NIO.2 and GC fragmentation

[Alan Bateman]

Mark Thornton wrote:
> Java direct buffers aren't allocated from the Java heap (the buffer 
> itself that is, not the object which wraps it)! They are allocated 
> using the OS runtime and don't affect the garbage collector. The JVM 
> has limit (default 64MB I seem to recall) of total direct buffer 
> allocation. What can be a problem is disposing of them --- the memory 
> is released by a cleanup thread after the object has become 
> unreachable. However you can run short of memory for direct or memory 
> mapped buffers, while still having plenty of free space in the Java heap.
That's right although the maximum is tied to the maximum size of the 
java heap (and may be configured via the -XX:MaxDirectMemorySize option).

-Alan.