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From Oleg Kalnichevski <ol...@apache.org>
Subject Re: ClientMultiThreaded Example
Date Sun, 06 Apr 2008 10:58:27 GMT

On Fri, 2008-04-04 at 14:35 +0000, John Baxter wrote:
> Hi Folks,  
>     Im hope some one can shed some light on this for me. Im currently doing a prototype
and decided i would do it with the httpclient4.0 alpha3 version. I have or will have a multi-threaded
scenario so i have a very similar set up as the ClientMultiThreadedExecution example located
here
> http://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk/module-client/src/examples/org/apache/http/examples/client/ClientMultiThreadedExecution.java
> 
> Anyways i have the use case that should my server go down, my app will wait till it comes
back up. So i have a worker thread that polls the server or tries to poll the server every
30 seconds. Now i re-use the same httpclient instance right throughout the whole application
> 
> Now what i see in the log file is as follows
> 18203 [Thread-1] DEBUG org.apache.http.impl.client.ClientParamsStack  - 'http.protocol.max-redirects':
null
> 18203 [Thread-1] DEBUG org.apache.http.impl.client.ClientParamsStack  - 'http.connection-manager.timeout':
null
> 18203 [Thread-1] DEBUG org.apache.http.impl.conn.tsccm.ThreadSafeClientConnManager  -
ThreadSafeClientConnManager.getConnection: HttpRoute[{}->http://localhost:8080], timeout
= 0
> 18203 [Thread-1] DEBUG org.apache.http.impl.conn.tsccm.ConnPoolByRoute  - No free connections.
HttpRoute[{}->http://localhost:8080]

The connection manager blocks because it has run of free connections.
Apparently your application is leaking connections.

> 18203 [Thread-1] DEBUG org.apache.http.impl.conn.tsccm.ConnPoolByRoute  - Need to wait
for connection. HttpRoute[{}->http://localhost:8080]
> 
> My problem is that the client just hangs and i think it is due to the "Need to wait for
connection" part.  
> 
> 18203 [Thread-1] DEBUG org.apache.http.impl.conn.tsccm.ConnPoolByRoute  - Need to wait
for connection. HttpRoute[{}->http://localhost:8080]
> How long does a thread wait until it gets a free connection?? infinity?

It will block infinitely because the connection manager timeout value is
set to zero. 

ThreadSafeClientConnManager.getConnection:
HttpRoute[{}->http://localhost:8080], timeout = 0


> ? Or how is it released?? My polling thread is just hanging. I restart the server but
the polling thread is still waiting/hanging.
> 
> I have taken the same scenario and used the http client 3.1 and have no problems like
above.
> 
> I think i read somewhere that the connection is returned back to the pool when the input
stream is closed. Now if the server is down, i dont get a response input stream, so does the
httpget.abort release the connection back to the pool? 

Yes, it does.


> I dont think it has anything to do with the TIME_WAIT state either, once the thread enters
the "need to wait for connection" it will hang for infinity. I tried to get a hold of the
current threads connection but the API doesnt give me that chance, just so i could close the
connection myself and not be dependant on whats underneath to clean up.
> 
> Anybody any input as to why my polling thread just hangs in a wait state for infinity??

Because of a connection leak somewhere. It can be either in your code or
in Httpclient itself. Please upgrade to the latest SVN snapshot and
re-test. If the problem persists, let me know.

Oleg 
> 
> Cheers,
> JB
> 
> 
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