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From Patricia Shanahan <p...@acm.org>
Subject TaskManager thread limit
Date Wed, 28 Jul 2010 17:42:57 GMT
In addition to a limit related to the number of runnable tasks, a 
TaskManager has a hard limit on the number of threads it will create.

The parameterless constructor has limit 10, and most other uses have 
compile time limits in the range of 10 to 15 threads.

com.sun.jini.reggie.RegisrarImpl has a compile time limit of 50 threads.

com.sun.jini.mahalo.TxnManagerImpl creates two pools, settlerpool and 
taskpool. The settlerpool has limit 150 threads. The taskpool has limit 
50 threads.

Even 150 threads could be low in a large server, especially if the 
threads are used to wait for anything, so that each thread does not need 
a hardware thread for a significant fraction of its life.

As noted in the NIO vs. IO discussion that Peter pointed out, the key to 
getting good performance simply is to take advantage of the fact that an 
idle thread is a cheap, simple way to remember the state of some activity.

There is one approach that would minimize the number of changes but 
increase flexibility. We could redefine the maximum thread count as 
being the maximum number of threads per X, where X is a measure of 
system size with a minimum of 1, but increasing on large systems.

X could be based on the number of processors, the maximum heap memory, 
or some combination.


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