RE: finalize(), System.runFinalization(), System.gc();

I have found System.gc() useful in special circumstances where there is
a natural place for garbage collection to occur. By "natural place" I
mean at a point in repeated process which is repeated which leaves a lot
of stuff to clean up prior to the next repetition of the process.

For example I have an image display program "hooked" to a 5250 session.
The "cycle is"
- user does something which selects an image
- load and display image
- user does data entry from image into 5250 session which causes
a lot of image manipulation such as showing different regions of
interest (and leaves a lot of stuff to clean up)
- user finishes the data
Cycle repeats

When the Java program relied on the system to do GC the image (Java)
application would freeze for several seconds every so often (18 to 22
images) while the system cleaned up.

By putting a call to System.gc() before "load and display image" seems
to improve the overall performance. I suspect that the call to
System.gc() "suggests" that this is a good time to collect garbage and
the JVM uses the opportunity while waiting on IO in the load and display
part.

Bill Blalock



-----Original Message-----
From: java400-l-bounces@xxxxxxxxxxxx
[mailto:java400-l-bounces@xxxxxxxxxxxx] On Behalf Of James Perkins
Sent: Monday, March 09, 2009 3:39 PM
To: Java Programming on and around the iSeries / AS400
Subject: Re: finalize(), System.runFinalization(), System.gc();

I should have noted too, this is from the Sun documentation. I'm sure
the
IBM GC operates the same way though.
--
James R. Perkins


On Mon, Mar 9, 2009 at 13:02, James Perkins <jrperkinsjr@xxxxxxxxx>
wrote:

Read the documentation on Object.finalizer(), it's not guaranteed to

run.

http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Object.html#finalize()
<http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Object.html#finalize%
28%29>

Also, System.gc() does not run the GC, it merely suggests to the JVM

that

it will run.

http://java.sun.com/j2se/1.4.2/docs/api/java/lang/System.html#gc()<http:
//java.sun.com/j2se/1.4.2/docs/api/java/lang/System.html#gc%28%29>

Keep in mind this will not clean up objects that still have

references.

It's possible to have arrays that have been decreased in size to still

have

references if not done properly. Also, check any listeners or timer

jobs and

make sure they are using WeakReference collections.
--
James R. Perkins



On Mon, Mar 9, 2009 at 12:02, Lim Hock-Chai

<Lim.Hock-Chai@xxxxxxxxxxxxxxx

wrote:

Is there a guideline on when should an application manually calls the
finalize(), System.runFinalization(), or System.gc()? Or should
application never calls these methods and let the JVM mangement it on
its own?

thanks
--
This is the Java Programming on and around the iSeries / AS400

(JAVA400-L)

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