Java HotSpot Virtual Machine

I'm getting a thread deadlock, but when I active the 1.4.1 thread deadlock detection utility, it only reports that the (deadlocked) thread is waiting for monitor entry. The line reported is just a simple synchronized (obj) { ... } block. No other thread is reported as having locked the obj, and the deadlock detection utility does not report a Java level deadlock.

The problem is intermittently reproducible. Does anyone know of a way to determine what thread is holding the monitor in question? I've poked around with jswat to no avail.

Should it even be possible to be waiting enter a monitor that is not held by another thread?

OS is RH Linux 7.2, JDK 1.4.1.

Following is the thread trace for the deadlocked thread (full trace available upon request):

"Resin cached servlet thread" daemon prio=1 tid=0x0x83fabc8 nid=0x2d17 waiting f
or monitor entry [55784000..55784840]
at com.livecluster.core.plugin.LiveCacheClientManager.updateClients(Live
CacheClientManager.java:98)
- waiting to lock <0x4589b920> (a java.util.HashMap)
at com.livecluster.servlet.LiveCacheServlet.put(LiveCacheServlet.java:25
2)
at com.livecluster.servlet.LiveCacheServlet.service(LiveCacheServlet.jav
a:128)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:103)
at com.caucho.server.http.FilterChainServlet.doFilter(FilterChainServlet
.java:82)
at com.caucho.server.http.Invocation.service(Invocation.java:288)
at com.caucho.server.http.ServletServer.serviceTop(ServletServer.java:93
7)
at com.caucho.server.http.HttpRequest.handleRequest(HttpRequest.java:213
)
at com.caucho.server.http.HttpRequest.handleConnection(HttpRequest.java:
158)
at com.caucho.server.TcpConnection.run(TcpConnection.java:140)
at java.lang.Thread.run(Thread.java:536)