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From "Jose Dillet (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HTTPASYNC-86) Race condition in async client when a keep alive connection is reused in POST request method
Date Wed, 17 Dec 2014 15:15:13 GMT

    [ https://issues.apache.org/jira/browse/HTTPASYNC-86?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14249961#comment-14249961
] 

Jose Dillet commented on HTTPASYNC-86:
--------------------------------------

I don't follow the last comment, #connectionAllocated is invoked for both requests: first
one which creates a fresh new connection, and second one which obtains the connection from
the pool.

The log shows the connection was active after ConnectionClosedException is throws, and was
closed only after shutting down the client.

> Race condition in async client when a keep alive connection is reused in POST request
method
> --------------------------------------------------------------------------------------------
>
>                 Key: HTTPASYNC-86
>                 URL: https://issues.apache.org/jira/browse/HTTPASYNC-86
>             Project: HttpComponents HttpAsyncClient
>          Issue Type: Bug
>    Affects Versions: 4.0.2, 4.1-beta1
>         Environment: Ubuntu 12.04 64 bits Kernel 3.2.0-74
>            Reporter: Jose Dillet
>         Attachments: AsyncClientRaceConditionSample.java, httpasyncclient-test.log
>
>
> I have found a race condition in the async client when a POST request reuses a keep alive
connection. We have around 2%-4% of our runs in a Continuous Integration environment failing
because of this issue.
> I have found a consistent way of forcing the failure by using a debugger, so I can force
the events to happen in the order which uncovers the problem.
> I have tested it on httpasyncclient 4.0.2 / httpcore 4.3.2 and httpasyncclient 4.1-beta1
/ httpcore 4.4-beta1 and it happens in both versions (the lines provided in the steps to reproduce
are from version 4.0.2).
> How to reproduce:
> 1) Add these breakpoints:
> a - DefaultClientExchangeHandlerImpl:304
> b - DefaultClientExchangeHandlerImpl:168
> 2) Run AsyncClientRaceConditionSample sample program
> Processing first request:
> -  Program hits breakpoint a -> Resume
> -  Program hits breakpoint b -> Resume
> Processing second request:
> - Program hits breakpoints a and b (in different threads)
> - Resume a)
> - Resume b)
> (Probably adding a small sleep after DefaultClientExchangeHandlerImpl:303 only for the
testing would also uncover the issue).
> ConnectionClosedException is thrown with this stack trace:
> Exception in thread "main" java.util.concurrent.ExecutionException: org.apache.http.ConnectionClosedException:
Connection closed
> 	at org.apache.http.concurrent.BasicFuture.getResult(BasicFuture.java:68)
> 	at org.apache.http.concurrent.BasicFuture.get(BasicFuture.java:77)
> 	at AsyncClientRaceConditionSample.process(AsyncClientRaceConditionSample.java:81)
> 	at AsyncClientRaceConditionSample.main(AsyncClientRaceConditionSample.java:45)
> Caused by: org.apache.http.ConnectionClosedException: Connection closed
> 	at org.apache.http.impl.nio.client.DefaultClientExchangeHandlerImpl.connectionAllocated(DefaultClientExchangeHandlerImpl.java:305)
> 	at org.apache.http.impl.nio.client.DefaultClientExchangeHandlerImpl.access$000(DefaultClientExchangeHandlerImpl.java:63)
> 	at org.apache.http.impl.nio.client.DefaultClientExchangeHandlerImpl$1.completed(DefaultClientExchangeHandlerImpl.java:360)
> 	at org.apache.http.impl.nio.client.DefaultClientExchangeHandlerImpl$1.completed(DefaultClientExchangeHandlerImpl.java:357)
> 	at org.apache.http.concurrent.BasicFuture.completed(BasicFuture.java:115)
> 	at org.apache.http.impl.nio.conn.PoolingNHttpClientConnectionManager$InternalPoolEntryCallback.completed(PoolingNHttpClientConnectionManager.java:465)
> 	at org.apache.http.impl.nio.conn.PoolingNHttpClientConnectionManager$InternalPoolEntryCallback.completed(PoolingNHttpClientConnectionManager.java:449)
> 	at org.apache.http.concurrent.BasicFuture.completed(BasicFuture.java:115)
> 	at org.apache.http.nio.pool.AbstractNIOConnPool.fireCallbacks(AbstractNIOConnPool.java:443)
> 	at org.apache.http.nio.pool.AbstractNIOConnPool.lease(AbstractNIOConnPool.java:276)
> 	at org.apache.http.impl.nio.conn.PoolingNHttpClientConnectionManager.requestConnection(PoolingNHttpClientConnectionManager.java:261)
> 	at org.apache.http.impl.nio.client.DefaultClientExchangeHandlerImpl.requestConnection(DefaultClientExchangeHandlerImpl.java:351)
> 	at org.apache.http.impl.nio.client.DefaultClientExchangeHandlerImpl.start(DefaultClientExchangeHandlerImpl.java:126)
> 	at org.apache.http.impl.nio.client.InternalHttpAsyncClient.execute(InternalHttpAsyncClient.java:129)
> 	at org.apache.http.impl.nio.client.CloseableHttpAsyncClient.execute(CloseableHttpAsyncClient.java:72)
> 	at org.apache.http.impl.nio.client.CloseableHttpAsyncClient.execute(CloseableHttpAsyncClient.java:102)
> 	at org.apache.http.impl.nio.client.CloseableHttpAsyncClient.execute(CloseableHttpAsyncClient.java:87)
> 	at AsyncClientRaceConditionSample.process(AsyncClientRaceConditionSample.java:80)
> 	... 1 more
> Some analysis from my side:
> 1 - When the first request is processed, this is the execution order of relevant lines
(and the thread where it is processed):
> a - (I/O dispatcher 1) DefaultClientExchangeHandlerImpl<T>.connectionAllocated(NHttpClientConnection)
line: 303
> b - (I/O dispatcher 1) DefaultClientExchangeHandlerImpl<T>.connectionAllocated(NHttpClientConnection)
line: 304
> c - (I/O dispatcher 1) CPoolProxy.detach() line: 60
> d - (I/O dispatcher 1) DefaultClientExchangeHandlerImpl<T>.responseCompleted()
line: 168
> 2 - When the second request is processed c) might happen before b) which leads to the
problem:
> a - (main) DefaultClientExchangeHandlerImpl<T>.connectionAllocated(NHttpClientConnection)
line: 303
> c - (I/O dispatcher 1) CPoolProxy.detach() line: 60
> b - (main) DefaultClientExchangeHandlerImpl<T>.connectionAllocated(NHttpClientConnection)
line: 304
> e - (main) BasicFuture<T>.failed(Exception) line: 122
> d - (I/O dispatcher 1) DefaultClientExchangeHandlerImpl<T>.responseCompleted()
line: 168
> The problem is that in case 2 the connection can be closed before request is completed
because a) is processed in main thread and c) is processed in I/O dispatcher thread, so the
ordering b < c is not guaranteed.
> However in case 1 because all the events are processed in I/O dispatcher thread, the
ordering b < c is guaranteed (this seems to be true even if there are several dispatcher
threads).



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