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  1. HttpComponents HttpAsyncClient
  2. HTTPASYNC-79

Connection leak due to race condition on keep-alive boundary

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      Description

      We are experiencing a race condition between:

      1. I/O dispatcher closing a connection due to keep-alive expiry

      2. PoolingNHttpClientConnectionManager leasing the same connection

      Consider valid exchange 1 provided below:

      2014.07.07 08:01:59.282 org.apache.http.impl.nio.conn.PoolingNHttpClientConnectionManager DEBUG [HLAPI-52] PoolingNHttpClientConnectionManager:245 Connection request: [route: {}->http://10.250.32.140:8082][total kept alive: 1; route allocated: 7 of 1000; total allocated: 7 of 5000]
      2014.07.07 08:01:59.283 org.apache.http.impl.nio.conn.PoolingNHttpClientConnectionManager DEBUG [HLAPI-52] PoolingNHttpClientConnectionManager$InternalPoolEntryCallback:462 Connection leased: [id: http-outgoing-20156][route: {}->http://10.250.32.140:8082][total kept alive: 0; route allocated: 7 of 1000; total allocated: 7 of 5000]
      2014.07.07 08:01:59.283 org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionImpl DEBUG [HLAPI-52] LoggingIOSession:164 http-outgoing-20156 10.252.152.177:61023<->10.250.32.140:8082[ACTIVE][r:r]: Set attribute http.nio.exchange-handler
      2014.07.07 08:01:59.285 org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionImpl DEBUG [I/O dispatcher 61] LoggingIOSession:141 http-outgoing-20156 10.252.152.177:61023<->10.250.32.140:8082[ACTIVE][rw:w]: Set timeout 20000
      2014.07.07 08:01:59.285 org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionImpl DEBUG [HLAPI-52] LoggingIOSession:102 http-outgoing-20156 10.252.152.177:61023<->10.250.32.140:8082[ACTIVE][rw:r]: Event set [w]
      2014.07.07 08:01:59.286 org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionImpl DEBUG [I/O dispatcher 61] LoggingIOSession:102 http-outgoing-20156 10.252.152.177:61023<->10.250.32.140:8082[ACTIVE][rw:w]: Event set [w]
      2014.07.07 08:01:59.286 org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionImpl DEBUG [I/O dispatcher 61] LoggingIOSession$LoggingByteChannel:201 http-outgoing-20156 10.252.152.177:61023<->10.250.32.140:8082[ACTIVE][rw:w]: 1111 bytes written
      2014.07.07 08:01:59.287 org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionImpl DEBUG [I/O dispatcher 61] LoggingIOSession:109 http-outgoing-20156 10.252.152.177:61023<->10.250.32.140:8082[ACTIVE][r:w]: Event cleared [w]
      2014.07.07 08:01:59.688 org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionImpl DEBUG [I/O dispatcher 61] LoggingIOSession$LoggingByteChannel:186 http-outgoing-20156 10.252.152.177:61023<->10.250.32.140:8082[ACTIVE][r:r]: 8443 bytes read
      2014.07.07 08:01:59.690 org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionImpl DEBUG [I/O dispatcher 61] LoggingIOSession$LoggingByteChannel:186 http-outgoing-20156 10.252.152.177:61023<->10.250.32.140:8082[ACTIVE][r:r]: 8140 bytes read
      2014.07.07 08:01:59.690 org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionImpl DEBUG [I/O dispatcher 61] LoggingIOSession$LoggingByteChannel:186 http-outgoing-20156 10.252.152.177:61023<->10.250.32.140:8082[ACTIVE][r:r]: 8190 bytes read
      2014.07.07 08:01:59.691 org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionImpl DEBUG [I/O dispatcher 61] LoggingIOSession:109 http-outgoing-20156 10.252.152.177:61023<->10.250.32.140:8082[ACTIVE][:r]: Event cleared [r]
      2014.07.07 08:01:59.692 org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionImpl DEBUG [HLAPI-52] LoggingIOSession:102 http-outgoing-20156 10.252.152.177:61023<->10.250.32.140:8082[ACTIVE][r:r]: Event set [r]
      2014.07.07 08:01:59.693 org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionImpl DEBUG [I/O dispatcher 61] LoggingIOSession$LoggingByteChannel:186 http-outgoing-20156 10.252.152.177:61023<->10.250.32.140:8082[ACTIVE][r:r]: 8124 bytes read
      2014.07.07 08:01:59.693 org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionImpl DEBUG [I/O dispatcher 61] LoggingIOSession$LoggingByteChannel:186 http-outgoing-20156 10.252.152.177:61023<->10.250.32.140:8082[ACTIVE][r:r]: 0 bytes read
      2014.07.07 08:01:59.694 org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionImpl DEBUG [I/O dispatcher 61] LoggingIOSession:109 http-outgoing-20156 10.252.152.177:61023<->10.250.32.140:8082[ACTIVE][:r]: Event cleared [r]
      2014.07.07 08:01:59.695 org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionImpl DEBUG [HLAPI-52] LoggingIOSession:102 http-outgoing-20156 10.252.152.177:61023<->10.250.32.140:8082[ACTIVE][r:r]: Event set [r]
      2014.07.07 08:01:59.695 org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionImpl DEBUG [HLAPI-52] LoggingIOSession:102 http-outgoing-20156 10.252.152.177:61023<->10.250.32.140:8082[ACTIVE][r:r]: Event set [r]
      2014.07.07 08:01:59.696 org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionImpl DEBUG [HLAPI-52] LoggingIOSession:102 http-outgoing-20156 10.252.152.177:61023<->10.250.32.140:8082[ACTIVE][r:r]: Event set [r]
      2014.07.07 08:01:59.697 org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionImpl DEBUG [I/O dispatcher 61] LoggingIOSession$LoggingByteChannel:186 http-outgoing-20156 10.252.152.177:61023<->10.250.32.140:8082[ACTIVE][r:r]: 0 bytes read
      2014.07.07 08:01:59.697 org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionImpl DEBUG [I/O dispatcher 61] LoggingIOSession$LoggingByteChannel:186 http-outgoing-20156 10.252.152.177:61023<->10.250.32.140:8082[ACTIVE][r:r]: 0 bytes read
      2014.07.07 08:01:59.698 org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionImpl DEBUG [I/O dispatcher 61] LoggingIOSession:171 http-outgoing-20156 10.252.152.177:61023<->10.250.32.140:8082[ACTIVE][r:r]: Remove attribute http.nio.exchange-handler
      2014.07.07 08:01:59.699 org.apache.http.impl.nio.conn.PoolingNHttpClientConnectionManager DEBUG [I/O dispatcher 61] PoolingNHttpClientConnectionManager:279 Releasing connection: [id: http-outgoing-20156][route: {}->http://10.250.32.140:8082][total kept alive: 0; route allocated: 7 of 1000; total allocated: 7 of 5000]
      2014.07.07 08:01:59.699 org.apache.http.impl.nio.conn.PoolingNHttpClientConnectionManager DEBUG [I/O dispatcher 61] PoolingNHttpClientConnectionManager:293 Connection [id: http-outgoing-20156][route: {}->http://10.250.32.140:8082] can be kept alive for 5.0 seconds
      2014.07.07 08:01:59.700 org.apache.http.impl.nio.conn.PoolingNHttpClientConnectionManager DEBUG [I/O dispatcher 61] PoolingNHttpClientConnectionManager:299 Connection released: [id: http-outgoing-20156][route: {}->http://10.250.32.140:8082][total kept alive: 1; route allocated: 7 of 1000; total allocated: 7 of 5000]
      

      Connection id=20156 has been used for communication, returned to the PoolingNHttpClientConnectionManager (and underlying AbstractNIOConnectionPool). The connection may be kept alive for 5 seconds.

      Now analyze the second provided exchange using the same connection:

      2014.07.07 08:02:04.689 org.apache.http.impl.nio.conn.PoolingNHttpClientConnectionManager DEBUG [HLAPI-60] PoolingNHttpClientConnectionManager:245 Connection request: [route: {}->http://10.250.32.140:8082][total kept alive: 1; route allocated: 7 of 1000; total allocated: 7 of 5000]
      2014.07.07 08:02:04.690 org.apache.http.impl.nio.conn.PoolingNHttpClientConnectionManager DEBUG [HLAPI-60] PoolingNHttpClientConnectionManager$InternalPoolEntryCallback:462 Connection leased: [id: http-outgoing-20156][route: {}->http://10.250.32.140:8082][total kept alive: 0; route allocated: 7 of 1000; total allocated: 7 of 5000]
      2014.07.07 08:02:04.691 org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionImpl DEBUG [I/O dispatcher 61] LoggingIOSession$LoggingByteChannel:186 http-outgoing-20156 10.252.152.177:61023<->10.250.32.140:8082[ACTIVE][r:r]: -1 bytes read
      2014.07.07 08:02:04.691 org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionImpl DEBUG [HLAPI-60] LoggingIOSession:164 http-outgoing-20156 10.252.152.177:61023<->10.250.32.140:8082[ACTIVE][r:r]: Set attribute http.nio.exchange-handler
      2014.07.07 08:02:04.692 org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionImpl DEBUG [I/O dispatcher 61] LoggingIOSession:115 http-outgoing-20156 10.252.152.177:61023<->10.250.32.140:8082[ACTIVE][r:r]: Close
      2014.07.07 08:02:04.692 org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionImpl DEBUG [HLAPI-60] LoggingIOSession:102 http-outgoing-20156 10.252.152.177:61023<->10.250.32.140:8082[ACTIVE][rw:r]: Event set [w]
      

      Notice the time difference between exchanges being about 5 seconds.

      1. At the keep-alive boundary, the connection is requested and leased from the PoolingNHttpClientConnectionManager.

      2. Then, the I/O Dispatcher with id=61, which performed previous exchange, attempts to read from the connection, receiving no data (-1 bytes).

      3. In the meantime, HLAPI-60 thread that requested the connection, sets the http.nio.exchange-handler attribute.

      4. However the connection is already recognized as 'dead' by the I/O dispatcher and is then closed.

      5. In the end, the PoolingNHttpClientConnectionManager prepares to write to the connection. This is the last activity for connection id=20156. It is never released to the connection pool.

      We use Http Components in conjunction with CXF and in the end get a SocketTimeoutException from Async Transport:

      Caused by: java.net.SocketTimeoutException: Read Timeout
              at org.apache.cxf.transport.http.asyncclient.AsyncHTTPConduit$AsyncWrappedOutputStream.getHttpResponse(AsyncHTTPConduit.java:614)
              at org.apache.cxf.transport.http.asyncclient.AsyncHTTPConduit$AsyncWrappedOutputStream.getResponseCode(AsyncHTTPConduit.java:699)
              at org.apache.cxf.transport.http.HTTPConduit$WrappedOutputStream.handleResponseInternal(HTTPConduit.java:1555)
              at org.apache.cxf.transport.http.HTTPConduit$WrappedOutputStream.handleResponse(HTTPConduit.java:1525)
              at org.apache.cxf.transport.http.HTTPConduit$WrappedOutputStream.close(HTTPConduit.java:1330)
              ... 25 common frames omitted
      

      This scenario is non-deterministic. There are about 10-15 connections leaked this way from the connection pool of 1000 each day. The connection pool slowly degrades and in the end requires a restart of the whole component. Our solution is suppose to be HA, so this is a major problem for us and for our business client.

      We have also noticed, that:

      1. If the connection is reused earlier (i.e. after 3-4 seconds), there is no read attempt from the I/O dispatcher that causes the '-1' result in the negative scenario. Connection is used to perform a valid exchange and may be further kept alive. Maybe it is a matter of setting the 'http.nio.exchange-handler' attribute before the I/O dispatcher attempts to read from connection due to keep-alive timeout?

      2. Also, if around the keep-alive time boundary the connection is not reused, it does not leak from the connection pool (it is never leased after being closed by the I/O dispatcher).

      The negative scenario occurs only if there is an interleave between the I/O dispatcher closing the connection and the connection being leased from PoolingNHttpClientConnectionManager at the keep-alive boundary - about 5 seconds in our case.

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            • Assignee:
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              Reporter:
              poltarzewski Przemysław Ołtarzewski
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