Best Practice to Use HttpClient in Multithreaded Environment

Question

For a while, I have been using HttpClient in a multithreaded environment. For every thread, when it initiates a connection, it will create a completely new HttpClient instance.

Recently, I have discovered that, by using this approach, it can cause the user to have too many ports being opened, and most of the connections are in TIME_WAIT state.

http://www.opensubscriber.com/message/commons-httpclient-dev@jakarta.apache.org/86045.html

Hence, instead of each thread doing :

HttpClient c = new HttpClient();
try {
    c.executeMethod(method);
}
catch(...) {
}
finally {
    method.releaseConnection();
}

We plan to have :

[METHOD A]

// global_c is initialized once through
// HttpClient global_c = new HttpClient(new MultiThreadedHttpConnectionManager());

try {
    global_c.executeMethod(method);
}
catch(...) {
}
finally {
    method.releaseConnection();
}

In a normal situation, global_c will be accessed by 50++ threads concurrently. I was wondering, will this create any performance issues? Is MultiThreadedHttpConnectionManager using a lock-free mechanism to implement its thread safe policy?

If 10 threads are using global_c, will the other 40 threads be locked?

Or would it be better if, in every thread, I create an instance of an HttpClient, but release the connection manager explicitly?

[METHOD B]

MultiThreadedHttpConnectionManager connman = new MultiThreadedHttpConnectionManager();
HttpClient c = new HttpClient(connman);
try {
      c.executeMethod(method);
}
catch(...) {
}
finally {
    method.releaseConnection();
    connman.shutdown();
}

Will connman.shutdown() suffer performance issues?

May I know which method (A or B) is better, for application using an 50++ threads?

Answer 1

Definitely Method A because its pooled and thread safe.

If you are using httpclient 4.x, the connection manager is called ThreadSafeClientConnManager. See this link for further details (scroll down to "Pooling connection manager"). For example:

    HttpParams params = new BasicHttpParams();
    SchemeRegistry registry = new SchemeRegistry();
    registry.register(new Scheme("http", PlainSocketFactory.getSocketFactory(), 80));
    ClientConnectionManager cm = new ThreadSafeClientConnManager(params, registry);
    HttpClient client = new DefaultHttpClient(cm, params);

Answer 2

Method A is recommended by httpclient developer community.

Please refer http://www.mail-archive.com/httpclient-users@hc.apache.org/msg02455.html for more details.

Answer 3

My reading of the docs is that HttpConnection itself is not treated as thread safe, and hence MultiThreadedHttpConnectionManager provides a reusable pool of HttpConnections, you have a single MultiThreadedHttpConnectionManager shared by all threads and initialised exactly once. So you need a couple of small refinements to option A.

MultiThreadedHttpConnectionManager connman = new MultiThreadedHttpConnectionManag

Then each thread should be using the sequence for every request, getting a conection from the pool and putting it back on completion of its work - using a finally block may be good. You should also code for the possibility that the pool has no available connections and process the timeout exception.

HttpConnection connection = null
try {
    connection = connman.getConnectionWithTimeout(
                        HostConfiguration hostConfiguration, long timeout) 
    // work
} catch (/*etc*/) {/*etc*/} finally{
    if ( connection != null )
        connman.releaseConnection(connection);
}

As you are using a pool of connections you won't actually be closing the connections and so this should not hit the TIME_WAIT problem. This approach does assuume that each thread doesn't hang on to the connection for long. Note that conman itself is left open.

Answer 4

I think you will want to use ThreadSafeClientConnManager.

You can see how it works here: http://foo.jasonhudgins.com/2009/08/http-connection-reuse-in-android.html

Or in the AndroidHttpClient which uses it internally.

Answer 5

With HttpClient 4.5 you can do this:

CloseableHttpClient httpClient = HttpClients.custom().setConnectionManager(new PoolingHttpClientConnectionManager()).build();

Note that this one implements Closeable (for shutting down of the connection manager).