[jboss-jira] [JBoss JIRA] (JGRP-1881) TimeService: provide time on request

[Bela Ban (JIRA)]

Bela Ban created JGRP-1881:
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             Summary: TimeService: provide time on request
                 Key: JGRP-1881
                 URL: https://issues.jboss.org/browse/JGRP-1881
             Project: JGroups
          Issue Type: Enhancement
            Reporter: Bela Ban
            Assignee: Bela Ban
             Fix For: 3.6


Currently the TimeService registers a task that runs every (say) 500 ms. It gets the current time and updates a field. Threads which get the time from the TimeService get the value of that field, so {{System.currentTimeMillis()}} is not called too much.
However, when no thread needs to get the time for a period of time, the TimeService nevertheless calls {{System.currentTimeMillis()}} every 500 ms, and we have an additional task in the time.

h5. SOLUTION
* Remove that task which periodically gets the current time
* Add a {{timestamp}} field ({{System.nanoTime()}}) which gets set when {{System.currentTimeMillis()}} is called
* Add a field {{current_time}} which is set by {{System.currentTimeMillis()}}
* When a thread wants to get the current time from the TimeService, it compares the current time with the timestamp and, if 500 ms have elapsed, calls {{System.currentTimeMillis()}}, sets the timestamp and current_time fields and returns the time
* If the time elapsed since the last update is less than 500 ms, it returns {{current_time}}

There has to be synchronization around getting the current time ({{System.currentTimeMillis()}}), but this could be done with a CAS and a busy loop.



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