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https://issues.apache.org/jira/browse/HTTPCORE-773?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17902769#comment-17902769
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Anithamahalakshmi commented on HTTPCORE-773:
--------------------------------------------
Thank you [~olegk] for the super quick response. What are your thoughts on
having a selector which chooses with the IO Worker thread with the least amount
of individual pending requests to serve or let the IO worker threads poll for
requests as they become available. The latter will ensure if there is a thread
is stuck for whatever reason, it will never get assigned more requests.
> Safeguard against blocked IOWorker thread
> -----------------------------------------
>
> Key: HTTPCORE-773
> URL: https://issues.apache.org/jira/browse/HTTPCORE-773
> Project: HttpComponents HttpCore
> Issue Type: Improvement
> Components: HttpCore NIO
> Reporter: Anithamahalakshmi
> Priority: Major
> Fix For: 5.4-alpha1
>
>
> # During the initialisation of ApacheAsyncClient, a single main thread is
> created -
> [https://github.com/xSke/CoreServer/blob/master/src/org/apache/http/impl/nio/client/CloseableHttpAsyncClientBase.java#L40.]
> # This IO reactor thread does two key jobs: 1) It internally instantiate IO
> dispatcher threads once They never stop either. They keep polling for new IO
> event) and 2) It then works as a daemon (which never stops) to process new
> events. It worth to notice that all events IO reactor thread is connection
> related event per
> https://github.com/wso2/wso2-httpcore-nio/blob/master/modules/httpcore-nio/src/main/java/org/apache/http/impl/nio/reactor/DefaultConnectingIOReactor.java#L164
> # For http request which needs a new IO connection, IO reactor thread is
> invoked to create such IO connection asynchronously -
> [https://github.com/wso2/wso2-httpcore-nio/blob/master/modules/httpcore-nio/src/main/java/org/apache/http/nio/pool/AbstractNIOConnPool.java#L427]
> Connection pending to be created in such asynchronous process is reported as
> {{pending}} connection in Apache connection status.
> # In such asynchronous process, connection to be created is added into
> {{requestQueue}} -
> [https://github.com/wso2/wso2-httpcore-nio/blob/master/modules/httpcore-nio/src/main/java/org/apache/http/impl/nio/reactor/DefaultConnectingIOReactor.java#L251].
> {{requestQueue}} is later on polled by IO reactor thread as a daemon, and
> established channel should be handed off to IO dispatcher thread via
> following logic
> -[https://github.com/wso2/wso2-httpcore-nio/blob/master/modules/httpcore-nio/src/main/java/org/apache/http/impl/nio/reactor/DefaultConnectingIOReactor.java#L276].
> It is interesting to notice that which IO dispatcher thread such new channel
> should be handed off to is based on round-robin per
> [https://github.com/wso2/wso2-httpcore-nio/blob/master/modules/httpcore-nio/src/main/java/org/apache/http/impl/nio/reactor/AbstractMultiworkerIOReactor.java#L475.]
>
> # The IO dispatcher thread is expected to pull and process new IO event
> assigned to it by selector, and then process assigned new channel as well per
> [https://github.com/wso2/wso2-httpcore-nio/blob/master/modules/httpcore-nio/src/main/java/org/apache/http/impl/nio/reactor/AbstractIOReactor.java#L222]
> However if a certain IO dispatcher thread is blocked while some previous
> processing, it goes undetected and new requests+connection pair keep getting
> assigned to the blocked thread which is unable to process the request and
> release the connection back to the pool, eventually we exhaust the max
> connection possible from the pool and cause availability drop.
>
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