r*****l
发帖数: 2859 | 1 I got conflicting answers online. I think it should be stored in permgen
space since the variable is part of the class definition.
What's your opinion? |
g**e
发帖数: 6127 | 2 vote for permgen
【在 r*****l 的大作中提到】
: I got conflicting answers online. I think it should be stored in permgen
: space since the variable is part of the class definition.
: What's your opinion?
|
b******y
发帖数: 9224 | 3 I did some research. It seems to me that static variables, if they are
primitives, are stored in permgen, also object references.
Objects could be allocated in any heap. |
r*****l
发帖数: 2859 | 4 This is inline with what I thought. Thanks.
Now there is something more interesting. If I have a class Singleton, look
at the code below:
private static final Singleton instance_ = new Singleton();
Suppose reference to the Singleton class (value of "instance_") is stored in
permgen, then what about the Singleton object. It has the same life cycle
as instance_ so it makes sense to store it in permgen. However, I do believe
they will be stored in normal heap (finally tenured) cause otherwise the
permgen may become very congested with normal objects there.
【在 b******y 的大作中提到】
: I did some research. It seems to me that static variables, if they are
: primitives, are stored in permgen, also object references.
: Objects could be allocated in any heap.
|
g**e
发帖数: 6127 | 5 Storing the object in heap makes sense. But a full collection will clean
perm gen too.
in
believe
【在 r*****l 的大作中提到】
: This is inline with what I thought. Thanks.
: Now there is something more interesting. If I have a class Singleton, look
: at the code below:
: private static final Singleton instance_ = new Singleton();
: Suppose reference to the Singleton class (value of "instance_") is stored in
: permgen, then what about the Singleton object. It has the same life cycle
: as instance_ so it makes sense to store it in permgen. However, I do believe
: they will be stored in normal heap (finally tenured) cause otherwise the
: permgen may become very congested with normal objects there.
|
r*****l
发帖数: 2859 | 6 I know that but generally permgen size is quite small compared to normal
heap so it makes sense to store as less data as possible.
【在 g**e 的大作中提到】
: Storing the object in heap makes sense. But a full collection will clean
: perm gen too.
:
: in
: believe
|
r*****l
发帖数: 2859 | 7 Although my understanding is like yours, I have not found concrete evidence
to support this. Do you have a link?
【在 b******y 的大作中提到】
: I did some research. It seems to me that static variables, if they are
: primitives, are stored in permgen, also object references.
: Objects could be allocated in any heap.
|
g**e
发帖数: 6127 | 8 不一定呀，如果有的程序需要大量操作字符串，perm gen还是需要适当调整一下的
【在 r*****l 的大作中提到】
: I know that but generally permgen size is quite small compared to normal
: heap so it makes sense to store as less data as possible.
|
r*****l
发帖数: 2859 | 9 In normal case, production system may have >1.5G Xmx. And 256M PermSize is
large enough.
This is always case by case however.
【在 g**e 的大作中提到】
: 不一定呀，如果有的程序需要大量操作字符串，perm gen还是需要适当调整一下的
|
b******y
发帖数: 9224 | 10
evidence
Sorry, no.
I read several sites online, but none of the sites could give definitive
answer. I guess it is just per VM implementation maybe.
But, your question about the "dangling" reference in the permgen sounds
interesting I guess maybe the java vm has some way to keep track of that?
I guess what I would do in that case, before garbage collect any object from
the heap, I would check if that object is referenced by any from the
permgen.
Maybe a question for Oracle ;-)
【在 r*****l 的大作中提到】
: Although my understanding is like yours, I have not found concrete evidence
: to support this. Do you have a link?
|
r*****l
发帖数: 2859 | 11 Read the JVM Specs. All field metadata is stored in the permgen (method area
). Static variable each has a reference to a ConstanceValue data structure,
also in permgen. The value can be of type long, float, double, int (short,
char, etc.), and string. The Specs does not specify how a object reference
is stored (or at least I did not find it). Maybe it's like this: if the type
of the field is not primitive, then the value stored in the ConstantValue
data structure is interpreted as an object reference?
from
【在 b******y 的大作中提到】
:
: evidence
: Sorry, no.
: I read several sites online, but none of the sites could give definitive
: answer. I guess it is just per VM implementation maybe.
: But, your question about the "dangling" reference in the permgen sounds
: interesting I guess maybe the java vm has some way to keep track of that?
: I guess what I would do in that case, before garbage collect any object from
: the heap, I would check if that object is referenced by any from the
: permgen.
|
k******p
发帖数: 21 | 12 perm generation as part of meta data of classes, methods. |
r*****l
发帖数: 2859 | 13 This is too vague and most people know it.
My two specific questions are:
1, If static variable is stored in permgen
2, Proof whether the answer is yes or no.
【在 k******p 的大作中提到】
: perm generation as part of meta data of classes, methods.
|
