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From Filip Hanik - Dev Lists <devli...@hanik.com>
Subject Re: svn commit: r1051539 - /tomcat/trunk/java/org/apache/tomcat/util/threads/CounterLatch.java
Date Wed, 29 Dec 2010 02:17:39 GMT


On 12/28/2010 5:02 PM, sebb wrote:
> On 22 December 2010 16:04, Filip Hanik - Dev Lists<devlists@hanik.com>  wrote:
>> On 12/21/2010 7:29 PM, sebb wrote:
>>>> -    private long signal;
>>>> +    private volatile long signal;
>>> It would be cheaper to make it final as it's only ever set in the ctor
>>> and is immutable.
>> nothing cheaper, volatile are only expensive to write, not read.
> That's not my understanding of how volatile works.
there is a great book on concurrency that explains how the bus and cpu architectures handle
these, if I remember the title of it, I will 
send it to you
> AIUI, the reader thread always needs to refresh the value of the field
> in case another thread has updated it.
>
> Whereas a final field can be safely cached in local memory.
>
>> If maxConnections becomes a dynamically adjustable attribute, so will this one
>> have to be.
> True, but at present it is immutable.
>
>>>>      private volatile boolean released = false;
>>>>
>>>>      /**
>>>>
>>>>
>>>>
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