How long are resources used (file descriptor and memory) for Java temporary files (jar_cache####.tmp)?

Question

I"m running a Java application on a Linux system. I noticed that the application seemed to consume a lot of file handles (I get "Too many open files" after a few days).

So when I use the 'lsof' command to dump all the files associated with the Java application, I get something like this:

java  2690  root  239u  REG  3,2  428057  94300 /tmp/jar_cache5782499018536796385.tmp (deleted)
java  2690  root  240u  REG  3,2  58955   94360 /tmp/jar_cache3818842806647031366.tmp (deleted)
java  2690  root  241u  REG  3,2  28673   94301 /tmp/jar_cache8793213887943479521.tmp (deleted)
java  2690  root  242u  REG  3,2  67115   94302 /tmp/jar_cache3648070144390426051.tmp (deleted)

I'm only showing 4 here, but there are actually 87 of them and the number grows in time.

From what I've read online, Java uses these temporary files internally or something and they are normal.

As the output above says, they are deleted, and I confirm that they do not exist physically on the file system.

But what I'm afraid of is that it's not releasing the file descriptors or any of the associated memory... does anyone know anything about these '/tmp/jar_cache####.tmp' files or have experience with these?

Answer 1

The /tmp/jar_cache files are produced when loading a jar via a URLClassloader. I suspect there are components of the application that are being reloaded and this results in old jar_cache files being deleted and new ones created. The fact that file handles are not released seems like a JVM issue though - I've seen this behavior as well with the same JDK version.

There are comments along these lines on this JVM bug: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4166799

although the issue was closed a while ago.