Object allocations, memory and UINavigationController

I'm having a problem with object allocations
Is it possible to release/remove a view from a navigation controller stack when I click on the back button on my navigation controller? I wish to get rid of the view I just left (the one disappearing to the right of the screen). The problem is that the next time I navigate to the same view lots of new objects are allocated, and none of the old ones are released.
In the tableView:didSelectRowAtIndexPath: method I initialize a new view controller for the view I want to push to the stack and assign it to a property. The problem is that the old view seems to continue to exist in the navigation controller stack, because it's never released according to the "object allocation" section in Instruments, thus the amount of allocated objects and memory just grows and grows as I click back and forth in my navigation controller.
For example, if I click on a cell in the first table view (which displays a second view) and then click on the back button and then click on the first cell again, the second view and all of its objects are created again, but the previous instance of this view seems to still exist somewhere in the navigation controller stack.
What's the best way to solve this?
Here's some of the code in the "tableView:didSelectRowAtIndexPath:" method:
self.categoryController = [[CategoryViewController alloc] init];
self.categoryController.category = category;
[self.navigationController pushViewController: self.categoryController animated:YES];
Each time this code is executed tons of new objects are allocated, but the objects allocated by the previous CategoryViewController are not released.

Thanks you so much for the great article!!
cotton.m!!
I can cheat on my assignment again, haha!
strange
Stepwise Refinement :|
http://forum.java.sun.com//thread.jspa?threadID=5206258

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CHECKDB found 0 allocation errors and 1 consistency errors in table 'sys.syscolpars' (object ID 41)

Msg 2511, Level 16, State 2, Line 1
Table error: Object ID 41, index ID 1, partition ID 281474979397632, alloc unit ID 281474979397632 (type In-row data). Keys out of order on page (1:187), slots 9 and 10.
CHECKDB found 0 allocation errors and 1 consistency errors in table 'sys.syscolpars' (object ID 41).
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repair_rebuild is the minimum repair level for the errors found by DBCC CHECKDB (adv_tvs).
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Hi Rapunzel,
The minimum repair suggested is repair_rebuild you can try that. As per mssage there is corruption in your database and it can only be corrected by either repairing or Restoring from known good backup.For doing repair the database must be in single-user
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The truth about objects, references, instances and cloning (Trees and Lists

Hello
As a few of you may have know from my postings over the past few weeks, ive been building my first real java ap and trying to learn along the way, hitting a few snags here and there.
One main snag i seem to have been hitting a fair bit is objects and instances, im kinda learning on how they work and what they mean but as a php programmer it seems to be very different.
as pointed out to me if you have objectA=objectB then in php you have two objects that share the same value but in java you have still one object value and one object pointing to the value.
sooo my first question is
if i have this
Object objA=new Object()
Object objB=objA()then object A creates a new memory allocation for the object data right? and object B is simply a reference to the object A memory allocation right?
so therefore there is no instance of objectB? or is there an instance of object B but it just takes up the same memory allocation as object A?
anyway, what is the point of being able to say objB=objA what can that be used for if not for making a copy of an object (i understand now that it doesnt copy an object)
My second question (which i think i actually understand now, but im posting it to see if the answers may help others)
If i have a List structure (e.g. arraylist) then when i add a datatype such as a treemap does it not add the changed treemap, ill try and explain with code
ArrayList mylist=new ArrayList()
Treemap myTree=new Treemap()
myTree.put("hello","howdy");
myTree.put("bye","cya");
mylist.put(myTree);
System.out.println(mylist.toString());
myTree.put("another","one");
mylist.put(myTree);
System.out.println(mylist.toString());now to be honest ive not actually tried that code and it may actually procude the right results, but from my experience so far that similar sort of thing hasnt been working (by the way i know the above code wont compile as is :p)
anyway what i assume is that will output this
[Hello,howdy,bye,cya] <<this is the first system out
[Hello,howdy,bye,cya,another,one <<this is the second system out
Hello,howdy,bye,cya,another,one] <<this is the second system out
where it should produce this
[Hello,howdy,bye,cya,
Hello,howdy,bye,cya,another,one]
Why when I update the treemap does the arraylist change, is this because the thing that is being put in the array list is infact not an object but simply a reference to an object?
thanks for everyones help so far :)

as pointed out to me if you have objectA=objectB then
in php you have two objects that share the same value
but in java you have still one object value and one
object pointing to the value.Some years ago, I built a small website managing data saved in an XML file using PHP. Being used to Java, I used an OO approach and created classes managing data structures and having setter/getter methods. The fact that PHP did actually create a copy of any object being passed as and argument made me crazy. This way, I wasn't able to reach the same instances from several different places in my code. Instead, I had to put a certain operator ("&" I think) before any reference to force PHP not to make a copy but pass the reference. I also found a note on the PHP site saying that copying was faster than passing the reference, which I actually couldn't believe. If I'm not wrong, they changed the default behaviour in PHP5.
if i have this
Object objA=new Object()
Object objB=objA()then object A creates a new memory allocation for the
object data right? and object B is simply a reference
to the object A memory allocation right?The statement "new <Class>" allocates memory. The reference itself just takes up a few bytes in order to maintain some administrative data (such as the memory address). References are basically like pointers in C, though there's no pointer arithmetics and they can't point to any arbitrary place in memory (only a legal instance or null).
so therefore there is no instance of objectB? or is
there an instance of object B but it just takes up
the same memory allocation as object A?There is an instance of objectB, but it's just the same instance that objectA is pointing at. Both references objectA and objectB contain the same memory address. That's why they'd produce a result of "true" if compared using the "==" operator.
anyway, what is the point of being able to say
objB=objA what can that be used for if not for making
a copy of an object (i understand now that it doesnt
copy an object)Sometimes you don't want to make a copy, as 1) it consumes more memory and 2) you'd lose the reference to it (making it more difficult to tell what instance is actually accessed). If there was no way to pass a reference to an object into a method, methods wouldn't be able to affect the original instance.
Why when I update the treemap does the arraylist
change, is this because the thing that is being put
in the array list is infact not an object but simply
a reference to an object?The ArrayList doesn't change at all. It's the instance that's being changed, and the ArrayList has a reference to it.

Why are object alloc delays occuring outside of GC?

Hi
I'm currently tuning an application which has a low latency transaction requirement (sub 5ms ideally), hence we're using JRockit RT with an 8ms deterministic strategy (we're not achieving 8ms GC pause, but some time ago we experimented and found this was a good setting for us).
I'm currently focused on addressing latency spikes which we're hoping to bring down from many hundreds of ms to the order of 10-20ms. Many of the spikes are occurring during GC activity as one would expect, but I'm currently looking at some spikes outside of GC which I'm struggling to understand the cause of. What I seem to be seeing is object alloc delays which are occuring and then being resolved, but outside of any GC activity.
For example, see the following snippet from the log. Cmd line params include:
-Xverbose:memory,memdbg=debug,gcpause=debug,compaction,gcreport,refobj
-Xgcprio:deterministic
-Xpausetarget=8ms
Version=
java version "1.6.0_05"
Java(TM) SE Runtime Environment (build 1.6.0_05-b13)
BEA JRockit(R) (build R27.6.0-50_o-100423-1.6.0_05-20080626-2104-linux-x86_64, compiled mode)
[memory ][Wed May 26 12:31:38 2010][23134] Pause 'OC:Cleanup' took 0.179 ms (ended at 1545.738649 s).
[memory ][Wed May 26 12:31:38 2010][23134] 1539.900-1545.738: GC 13279297K->11726889K (14680064K), sum of pauses 386.637 ms
[memdbg ][Wed May 26 12:31:38 2010][23134] Page faults before GC: 1, page faults after GC: 1, pages in heap: 3670016
[finaliz][Wed May 26 12:31:38 2010][23134] (OC) Pending finalizers 0->0
[memdbg ][Wed May 26 12:31:38 2010][23134] Restarting of javathreads took 0.257 ms
*[gcpause][Wed May 26 12:31:38 2010][23134] Thread "pool-1-thread-1" id=217 idx=0x36c tid=25388 was in object alloc 75.397 ms from 1546.387 s*
[memdbg ][Wed May 26 12:34:04 2010][23134] GC reason: Other, cause: Memleak Request Data
[memdbg ][Wed May 26 12:34:04 2010][23134] Stopping of javathreads took 0.817 ms
[memdbg ][Wed May 26 12:34:04 2010][23134] old collection 38 started
[memdbg ][Wed May 26 12:34:04 2010][23134] Alloc Queue size before GC: 0, tlas: 0, oldest: 0
[memdbg ][Wed May 26 12:34:04 2010][23134] Compacting 1 heap parts at index 44 (type internal) (exceptional false)
The above log segment shows the tail of a GC which has just completed, then an object alloc delay for 75ms for thread "pool-1-thread-1", and then a subsequent GC kicks in much later which I believe is unrelated. I have a JRA trace from the test which shows that the object alloc latency event occurred almost a full second after the completion of the GC activity - something you can't see from the above trace which has second resolution in the timestamp.
What I'm unsure of is exactly how the object alloc delay can occur and then be rectified by the JVM outside of a GC. I understood the main cause of an object alloc latency event was that memory wasn't available (i.e. TLA does not have enough free space and a new TLA cannot be allocated) and that a GC would be required to free up memory to allow either a new TLA to be allocated or free up enough space in an existing one. We see an "object alloc" latency delay which follows the above pattern after every GC so I'm guessing it must somehow be related to the GC which has just finished, but I can't figure out how. My hope is to eliminate this kind of latency delay completely or at least down to single-figure ms delays.
Perhaps the deterministic GC means some memory reclaim is happening in parallel outside of the reported GC activity, but I'd be very surprised if this was the reason as surely the collector would be reporting it's activity more fully. It's been a while since I've looked this closedly at GC so I may have forgotten something.
Any help you can provide in working out how to address such latency spikes would be very helpful!
Thanks
Stuart

I think the extra time is due to the compaction of the heap (which occurs after a garbage collection).
Note also that a very low pausetarget can stress the garbage collector to less appreciated behavior, when the application and the hardware or not appropriate. If you look at the application about 30% live data or less at collection time is something your application should strive at. Running with more live data might break the deterministic behavior (depending on the hardware of course).
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Refer to http://otndnld.oracle.co.jp/document/products/jrockit/jrdocs/pdf/refman.pdf for more information.

Physical memory and paging

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abap/heaplimit           : Workprocess restart limit of heap memory
if helpful reward point is appreciated

Reading Lots of Objects into Memory

I need to read thousands of fairly large objects from an object database to the point that the JMV memory runs out.
A solution is to: read, use and discard as opposed to loading all the objects into memory at once -pretty simple but I want to do it right. I have a general idea on how to implement the approach but I need your help in locating some reading materials, code snipplets and/or best practices.
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If you're using thousands of objects you might look into the Flyweight Pattern (depending on what these objects are and what state they have). You might also look into increasing the amount of memory available to the JVM via that -Xms switch.
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Examples for SAP Memory and ABAP Memory

Hi all,
can u give me one example of sap memory and abap memory.
Ranjith

Hi,
SAP Memory
SAP memory is a memory area to which all main sessions within a SAPgui have access. You can use SAP memory either to pass data from one program to another within a session, or to pass data from one session to another. Application programs that use SAP memory must do so using SPA/GPA parameters (also known as SET/GET parameters). These parameters can be set either for a particular user or for a particular program at the time of logon using the SET PARAMETER statement. Other ABAP programs can then retrieve the set parameters using the GET PARAMETER statement. The most frequent use of SPA/GPA parameters is to fill input fields on screens .
example:
ABAP programs can access the parameters using the SET PARAMETER and GET PARAMETERstatements.
To fill one, use:
SET PARAMETER ID pid FIELD f
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To read an SPA/GPA parameter, use:
GET PARAMETER ID pid FIELD f.
This statement places the value stored under the pid ID into the variable f. If the system does not find any value for pid in the SAP memory, sy-subrc is set to 4. Otherwise, it sets the value to 0.
ABAP Memory
ABAP memory is a memory area that all ABAP programs within the same internal session can access using the EXPORT and IMPORT statements. Data within this memory area remains throughout a sequence of program calls, with the exception of LEAVE TO TRANSACTION. To pass data to a program that you are calling, the data needs to be placed in ABAP memory before the call is made from the internal calling session using the EXPORT statement. The internal session of the called program then replaces that of the calling program. The program called can then read from the ABAP memory using the IMPORT statement. If control is then returned to the program that made the initial call, the same procedure operates in reverse.If a transaction is called using LEAVE TO TRANSACTION, the ABAP memory and the call stack are deleted. They cannot be used for data transfer.
Since objects belonging to ABAP objects can only be accessed within an internal session, it does not make sense and is therefore forbidden (from a syntax point of view) to pass a reference to an object to a calling program through the ABAP memory.
Example:
Export hello to memory id 'Hello_world'.
Import hello from memory id 'Hello_world'
Regards
Sudheer

Releasing Objects from memory-Performance improvement

First Javafx was excellent in coding on UI rapidly. We did a image application and it was fine with some small memory tweaking pending. Since we have binded variables from static file to all objects, i think the memory of objects removed or deleted is not getting released. Is the there any way to unbind or destroy the objects which are binded. I think the the next release of Javafx will have a better performance.Any ideas or suggestions will help us to improve the performance drastically. Any help on this regard is highly appreciated. Thanks in advance.

Thanks Keap for your reply. Since we have used bind extensively, let me tell scenario the where we have used binding. We used a static class in javafx. Many variable in static class has been binded to javafx objects. Since the variable of javafx objects are binded to stastic varaibles, i doubt even after after not using the objects they are in the memory, because of the binding reference. since i dont have control of the static file scope, the objects are in memory and the app throws out of memory after sometime.We came forward with solution ie to use the conditional binding. I need other experts comments before proceeding as it needs lot of refactoring. I like to know whether the following statement
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As this issue blocking, we need a solution to improve it. Any help on this would be highly usefull.
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Object allocations, memory and UINavigationController

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