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From Christopher Schultz <ch...@christopherschultz.net>
Subject Re: Question about thread's "keep alive time" value in Embed Tomcat 8.5 in Spring Boot 1.5
Date Fri, 01 Nov 2019 13:46:30 GMT
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Roy,

On 11/1/19 08:23, Roy Zhang wrote:
> I am confused about "keep alive time" value in Embed Tomcat. I am
> using Spring Boot 1.5, embed tomcat version is 8.5.
> 
> According to
> https://github.com/spring-projects/spring-boot/issues/16450#issuecomme
nt-480236238,
>
> 
we can't configured thread's "keep alive time" via "maxIdleTime"
> parameter, "keep alive time" value is hard coded as 60s via
> https://github.com/apache/tomcat/blob/de1f55e672106031821948d5cac80f40
adc09513/java/org/apache/tomcat/util/net/AbstractEndpoint.java#L884,

It
> 
is only hard-coded if you use the internal, default Executor. You
can instantiate your own Executor with whatever settings you wish.

It's a bad name for that setting, but this is how long "excess"
threads will live when they are not being used.

> I found 60s "keep alive time" sometimes take effect, some times it 
> doesn't take effect. Could u please kindly help to review my
> following two cases and kindly provide explanation? Really
> appreciate ur help in advance!
> 
> *Case 1 (60s "keep alive time" DOESN'T take effect):* API latency:
> _100ms_ Test step: run API with 800 concurrent threads for 1
> minutes, then run API with 10 concurrent threads for about 1 hour.
> As we can see from following graph, after BusyThreads reduced from
> ~800 to 10, CurrentThreadsCount remains at 800 for following 1 hour
> (60s "keep alive time" DOESN'T take effect). After test stopped,
> CurrentThreadsCount reduced from 800 to 100(MinSpareThreads). 
> image.png

Your images have been stripped from the mailing list. Find another way
to describe your problem.

When you say "X concurrent threads", how often are requests being
made? Constantly? So you are sending requests as fast as possible with
c=10?

I haven't read the code in detail, but I'm guessing that the thread
pool uses a queue and not a stack of threads, so each thread gets
used, repeatedly, in order of availability. That means that if you
keep making requests, you'll keep hitting *all* the threads in the
queue and not just the same 10 over and over again. So they never time
out.

> *Case 2 (60s "keep alive time" DOES take effect):* API latency:
> _10s_ Test step: run API with 800 concurrent threads for 1 minutes,
> then run API with 10 concurrent threads for about 1 hour. As we can
> see from following graph, after BusyThreads reduced from ~800 to 
> 10, CurrentThreadsCount reduced from 800 to 100(MinSpareThreads).
> 60s "keep alive time" DOES take effect)

Note that Tomcat's thread pool is just a wrapper around Java's
ThreadPoolExecutor -- adding methods to handle Tomcat's lifecycle
events, etc.

So if the pool isn't behaving as you'd like it, you'll need to file a
but against the Java API and not Tomcat.

- -chris
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