Hi !

I filled a ticket yesterday about a pb we face with many NIO framework, which I 
think could hit Tomcat too (see 
https://bz.apache.org/bugzilla/show_bug.cgi?id=63802). Actually, I think I'm 
facing this problem on a project I'm working on atm.

Remy suggested we discuss it on this mailing list.

Bottom line, what happens is that under some circumstances not well defined, 
the call to select() might end to an infinite loop eating all the CPU (select() 
returns 0, so select is immediately called again, and we loop).

In various NIO framworks - and being a MINA committer, I have implemented the 
discussed workaround -, we are controlling this situation by breaking this 
infinite loop this way :
- if the select() call returns 0
- then if we have called select() more than N times in less than M ms (N=10, 
M=100 in MINA)
- then we create a new Selector, register all the selectionKey that were 
registered on the broken selector, and ditch the old selector.

This workaround does not cost a lot when the selector works as designed, as a 
select() call should never return 0. 

I suggest Tomcat add such a workaround in the various versions (8 and 9 at 

Emmanuel Lécharny

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