Caldarale, Charles R wrote:
From: André Warnier [mailto:a...@ice-sa.com]
Subject: Re: CLOSE_WAIT and what to do about it
If these sockets disappear during a GC, then it must mean that they are
still being referenced by some "abandoned" objects sitting on the Heap,
which have not yet been reclaimed by the GC.
Which probably means that the objects in question have gone out of
scope, before the socket they used was properly close()'d.
Your analysis looks reasonable to me. There are some analysis tools that will
examine a live heap (or dump thereof) and find the reachable and unreachable
objects; jhat is a free one that comes with JDK 6:
http://java.sun.com/javase/6/webnotes/trouble/TSG-VM/html/tooldescr.html#gblfj
Allright, I have done that too.
I generated a Heap dump using
jmap -heap:format=b <pid>
That gave me file heap.bin of some 4.5 MB.
I then used the jhat program to open it.
jhat launches itself by default as a webserver on port 7000, which you
can access using a normal browser.
That's where my problem starts however, because being a mere Java
fiddler I don't really know what I am looking at, and what to look for.
I did a lot of guesswork anyway, and using my knowledge of the
application more than the links, I came upon the name of a class that
looks like it is reponsible for opening/closing the sockets that remain
in CLOSE_WAIT.
I found the following function in the class :
public void close()
throws SomeException
{
putEndRequest();
flush();
socket = null;
}
flush() being another function which reads the socket until there's
nothing left to read, and throws away the result.
"socket" is a property of the object created by this class, obtained
somewhere else from a java.net.Socket object.
Looking at that code above, it is obvious that "socket" is open, until
it is set to null, without previously doing a socket.close().
I don't know Java enough to know if this alone could cause that socket
to be lingering until the GC, but I kind of suspect so.
How does a Java expert look at that ?
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