Question

I have a multithreaded java program that runs on Amazon’s EC2. It queries and fetches data items from a vendor via HttpPost and HttpGet, using a org.apache.http.impl.client.DefaultHttpClient. Concurrently, it pushes the retrieved data items into S3 using AWS’s Java SDK.

After a few days of running, I get the symptoms that normally come with http connection leaks:

org.apache.http.conn.ConnectionPoolTimeoutException: Timeout waiting for connection
at org.apache.http.impl.conn.tsccm.ConnPoolByRoute.getEntryBlocking(ConnPoolByRoute.java:417)
at org.apache.http.impl.conn.tsccm.ConnPoolByRoute$1.getPoolEntry(ConnPoolByRoute.java:300)
at org.apache.http.impl.conn.tsccm.ThreadSafeClientConnManager$1.getConnection(ThreadSafeClientConnManager.java:224)
at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:391)
at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:820)
at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:754)
at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:732)

Since both AWS and my requests to the data vendor use Http connections, I am not quite sure where exactly I forget to HttpEntity.consume(), or S3ObjectInputStream.close() (unless it is yet something else…).

So here is my question: are there ways to monitor org.apache.http.impl.conn.tsccm.ConnPoolByRoute so that at least I can detect when I am starting to leak connections/entities not properly consumed/http streams not closed? (I have a feeling it happens only under certain conditions, e.g. when certain exceptions are being thrown, by-passing the logic in my code that consumes HttpEntities, closes streams, etc.) Any idea on how to diagnose what eventually causes all my http connections to fail with that ConnectionPoolTimeoutException would be most welcome. I don’t feel like waiting 4+ days between attempts to fix the root cause of the problem.

Answer 1

If you’re using the PoolingClientConnectionManager note there are the methods getTotalStats() and getStats(final HttpRoute route) which will give you a PoolStats object with the data you’re looking to monitor.

Just fetch the ConnectionManager from your httpclient:

PoolingClientConnectionManager poolManager = (PoolingClientConnectionManager) httpClient.getConnectionManager();