Garbage collector and JVM

is garbage collector is part of JVM or it is part of our program process.
ie ... if we are having 3 programs running at the same time will we have one garbage collector for them or we will have 1 each ofor each process.
what is the priority of the garbage collector as a process.

GC is a part of JVM. GCs from different JVMs never
intersect.hmm.
So if i am having 3 programs of java running on one machine. how much JVM will i be running ... i guess one. so will they share one GC ???
what is the priority of GC at process level???

Similar Messages

Automatic Garbage collector after JVM almost hit max value on weblogic ?

Hi All,
I have application on weblogic 10MP2. I use 4G JVM. My application getting slow when the usage of JVM hit arround 70-80% of max heap size. Unfortunatelly, the garbage collector didn't run when it hit that high. So to keep my application in good state, I need to MANUALLY hit the Perform GC to keep the JVM below 70%.
Is there any settings to tell the JVM to perform GC when the free space of the JVM hit 30%?
What will the weblogic do if one of the server in warning state? There is a settings in the weblogic to specify when it hit some percentage of free space, it will bring the server to warning state. Will it do the Garbage Collector?
Need your help on this. I am tired of hitting the Perform GC button.
Really appeciate your help.
Thanks,
Eric

I am replying to my own post because I found a tool that
helped me solve in two hours what I had been stumped on
for the past few days.
The Heap Analysis Tool.
I had a major memory leak problem. I couldn't locate
the source until I downloaded and used this tool(for free).
This tool keeps track of memory used by objects,
each objects references, objects references by each
object, and all objects instances. All of this information
can be obtained in html format for efficient traversing
of object chains. I would highly recommend looking
this tool over if you intend on doing memory intensive
programming.
In case your curious where my error was I had two problems
which are now fixed. One. I had a couple of BufferedImages
that were leaking 30MB RAM. Two. I didn't know that using
ObjectStream's to read/write objects stored references
to the objects being written(preventing garbage collection).
Deffinately worth running the Heap Analysis Tool before
pointing a finger at System.gc().

Garbage Collector and verbose GC

Hi, we are getting strange behavior with the garbage collector if the verbosegc is enabled. The gc still report it is collecting memory but none is ever freed. If the option is not enabled the problem disapear. Has anyone experience something similar?
We are running on Sun 5.8 with weblogic 5.1 sp 8 and jdk 1.2.2_09

Can you post some of the verbosegc output? Output with -XX:+PrintGCDetails might
help a little more.

Garbage collector and JPEG decoder

Hi,
I have a problem with the garbage collector decoding JPEG images received on a TCP socket. The process works but each time that I have to decode an image I have to create a new decoder, this causes that the garbage collector starts to work constantly looking for memory. When the gc starts to work the streamed images almost stop since the gc takes all the process.
Here is the code that has the problem. On this code you can see that I create a new ByteArrayInputStream and a MediaTracker, but I know how reuse this objets, the problem is on the decoder.
Does any one have an idea of how to solve it?
Thanks
public void cargarImagen(Visualizador vision,
                              Cabecera cabImg,
                              boolean completa,
                              boolean grabar,
                              boolean pantCIF,
                              JFrame1 jf1)throws Exception{
        Visualizador aux;
        ByteArrayInputStream byis = new ByteArrayInputStream(s1.buffer);
        try{
                decoder=JPEGCodec.createJPEGDecoder(byis);
                try{
                       // decode
                                               vision.image_Webcam=decoder.decodeAsBufferedImage();
                }catch(ImageFormatException b){
                  System.out.println("Incorrect image format");
                }catch(Exception a){
                  System.out.println("Incorrect image");
                mediaTracker_track = new MediaTracker(vision);
                mediaTracker_track.addImage(vision.image_Webcam, 0);
             mediaTracker_track.waitForID(0,500);
        }finally{
                  byis.close();
        if(mediaTracker_track.statusID(0, false) == MediaTracker.COMPLETE){
              vision.repaint();
         else{    /* incorrect image */
              vision.image_Webcam = null;
              System.out.println("Discarded image");
}

I think that this is not the case. Images come from a TCP connection and the application start to read the next image from the socket when the previous one has been decoded and painted.
So, images are not stored on memory and the received images rate depens on how fast is the application reading images from the socket.
However, it is a good idea to start gc before getting next image, the average rate will decrease but it will avoid the "jumps" on visualization.

Force Garbage Collector calling

Hello
I have simple, static, single thread program. But it's a lot of memory demanding (large SortedSet, about one million items). After I finish working with this big SortedSet, I call "clear()" on it, for safe. Function uses this Set exits, and reference to this Set dies. Problem is, when this function exits, it's called multiple times again (same function), but unreferenced memory is still occupied, and heap usage grows and grows.
I need to force calling Garbage Collector and HALT MAIN PROCESS until GC refreshes all of unref. memory.
I tried calling "System.gc()" - without effect, parameter "-Xincgc" - without effect.
Thank you very much for help.
Pleas excuse my poor English, but I hope you understand me.
Tony (Czech Republic)

Why is this growing heap a problem, and why do you feel compelled to force gc?
Virtually all non-trivial applications experience growing and growing heap usage.
But the JVM should run gc when it is running out of memory anyway.
Did you get an OutOfMemoryError?
If you did, then you should review either your JVM heap settings, or in the worst case, your code. Your program may unintentionnally hold on to objects after being done with them (a java 'memory leak').
If you didn't get an OutOfMemoryError, then I suggest you don't worry about it.

Garbage collector don't works.

Hello people !
When I restart the weblogic server this do not shows the lastest change that I made. I think the problem is related to the garbage collector and its bean tree.
Do you known how to solve this?
Thank you.
Regards.

I'm working with WebLogic Server 10.0 and the problem is if I restart the server this don't holds the lastest change that I made, it happens with any type of change (deploy, undeploy, create or delete servers/services, etc).
I've reviewed the log file and I've found the following error:
<Jun 2, 2008 6:45:14 PM CDT> <Warning> <Management> <BEA-141269> <The temporary bean tree updateDeploymentContext(Mon Jun 02 10:46:11 CDT 2008) was allocated for an undo, get, or activate operation, but has not been garbage collected.>
Stopping PointBase server...
PointBase server stopped.
Thank you for your attention

Optimization of the JVM memory - Garbage Collector

Hi ,
Just a question about JVM memory management.
There is memory limitation of memory usage limitation (1.6M) in JVM.
Is there any possibility to use "Garbage collector" mechanism to optimize the memory usage?
Or any suggestions for the JVM memory optimization?
Thanks a lot!!!

nicolasmichael wrote:
Hi,
the "memory limitation" does not have anything to do with garbage collection, but with the address space your operating system provides. On a 32bit operating system, your virtual address space is limited to <= 4 GB, depending on your operating system (for example 1.something GB on Windows and 3.something GB on Solaris). No.
Windows 32 bit has a 2 GB application space and can be configured to allow a 3GB space.
The Sun VM does not allow more because of the way that the executable is linked.
[http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4358809]

Inefficient garbage collector process - WLS 8.1 SP6 - JVM jdk142_13 (SUN)

Hi all,
I am trying to perform some tuning operations in my server (maestroServer_01) because the application uses the total amount of heap size and the garbage collector process is not running fine. The arguments used on this VM are:
-server -Xms2048m -Xmx2048m -Xss512k -XX:PermSize=384m -XX:MaxPermSize=384m -XX:+UseParallelGC -XX:ParallelGCThreads=4 -XX:+UseAdaptiveSizePolicy -XX:NewRatio=8 -XX:SurvivorRatio=12 -Xverify:none -Xnoclassgc -XX:+DisableExplicitGC -XX:+PrintGCDetails -Dweblogic.webservice.i18n.charset=utf-8 -Duser.timezone=$JAVA_TZ -DejbURL='t3://localhost:9081' -DjpdURL='http://localhost:9081'
Please let me know if I can change these parameters in the WLS:
Services -> Bridge -> Messaging Bridge Thread Pool Size -> from 5 to 20
Configuration -> Tuning -> Socket Readers -> from 33 to 60, and disable "Enable Native IO" option.
I got some informations from internet about some parameters that can be used to improve the memory utilization of this JVM. The parameters are described in the link below:
http://java.sun.com/performance/reference/whitepapers/tuning.html
Does anyone know what can be done? The WLS needs to be restarted every day!
Thanks!

yes regularely .. :-) (as you can see from the posts..)
to your problem, the connectstring seems perfectly valid for a oracle light db installation (which we install within the bpel installation)
can you check if this polite process is running?
HTH clemens

Clear method and Garbage Collector

Hi Gurus,
Does the Clear method (hashtable, vector etc..) is a good option for garbage collection ?
In other words, if I have a vector V with 100 elements and I perform a V.clear(), am I sure that the 100 elements are now candidates for the Garbage Collection ?
Or is it better to write a loop performing a NULL assignment for each element of the vector ?

Hi schapel,
I know it's not a good idea to force the garbage collector, but let me explain what I am confronted with.
(FYI, I didn't write the source code. Comes from a 3rd party)
The aim is to build a jsp page which is the list of the files contained in a web server directory.
I have a "Directory" class, and a "File" class. To build the jsp, each directory of the webserver is represented by a directory class, and each file, ...by a file class.
To simplify, when the tree structure of the web server is build in memory, I create a jsp page to list the files, and then, I do not need the vector anymore. But the vector can be quite huge and each client will build his own vector at the begening of his session (and will never use it again during the session).
Don't you think it's usefull in that situation to free some memory ?

EMCC and Garbage Collector

We have 2 CUCM clusters connected via an ICT. We are migrating users from CM8.6 to CM10.5. During the migration we are changing Users AD attributes so that they disappear from CM8. As this marks the user as Inactive in CM8 (and deletes after 24hrs) this prevents the User from logging into CM10 with EMCC.
Is there a way around this?
ie force the garbage collector to run immediately and delete the user
or remove certain fields in CUCM 8 against the user so that they can login using CUCM10 credentials?
Thanks
Rich

I think you can do something clever here. You can convert the inactive user on cucm 8 back to a standard cucm user and then delete them. This way you can control when to remove the user instea dof waiting for garbage collection. You become your own garbage man :)
You can conver the users back to standard CUCM users using sql query update...Ths is easy to do
run sql update enduser set status=1 ( this is the general command to make all users standard cucm users..you don't want to run this..)
Use this command to make specific users active. You need to use the users extension to filter which user gets converted to standard cucm user
run sql update enduser set status=1 where telephonenumber like ‘2%’
This command will update users with extension beginning with 2
or
run sql update enduser set status=1 where telephonenumber = '2001'
This will convert user with extension 2001 to a standard cucm user
To make sure you got all the users you can use the command
run sql select * from enduser where status=0
This should return zero entry. If you find any user there then use the update command on those users

I have a memory leak, objective-c 2.0, and garbage collector...

the code i am using is a modification of the code/problem found in "Cocoa with Objective-C", chapter 3.
i have tried to use the objective-c 2.0 garbage collector methodology, using @property, @synthesize, etc. when i run the code as listed below i get a leaking message.
[Session started at 2008-02-01 23:33:37 -0500.]
2008-02-01 23:33:38.070 SongsFoundationTool[28876:10b] * _NSAutoreleaseNoPool(): Object 0x2040 of class NSCFString autoreleased with no pool in place - just leaking
Stack: (0x96b10178 0x96a3e0f8)
2008-02-01 23:33:38.075 SongsFoundationTool[28876:10b] Song 1: We Have Exposive
2008-02-01 23:33:38.076 SongsFoundationTool[28876:10b] * _NSAutoreleaseNoPool(): Object 0x2060 of class NSCFString autoreleased with no pool in place - just leaking
Stack: (0x96b10178 0x96a3e0f8)
2008-02-01 23:33:38.078 SongsFoundationTool[28876:10b] Song 2: Loops of Fury
The Debugger has exited with status 0.
when i include the commented out section, in the implementation file section, the description method, and use song1 and song2, in main, instead of song1.name and song2.name the program seems to run fine.
The Debugger has exited with status 0.
[Session started at 2008-02-01 23:38:24 -0500.]
2008-02-01 23:38:24.375 SongsFoundationTool[28936:10b] Song 1: We Have Exposive
2008-02-01 23:38:24.379 SongsFoundationTool[28936:10b] Song 2: Loops of Fury
The Debugger has exited with status 0.
please help me understand what's happening here.
also, why was it necessary to use
@property(copy, readwrite) NSString *name;
@property(copy, readwrite) NSString *artist;
instead of
@property(readwrite) NSString *name;
@property(readwrite) NSString *artist;
thanks everyone, the code is below.
// ....................... header file ...............
#import <Cocoa/Cocoa.h>
@interface Song : NSObject {
NSString *name;
NSString *artist;
@property(copy, readwrite) NSString *name;
@property(copy, readwrite) NSString *artist;
@end
//.................... the implementation file ..................
#import "Song.h"
@implementation Song
@synthesize name;
@synthesize artist;
-(NSString *) description
return [ self name ];
@end
//................................ main............................
#import <Foundation/Foundation.h>
#import "Song.h"
int main (int argc, const char * argv[]) {
Song *song1 = [ [ Song alloc ] init ];
song1.name= @"We Have Exposive" ;
[ song1 setArtist: @"The Future Sound Of Londown" ];
Song *song2 = [ [ Song alloc ] init ];
[ song2 setName: @"Loops of Fury" ];
[ song2 setArtist: @"The Chemical Brothers" ];
// Display Object
NSLog( @"Song 1: %@", song1.name );
NSLog( @"Song 2: %@", song2.name );
// include statements below if -description method is uncommented
// then comment out the two statements above. no memory leak if the code
// is used from the statements below and - description is not commented out and
// the two NSLog statements above are commented out.
NSLog( @"Song 1: %@", song1 );
NSLog( @"Song 2: %@", song2 );
return 0;
}

Normally, your main only has a call to NSApplicationMain(). If you aren't doing a traditional MacOS X application, you will still want at least NSApplicationLoad() to get enough of the runtime to avoid those messages.
I don't know for sure about the syntax of Objective-C 2.0. That stuff is all new. What error message are you getting that indicated that (copy, readwrite) is required? Could you provide a link to the actual example source? I did a quick check and assign and readwrite are the defaults. It is possible that readwrite by itself makes no sense. But I'm just guessing.

Swing components and the garbage collector

How much care does one need to take with swing components, with reference to running out of stack space? I ask because I'm writing a system for an automotive parts company, and the company tends to not reboot the machines very often...
Anyway... if a JFrame is closed, is it and all its components marked for GCing? Do I need to call the dispose method, or is this part of the default close behaviour? Or is there something else entirely?
Cheers

In class that calls for .setVisible(false) of one JFrame u MUST call
for dispose() method.
so
myFrame.setVisible(false)
myFrame.dispose()
myFrame = null // to help the garbage collector
If u have classes that becames from JFrame (or JDialog) u can
invoke in its constructors:
this.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE)
This makes uncecessary to call for dispose() method explicetly.
If u do not have this kind of classes u can invoke this method
after u have create your JFrame
JFrame myFrame = new JFrame();
myFrame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE)
The most important thing is REMOVE ALL LISETNERS that u have added, so, if u have classes that becames from JFrame u can ovverride
the dispose method to do that
eg
public void dispose()
super.dispose()
removeActionListener(.....)
and so on
If u do not have this kind of classes u must remove all listeners u have
added before u invoke the setVisible(false) method.
Regards

CORBA and garbage collector

Hi,
I�m writing a server with a method create(), which returns a new object supplying a home banking service for the clients.
My question is : when a given client has finished with the home banking object, do I need to call the gc, or is there an efficient one with CORBA (a kind of distributed garbage collector) ?
Thank you in advance

Maybe you heard about Distributed Garbage Collector (DGC)? Don't rely on this, since IIOP does not support this. Use PortableRemoteObject.unexportObject() to make remote objects that are no longer in use available for garbage collection.
Bert

How the protected finalize method is called by garbage collector

Dear All,
I have a double regarding the calling mechanism of finalize method. The access specifier of finalize method is protected, not only that if a class overrides this method then also the finalize method can be protected in the subclass of Object. But the concept of protected access specifier is, from outside of the package it can be accessed only from subclass.
The program (may be part of Garbage collector), which calls this (finalize) method mast not be in the same package (that is java.jang) nor it is a subclass of the class (whose finalize method it calls).
Then how the finalize method is getting called by the garbage collector when it is protected?
Regards,
Gourab

Refer to following link for the details
http://www.me.umn.edu/~shivane/blogs/cafefeed/2005/09/why-is-finalize-method-protected.html
The link gives answer to how a protected/private members are accessible to JVM or GC and why finalize is declared protected.

Logging Garbage collector for an OC4J with 2JVM

Hi, I have one OC4J with two JVM setted.
If I put -verbose:gc it logs in the std Output file.
I trying to log the garbage collector in two different file each one for one JVM.
Anyone as an idea?

Don't create massive amounts garbage memory. It's that simple. You should try to limit the creation of memory inside your animation loop. If there is a process inside the loop that creates memory, there is definitely some way to create that item staticly, rather than allocating new memory with each iteration. There shouldn't be any kind of problem that would involve the creation of THIS much memory, and it's deallocation. If you read about how the garbage collector is implemented, you'll notice that it stores all of it's memory on a single conveyor belt. This is for ALL memory in the program. Therefor once the garbage collector has gone through and marked all of the memory that needs to be reclaimed, it performs it's sweep and must feeze the entire program because that conveyor belt can not be manipulated while it's re-arranging the memory. The garbage collector will eliminate MOST memory leaks, but it does not eliminate any thought on the part of the programmer about memory.
-Jason Thomas.

Garbage collector and JVM

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