I discovered using Axis in tomcat causes a memory leak.
It seems using threadlocal in the classes causes a memory leak for each Call
that is created. Threadlocal sticks around until the calling thread dies, and
since tomcat keeps threads alive to answer new calls, the threadlocal data
never goes away. The Call object gets stuck in the threadlocal data, which
contains the entire soap response and all objects. This is a BIG memory leak.
I initially cleared it by forcing all Call objects to clean their member vars
after I was done with a call, then I realized the source was from the thread
local class. Here is some info I found about threadlocal:
This is stated in the Sun Javadocs for ThreadLocal:
Each thread holds an implicit reference to its copy of a
ThreadLocal as long as the thread is alive and the
ThreadLocal object is accessible; after a thread goes
away, all of its copies of ThreadLocal variables are
subject to garbage collection (unless other references
to these copies exist).
So, this means that ANY APPLICATION that uses PreparedStatements in a thread
that 1) either does a lot of PreparedStatements or 2) never dies (i.e., a
main thread) will ALWAYS eventually have an out of memory error. Simply put,
this is a MEMORY LEAK. I imagine that the leak is very small, the
ThreadLocal object only contains one member variable, maybe 64 bytes or less
(depending on the VM implementation). So, our 60,000 PreparedStatements of 2
ThreadLocals each times 64 bytes (my wild guess) is 7.5MB.
Ideas? I've never used threadlocal myself so this is new to me.