[jboss-jira] [JBoss JIRA] (JGRP-1553) TimeScheduler3

[Bela Ban (JIRA)]

    [ https://issues.jboss.org/browse/JGRP-1553?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12741862#comment-12741862 ] 

Bela Ban commented on JGRP-1553:
--------------------------------

The above code looks similar to what ScheduledThreadPoolExecutor does (with DelayQueue/PriorityQueue). Also, after the simplications of NAKACK{2} and UNICAST{2}, we won't have many tasks in a timer.
Therefore I'll do the following:
#1 Either fix the above problems in TimeScheduler2 directly, or write a new TimeScheduler3 to do that
#2 default back to timer_type="old". This uses the DefaultTimeScheduler, which intenally uses ScheduledThreadPoolExecutor. This is probably good enough, as we won't have many tasks in the timer.
                
> TimeScheduler3
> --------------
>
>                 Key: JGRP-1553
>                 URL: https://issues.jboss.org/browse/JGRP-1553
>             Project: JGroups
>          Issue Type: Enhancement
>            Reporter: Bela Ban
>            Assignee: Bela Ban
>             Fix For: 3.3
>
>
> The current TimeScheduler2 class has a few deficiencies:
> - taskReady() should only set next-execution-time if its argument is less than next-execution-time
> - no_tasks: when setting this CAS, the result is only checked in 1 location, but not the other
> - Potential loss of task: when calling schedule() on an existing Entry (same execution time), and - before adding the task to Entry - Entry is removed by _run() as it was executed, then the newly added task will never get to run !
> - Simplification: instead of headMap(), just use firstEntry(), removeFirstEntry(). See pseudo code below.
> As a workaround, timer_type="old" will switch back to the previous default timer. The reason for TimeScheduler3 (versus changing TimeScheduler2) is that we can simply switch to the new impl by setting (a new) timer_type="new2". Should this have a bug, we can simply switch back to "new" or "old" (or "wheel".
> Over time, TimeScheduler2 will get removed.
> Pseudo code:
> * loop while has tasks
> ** get the first task
> ** if its time is less than the current time: execute it and remove it
> ** else block (on the next task or 10s) until an element is added

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