Unexpected empty selected list

shreyaspurohit

Hi,

I am getting the below message on the server. Please let me know what it means.

09.Apr.09 09:59:48,135 < WARN> Unexpected empty selected list (76 times in last 16 ms)

Thanks,
Shreyas

Dario Crivelli

The Server issues this warning when a java NIO "select" call returns with nothing selected.
This is possible only in particular conditions, but it should not happen in a general case.

As long as a few calls experience this outcome, this is less than a problem. Under a heuristic threshold, no warn is prompted.
If more occurrences happen, as in your case (76 times in 16 ms), this can be a waste of CPU, but still not a problem.
We keep an eye open on this phenomenon, because "select" is called in a loop, but we are confident that the NIO implementation will not allow a strict loop of "select" calls returning nothing.

Alessandro Alinone

Hi Shreyas,

What Java version are you using exactly? And on which operating system?

shreyaspurohit

Hi Dario,

I get these messages a lot, continuously for some time, and then it stops.

@ Alessandro,

I am running on JDK 1.6.0_07.

Thanks,
Shreyas

Alessandro Alinone

Shreyas,

Are you using Linux?

Is "76 times in last 16 ms" the highest number of occurrences you had?

We report such statistical info in the log because there is a known bug in Sun's implementation of Java NIO for Linux, which Lightstreamer can work around. Only if much higher numbers of occurrences of empty selectors are reported, it makes sense to activate the workaround.

Cheers,
Alessandro