On Thu, 2012-12-13 at 22:18 +0200, Marko Asplund wrote:
> Hi,
>
> I'm having problems using HttpClient in a multi-threaded environment.
> When HttpClient.execute is called I occasionally get the following
> error, even when there
> probably should be connections available in the pool.
>
This can happen if you have a pool with the number of concurrent
connections much smaller than the number of work threads (which causes a
high resource contention) combined with an aggressive timeout value.
> org.apache.http.conn.ConnectionPoolTimeoutException: Timeout waiting
> for connection from pool
> at
> org.apache.http.impl.conn.PoolingClientConnectionManager.leaseConnection(PoolingClientConnectionManager.java:232)
> [httpclient-4.2.2.jar:4.2.2]
> at
> org.apache.http.impl.conn.PoolingClientConnectionManager$1.getConnection(PoolingClientConnectionManager.java:199)
> [httpclient-4.2.2.jar:4.2.2]
> at
> org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:455)
> [httpclient-4.2.2.jar:4.2.2]
> at
> org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:906)
> [httpclient-4.2.2.jar:4.2.2]
> at
> org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:805)
> [httpclient-4.2.2.jar:4.2.2]
> at
> org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:784)
> [httpclient-4.2.2.jar:4.2.2]
> ...
>
> Should I explicitly release the connection after each HTTP request is
> executed?
> Is there something else that should be done to clean up after each request?
> The HC tutorial recommends passing a per-thread HttpContext object to
> HC.execute but is this required?
> What kind of state is actually stored in HttpContext?
>
> Below is a simplified version of the code.
>
> // one-time initialization
> PoolingClientConnectionManager cm = new PoolingClientConnectionManager();
> cm.setDefaultMaxPerRoute(20);
> HttpClient httpClient = new DefaultHttpClient(cm);
>
> // executed repeatedly by multiple concurrent threads
> HttpGet rq = new HttpGet(uri);
> InputStream is = null;
> try {
> HttpResponse res = httpClient.execute(rq);
> // ...
> is = res.getEntity().getContent();
> } finally {
> is.close();
> }
>
Closing the response content stream is perfectly sufficient. Just make
sure your code _always_ consumes response entities even for non-200
responses.
Hope this helps
Oleg
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