Sergiu Prodan updated HTTPCORE-433:
    Attachment: threads_when_inactivity_set_to_1.png

Thread visualisation when making requests from 10 different threads. 
PoolingHttpClientConnectionManager#setValidateAfterInactivity set to 1

> Setting validateAfterInactivity to 1ms increases lock contention in 
> AbstractConnPool
> ------------------------------------------------------------------------------------
>                 Key: HTTPCORE-433
>                 URL: https://issues.apache.org/jira/browse/HTTPCORE-433
>             Project: HttpComponents HttpCore
>          Issue Type: Bug
>          Components: HttpCore
>    Affects Versions: 4.4.4
>            Reporter: Sergiu Prodan
>         Attachments: httpclient_thread_dump, 
> threads_when_inactivity_set_to_1.png
> This issue was observed after upgrading to httpclient v4.5.2 and httpcore 
> v4.4.4. 
> When configuring the PoolingHttpClientConnectionManager, I have set 
> validateAfterInactivity to 1ms as this is the only way of maintaining the old 
> behaviour, i.e. checking every connection if is stale before using it.
> I have observed a performance degradation under high load when the httpclient 
> is shared between multiple threads. 
> After taking a thread dump, one thing that got my attention was several 
> threads waiting for same ReentrantLock instance while trying to 
> AbstractConnPool#getPoolEntryBlocking/AbstractConnPool#release. The 
> ReentrantLock instance in question was owned by another thread performing 
> CPool#validate.
> It seems to me that performing this stale check inside the region protected 
> by this lock is unnecessary and also induces a big performance hit when using 
> the httpclient from multiple threads.
> I've atached a thread dump of a test application that reproduces this 
> behaviour. ReentrantLock in question in this thread dump is 
> 0x0000000706e8b9a8 and is owned by Thread-4

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