NPE from java

Question

we are seeing npe when we spawn con. threads and try to place values in a treemap
java.lang.NullPointerException
     at java.lang.Long.compareTo(Long.java:923)
     at java.lang.Long.compareTo(Long.java:34)
     at java.util.TreeMap.cmp(TreeMap.java:2273)
     at java.util.TreeMap.get(TreeMap.java:2189)
     at java.lang.Thread.run(Thread.java:619)
this used to work in 1.6.0_11 but once we change to the later version of jvm 1.6.0_20 it fails with above error
we add debug it works fine in update 20 too... this is a startup servlet
OS -solaris-sparcv9
Edited by: user13115160 on Dec 9, 2010 3:43 PM
Edited by: user13115160 on Dec 10, 2010 12:39 PM

Answer 1

As someone already mentioned, you may have coded things not quite right for them to be thread safe and while the newer jvm exploits the specifications (and memory model) more to achieve higher performance, your problem surfaces.
In case you used hand-crafted synchronization on the TreeMap, I think you can quickly find out whether you did that right by temporarily switching to a synchronized Map as suggested by the TreeMap documentation:
>
If no such object exists, the map should be "wrapped" using the Collections.synchronizedSortedMap method. This is best done at
creation time, to prevent accidental unsynchronized access to the map:
SortedMap m = Collections.synchronizedSortedMap(new TreeMap(...));
Assuming that this synchronization (done by pros ;-)) is correct and a test run does not yield the same errors, you may want to revise your handcrafted sync code.