Getting physical memory

[Chris]

Is it possible to know how much physical memory there is in a machine?

Runtime.getRuntime().totalMemory() returns the amount available to the JVM,
not the amount in a machine.

 

[Liz]

the dos command "mem" should do it
call it via NJI

 

[Jesper Nordenberg]

the dos command "mem" should do it
call it via NJI

"mem" only reports the memory available to DOS programs (for example
my 2k machine reports 1 MB of RAM). There are much better functions to
use in the Win32 API. Besides, the OP didn't write that he uses a
Windows machine.

There is no way to tell the amount of physical memory in pure Java.
Why do you need that information?

/Jesper Nordenberg

 

[Roedy Green]

"mem" only reports the memory available to DOS programs (for example
my 2k machine reports 1 MB of RAM). There are much better functions to
use in the Win32 API. Besides, the OP didn't write that he uses a
Windows machine.

If you can find any console mode app to tell you, exec it and capture
the result. See http://mindprod.com/jgloss/exec.html

 

[Roedy Green]

"mem" only reports the memory available to DOS programs (for example
my 2k machine reports 1 MB of RAM). There are much better functions to
use in the Win32 API. Besides, the OP didn't write that he uses a
Windows machine.

If you can find a WinApi call to tell you want you want, you can write
a tiny bit of JNI to get at it.
http://mindprod.com/jgloss/jni.html

See http://mindprod.com/products.html#PENTIUM for some sample JNI code
you could use as a model.

It might be part of the JConfig library. See
http://mindprod.com/jgloss/jconfig.html

 

[Liz]

If you can find a WinApi call to tell you want you want, you can write
a tiny bit of JNI to get at it.
http://mindprod.com/jgloss/jni.html

See http://mindprod.com/products.html#PENTIUM for some sample JNI code
you could use as a model.

It might be part of the JConfig library. See
http://mindprod.com/jgloss/jconfig.html

Ok, then figure out what the memory is using whatever and
provide it to the program via -D on the command line. The
program can get it through properties.

java -DMEMORY=55 myjavaprog

 

[Corey Brown]

"mem" only reports the memory available to DOS programs (for example
my 2k machine reports 1 MB of RAM). There are much better functions to
use in the Win32 API. Besides, the OP didn't write that he uses a
Windows machine.

[ SNIP ]

Ok, then figure out what the memory is using whatever and
provide it to the program via -D on the command line. The
program can get it through properties.

java -DMEMORY=55 myjavaprog

And if the Java program is long lived, then what?

 

[Liz]

On 8 Jun 2004 04:16:21 -0700, (e-mail address removed) (Jesper Nordenberg)
wrote or quoted :

"mem" only reports the memory available to DOS programs (for example
my 2k machine reports 1 MB of RAM). There are much better functions to
use in the Win32 API. Besides, the OP didn't write that he uses a
Windows machine.

[ SNIP ]

Ok, then figure out what the memory is using whatever and
provide it to the program via -D on the command line. The
program can get it through properties.

java -DMEMORY=55 myjavaprog

And if the Java program is long lived, then what?

What is your question?

 

[Chris]

There is no way to tell the amount of physical memory in pure Java.
Why do you need that information?

Because I want to use NIO's MappedByteBuffer to map files to memory. A
little experimentation shows that if you map too many files or files that
are too big you'll get error messages. So I want to know what the limits
are.

 

[Thomas Schodt]

Because I want to use NIO's MappedByteBuffer to map files to memory. A
little experimentation shows that if you map too many files or files that
are too big you'll get error messages. So I want to know what the limits
are.

You can set the limit.
Check the Evaluation section of:
<http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4879883>