Name: js5519 Date: 02/05/99


Either the value returned by Runtime.getFreeMemory() is
extremely inaccurate, or the runtime does not manage
memory correctly when a large number of small objects
are allocated.

The following class accepts one argument, the number of
objects to allocate. When executed it will print out
the amount of memory available after each allocation.

The application is started with a fixed heap size

java -mx4m -ms4m -verbosegc Gctest7 200000

The application throws a java.lang.OutOfMemory error when
the percentage of free memory is significantly larger than
0 (more than 20% of the memory is available, depending on
the JDK).

This problem occurs with the following JDKs

NT 1.1.6 (with or without the updated JIT)
NT 1.2
    NT 4.0
    java -fullversion -> JDK-1.2-V
    the runtime reports 46% of the memory is free

Solaris 1.1.6
    Solaris 2.6
    Solaris_JDK_1.1.6_04
    the runtime reports that 38% of the memory is free

The problem does not occur with Solaris_JDK_1.2_01_dev06_fcsV.
When that version is used the runtime reports that 0% of the
memory is available before the OutOfMemoryError is thrown.

public class Gctest7 {
    static long totalMem;
    static long freeMem;
    static int pFree;
    static double pctFree;
    static int count;
    static Object[] objArray;
    static Integer max;

    public static void main(String[] args) {
        max = Integer.valueOf(args[0]);
try {
test();
} catch(Throwable thr) {
System.err.println("Caught " + thr.getClass().getName());
System.err.println(thr.getMessage());
thr.printStackTrace();
System.err.println("FAILED: " + pFree + "% free " +
" total = " + totalMem +
" free = " + freeMem +
" count = " + count);
}
    }

    static void test() {
        objArray = new Object[max.intValue()];
count = 0;

        for (int i = 0; i < max.intValue(); i++) {
freeMem = Runtime.getRuntime().freeMemory();
totalMem = Runtime.getRuntime().totalMemory();
pctFree = (double) freeMem / (double) totalMem;
pFree = (int) (100.0 * pctFree);
System.err.println("DATA: " + pFree + "% free " +
" total = " + totalMem +
" free = " + freeMem +
" count = " + count);
objArray[i] = new byte[2];
count++;
}
    }

}
(Review ID: 48819)
======================================================================

Output from jdk1.1.7
======================
TA: 19% free total = 4194296 free = 810888 count = 84510
DATA: 19% free total = 4194296 free = 809848 count = 84511
DATA: 19% free total = 4194296 free = 808472 count = 84512
<GC: managing allocation failure. need 16 bytes, type=2, action=1>
<GC: freed 18604 objects, 952176 bytes in 112 ms, 52% free (1758544/3355440)>
  <GC: init&scan: 1 ms, scan handles: 87 ms, sweep: 24 ms, compact: 0 ms>
<GC: managing allocation failure. need 16 bytes, type=2, action=2>
<GC: managing allocation failure. need 16 bytes, type=2, action=3>
<GC: managing allocation failure. need 16 bytes, type=2, action=4>
<GC: tried to expand handle space over limit>
<GC: managing allocation failure. need 16 bytes, type=2, action=5>
<GC: totally out of heap space>
Caught java.lang.OutOfMemoryError
java.lang.String
java.lang.OutOfMemoryError: java.lang.String
at java.lang.StringBuffer.toString(StringBuffer.java)
at Gctest7.test(Gctest7.java:74)
at Gctest7.main(Gctest7.java:26)
FAILED: 19% free total = 4194296 free = 807432 count = 84513

/usr/local/java/jdk1.1.7/solaris/bin/java
illium%

Output with jdk1.1.8
============================
<GC: 10 milliseconds since last GC>
<GC: freed 2 objects, 1040 bytes in 106 ms, 47% free (1609176/3355440)>
  <GC: init&scan: 1 ms, scan handles: 90 ms, sweep: 15 ms, compact: 0 ms>
<GC: managing allocation failure: need 1032 bytes, type=2, action=2>
<GC: 110 milliseconds since last GC>
<GC: managing allocation failure: need 1032 bytes, type=2, action=3>
<GC: 1 milliseconds since last GC>
<GC: managing allocation failure: need 1032 bytes, type=2, action=4>
<GC: 12 milliseconds since last GC>
<GC: managing allocation failure: need 40 bytes, type=2, action=1>
<GC: 9 milliseconds since last GC>
<GC: freed 1 objects, 1016 bytes in 106 ms, 47% free (1609160/3355440)>
  <GC: init&scan: 1 ms, scan handles: 89 ms, sweep: 16 ms, compact: 0 ms>
<GC: managing allocation failure: need 40 bytes, type=2, action=2>
<GC: 110 milliseconds since last GC>
<GC: managing allocation failure: need 40 bytes, type=2, action=3>
<GC: 0 milliseconds since last GC>
<GC: managing allocation failure: need 40 bytes, type=2, action=4>
<GC: 12 milliseconds since last GC>
illium%

Output with HotSpot alpha2
========================
 3967K->3967K(4032K+0K), 0.4400000 secs]
, 0.6100000 secs]
[Full GC[phase 1, 0.1200000 secs]
[phase 2, 0.1200000 secs]
[phase 3, 0.1700000 secs]
[phase 4, 0.0000000 secs]
Restoring 338 marks
 3967K->3967K(4032K+0K), 0.4300000 secs]
[Full GC[phase 1, 0.1300000 secs]
[phase 2, 0.1200000 secs]
[phase 3, 0.1800000 secs]
[phase 4, 0.0000000 secs]
Restoring 338 marks
 3967K->3967K(4032K+0K), 0.4300000 secs]
Symbol: 'vm exception holder'#
# HotSpot Virtual Machine Error, Should Not Reach Here Error
#
# ShouldNotReachHere()
#
/usr/re/hotspot/src/solaris_only/hotspot_beta1_hp/build/solaris/../../src/share/vm/runtime/deoptimization.cpp, 207#
#
# Error happend during: deoptimize frame
#
illium%
/usr/local/java/jdk_hotspot/solaris_alpha2/bin/java
illium%