Memory Leak in java with LinkedBlockingQuene

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Sun, 08 Jul 2007 02:50:22 -0700
Memory Leak in with LinkedBlockingQuene

    I have three questions which are memory leak and java GC concerned.


    I knew there must be some memory leaks in my program. I discovered
that the instances of LinkedBlockingQuene@Node,
LinkedBlockingQuene@Segment and others was increased continuously (By
JProfiler) and will not decrease even after all requests were
processed. First I thought if there were still some elements I forgot
to remove, then I checked all the LinkedBlockingQuene count and they
are all zero.

    I wanted to ask why @Node alive when the Quene is zero?

    BTW: I was a little puzzled by the LinkedBlockingQuene::clear()
    It just set head and last to null and if all the @Nodes in the
middle are alive after called it.

    I think Sun would not do such sunny thing, so why it work well?
     * Atomically removes all of the elements from this queue.
     * The queue will be empty after this call returns.
    public void clear() {
        try {
   = null;
        assert head.item == null;
        last = head;
            if (count.getAndSet(0) == capacity)
        } finally {


    The following content is Java GC concerned.

    After I had done some test for some time, the count of the @Node
instance was 1000 (for example), then I stopped sending any request to
my server, then the count of the @Node kept 1000. But when I did a
full gc (by Profiler), the count changed to 800 (for example) and kept
800 after many times full gc.

    My question is if the 200 instance can by free why JVM gc don't
free it in a idle time. If there are some error in my codes that VM
gc can't free it in a regular way and only can free it in Full GC.


    After I repaired the memory linked in my app. If Full GC (by VM or
not by call system.gc()) can by avoided?

    I assigned 2G memory for my java App. After 10~12 hours its memory
will reach about 2G and VM did Full gc automatically. The used memory
decrease to 1.4G but it cost 20s and during this time my app was
unresponsive which was not allowed.

    here is gc log:
    [GC 1963039KK->1663039K(2097152K), 0.0445726 secs]
    [Full GC 1963039K->1484445K(2097152K), 20.9461786 secs]

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