Bizzare thread blocks creating primitive arrays

Question

We recently had a situation where a production machine went down with a massive thread dump. It's resin webserver, and it gave 'Full thread dump Java HotSpot(TM) 64-Bit Server VM (14.0-b16 mixed mode):'.

There are a ton of BLOCKED threads, but they are confusing to me. IE, one is like:

"resin-8576" daemon prio=10 tid=0x00007f871827b800 nid=0x6b5 waiting for monitor entry [0x00007f864a7e6000]
   java.lang.Thread.State: BLOCKED (on object monitor)
        at java.lang.String.toCharArray(String.java:2725)
        at java.lang.Thread.setName(Thread.java:1051)
        at com.caucho.server.port.TcpConnection.run(TcpConnection.java:605)
        at com.caucho.util.ThreadPool$Item.runTasks(ThreadPool.java:730)
        at com.caucho.util.ThreadPool$Item.run(ThreadPool.java:649)
        at java.lang.Thread.run(Thread.java:619)

The code there is

char result[] = new char[count];

Another one is like

"resin-8574" daemon prio=10 tid=0x00007f8718277800 nid=0x6b3 waiting for monitor entry [0x00007f864a9e8000]
   java.lang.Thread.State: BLOCKED (on object monitor)
        at java.lang.String.valueOf(String.java:2840)
        at java.lang.Thread.getName(Thread.java:1061)
        at com.caucho.server.port.TcpConnection.run(TcpConnection.java:603)
        at com.caucho.util.ThreadPool$Item.runTasks(ThreadPool.java:730)
        at com.caucho.util.ThreadPool$Item.run(ThreadPool.java:649)
        at java.lang.Thread.run(Thread.java:619)

Where the code of String there is

return new String(data);

Those seem like strange places to be blocked.

Could anyone suggest a reason those calls would be blocking?

Thanks, -kal

It blocks on "new" so this could be caused by the internal memory management or garbage collector. It could be that you run out of memory (the out of memory exception is not allays thrown). — josefx, Mar 24 '11 at 17:16

score 2 · Accepted Answer · answered Mar 24 '11 at 17:13

It sounds like this method could be called alot and generate a lot of garbage. When the GC runs these methods whcih allocate objects could appear to be block while waiting for the GC.

I would try a more up to date JVM. e.g. Java 6 update 24 (which has JVM build 19 or 20) as you appear to have an older JVM.

Bizzare thread blocks creating primitive arrays

1 Answers1