/26/18 6:19 AM, Mark Struberg wrote:
Hi Phil!
Let me start by repeating that other than trying to help diagnose
bugs and answer user questions, I don't really work on [pool] any
more, so I don't really have any standing here. You are the RM,
so it is completely up to you and the active Commons committers to
decide what to do with the code. So fine to ignore my comments.
I think that the right answer here is WONT_FIX. That sounds
harsh, but it seems to me
that the obvious solution here is for the user to set maxIdle to
at least 1.
I thought about that as well!
Setting maxIdle to 1 will make it less likely but a deadlock will
STILL happen.
I am not sure this is right. If maxIdle >0, the fix for POOL-240
(a similar liveness issue) should kick in and work. Each time a
validation or passivation failure occurs on return, there is a
call to ensureIdle that will create a new instance and add it to
the pool if there is capacity to do so.
So I fear we really need to tackle this. Stackoverflow and our
own bug tracker is full of such reports :(
I see one additional actual report on GKOP (the other linked
issue, which should be similarly patched if the consensus is to do
this for GOP). The vast majority of the liveness reports that we
have gotten over the years in DBCP and pool are just pool
exhausted due to failure to return instances.
The workaround violating maxIdle will restore liveness, but is
likely the wrong solution here. Again, up to you guys to judge.
Note that when you specify maxIdle equal to 1 you are telling the
pool to destroy all returning instances. To use the pool in this
way is silly, IMO. With your patch, new instances are still
created for *every* borrow. The pool and all of its machinery is
doing nothing other than tracking the number of active instances
and making sure life cycle events are fired. If you want the
semantics of returning object with threads waiting to be that the
returning object is passivated, activated and handed directly to a
waiter without every hitting the idle instance pool, that would
require rewriting a fair bit of the borrow / return code. It is
an interesting idea and would solve the POOL-240 as well.
One final comment. If you stick with something like what is in
the code now, you should make sure to passivate the new instance
before putting it into the pool. I just noticed that ensureIdle
does not do that, which I think is a bug in that method. So if
you want to proceed with this fix, I would recommend
1. Move the ensureIdle activations added in POOL-240 into destroy
itself.
2. Add passivation to ensureIdle
Sorry, looks to me like this is not actually necessary. So I take
back my comment that this is a bug in ensureIdle.
3. Implement corresponding workaround for GKOP
Phil
LieGrue,
strub
Am 23.11.2018 um 16:51 schrieb Phil Steitz<phil.ste...@gmail.com>:
On 11/23/18 2:57 AM, Mark Struberg wrote:
should read: This change (putting a new item back to the idle
pool) was needed to prevent a dead-lock....
*grabbing a fresh coffee* le
I am sorry I did not look carefully enough at this issue before
reviewing the change. After reviewing the DBCP ticket (OP
likely unrelated, IMO), I think that the right answer here is
WONT_FIX. That sounds harsh, but it seems to me that the obvious
solution here is for the user to set maxIdle to at least 1.
What the fix does is effectively that, without changing the
setting. If waiting threads die or time out while the create is
happening, there will be an idle instance in the pool and for
certain one is being put there on the way to getting checked
back out. See comments on POOL-327.
If the consensus is to insert this workaround to enable the pool
to retain liveness in the use case, it's probably best to use
ensureIdle(1, false) (see POOL-240). It could be that just
moving the call to ensureIdle inside destroy would be OK. But
as stated above, this breaks the maxIdle contract.
I see that your original report / use case here is from DBCP,
Mark. Was it prepared statements or connections that you were
trying to limit to 0 idle? Is there a reason that just using 1
would not work?
Phil
Am 23.11.2018 um 10:49 schrieb Mark Struberg<strub...@yahoo.de>:
This change (putting a new item back to the idle pool was
needed to prevent a dead-pool
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