Name: agR10195 Date: 01/28/2004



Alexey Gibadullin, ###@###.###

The following test reveals that MemoryPoolMBean.setCollectionUsageThreshold(0)
method throws IllegalArgumentException, if max value of the pool is 0.

import java.util.*;
import java.lang.management.*;

public class Test {
    public static void main(String[] argv) {
        List poolsMBean = ManagementFactory.getMemoryPoolMBeans();
        
        for (int i = 0; i < poolsMBean.size(); i++) {
            MemoryPoolMBean pool = (MemoryPoolMBean) poolsMBean.get(i);
            long threshold;
            
            System.out.println("\n" + i + ": " + pool.getName() + " "
                             + pool.getUsage());
            
            if (!pool.isCollectionUsageThresholdSupported()) {
                System.out.println("CollectionUsageThreshold is not supported");
                continue;
            }
            
            long max = pool.getUsage().getMax();
            
            if (max != 0) {
                System.out.println("Max value is not 0");
                continue;
            }
            System.out.println("Max value is 0");
            
            try {
                pool.setCollectionUsageThreshold(0);
            } catch (Exception e) {
                e.printStackTrace(System.out);
            }
        }
    }
}

% ../jdk1.5.0-b35/solaris-sparc/bin/java Test

0: Code Cache init = 163840(160K) used = 594816(580K) committed = 622592
(608K)max = 33554432(32768K)
CollectionUsageThreshold is not supported

1: Eden Space init = 2097152(2048K) used = 217152(212K) committed = 2097152
(2048K)max = -1(-1K)
Max value is not 0

2: Survivor Space 1 init = 65536(64K) used = 0(0K) committed = 65536 (64K)max =
-1(-1K)
Max value is not 0

3: Survivor Space 2 init = 65536(64K) used = 0(0K) committed = 65536 (64K)max =
0(0K)
Max value is 0
java.lang.IllegalArgumentException: Invalid threshold: 0 > max (0).
        at
sun.management.MemoryPoolImpl.setCollectionUsageThreshold(MemoryPoolImpl.java:18
4)
        at Test.main(Test.java:29)

4: Tenured Gen init = 1441792(1408K) used = 0(0K) committed = 1441792 (1408K)max
= 59703296(58304K)
Max value is not 0

5: Perm Gen init = 8388608(8192K) used = 1433152(1399K) committed = 8388608
(8192K)max = 67108864(65536K)
Max value is not 0

The spec for setCollectionUsageThreshold(long) says:

    void setCollectionUsageThreshold(long threhsold)
    
    Sets the collection usage threshold of this memory pool to the given
    threshold value. When this threshold is set to positive, the Java
    virtual machine will check the memory usage at its best appropriate
    time after it has expended effort in recycling unused objects in this
    memory pool.
    
    Parameters: threhsold - the new collection usage threshold value in bytes.
                Must be non-negative.

    Throws: IllegalArgumentException - if limit is negative or greater than the
                                          ^^^^^
            maximum amount of memory that this memory pool can use.


1. There is no variable "limit" mentioned in the spec. The similar specification
   for setUsageThreshold says:
   
   Throws: IllegalArgumentException - if threshold is negative or greater than
           the maximum amount of memory that this memory pool can use.
           
   So, it looks like a misprint in setCollectionUsageThreshold(long):
   "threshold" sould be read instead of "limit".
   
2. Concerning that, IllegalArgumentException should not be thrown for
   threshold=0, since it is not "greater than the maximum amount of memory
   that this memory pool can use" (max).
   
   Similiar bug was found in MemoryUsage() constructor:

       4979453 sun.management.MemoryPoolImpl.getCollectionUsage() throws IAE
               (max=0)
   
One more minor misprint is in MemoryPoolMBean.getUsage().toString():

    init = 2097152(2048K) used = 217152(212K) committed = 2097152
    (2048K)max = -1(-1K)
    
It looks like a space " " is missed before "max" substring.

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