jinfo - Changing HotSpot VM Option

Java Tools Tutorials - Herong's Tutorial Examples

∟jinfo - Changing HotSpot VM Option

This section provides a tutorial example on how to set a new value to a HotSpot VM option on a given JVM process using the 'jinfo' tool.

The "jinfo" tool can be used to view the current value of any HotSpot VM option of a given JVM process as described in the previous section.

The "jinfo" tool can also be used set a new value of any HotSpot VM option using the "jinfo -flag name=value" format. Here is what I did to test this function with JDK on a Windows system:

herong> java -XX:MaxHeapSize=123456789 PrimeNumberSeeker 10 200
Period, Current int, # primes
1, 2, 0
2, 10, 4
...

(Start another command window.)
herong> jps -l -m
12724 jdk.jcmd/sun.tools.jps.Jps -l -m
15412 PrimeNumberSeeker 10 200

(View the current flag value)
herong> jinfo -flag MaxHeapSize 15412
-XX:MaxHeapSize=123731968

(Change the flag value)
herong> jinfo -flag MaxHeapSize=987654321 15412
Exception in thread "main" com.sun.tools.attach
   .AttachOperationFailedException:
   flag 'MaxHeapSize' cannot be changed
   at jdk.attach/sun.tools.attach.VirtualMachineImpl.execute(...
   at jdk.attach/sun.tools.attach.HotSpotVirtualMachine.executeCommand(...
   at jdk.attach/sun.tools.attach.HotSpotVirtualMachine.setFlag(...
   at jdk.jcmd/sun.tools.jinfo.JInfo.flag(JInfo.java:142)
   at jdk.jcmd/sun.tools.jinfo.JInfo.main(JInfo.java:123)