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Update TestScheduler.cs #5011

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May 14, 2021
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Update TestScheduler.cs #5011

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8 changes: 6 additions & 2 deletions src/core/Akka.TestKit/TestScheduler.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -88,10 +88,14 @@ private void InternalSchedule(TimeSpan? initialDelay, TimeSpan delay, ICanTell r
{
var scheduledTime = _now.Add(initialDelay ?? delay).UtcTicks;

if (!_scheduledWork.TryGetValue(scheduledTime, out var tickItems))
ConcurrentQueue<ScheduledItem> tickItems;
while (!_scheduledWork.TryGetValue(scheduledTime, out tickItems))
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so this is compare-and-swap basically @brah-mcdude ?

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Ah ok, I think I get this now after reading the original issue on #5010

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@brah-mcdude brah-mcdude May 13, 2021 •
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tickItems is a queue of all the items that we want to schedule for a specific scheduledTime tick.
We need to extract this queue from the dictionary of all _scheduledWork.
If TryGetValue fails, then we need to create tickItems and add it to _scheduledWork.
However, if by the time that we call TryAdd, someone else has already added a new tickItems at the scheduledTime tick entry, our call to TryAdd will fail. In such a scenario - we need to start over.
In other words, we need to loop while TryGetValue fails.
Actually, our thread's SECOND attempt to TryAdd MUST ALWAYS succeed.
So, theoretically, we could re-write it as a 3 iterations for loop: (int i = 0; i < 3; i++) that will throw an exception if i reaches 2.

{
tickItems = new ConcurrentQueue<ScheduledItem>();
_scheduledWork.TryAdd(scheduledTime, tickItems);
if (_scheduledWork.TryAdd(scheduledTime, tickItems))
{
break;
}
}

var type = message == null ? ScheduledItem.ScheduledItemType.Action : ScheduledItem.ScheduledItemType.Message;
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