I was wondering, whether is AndroidHttpClient thread safe, as this is not being mentioned in documentation. Means, a single instance of AndroidHttpClient can be shared among multiple threads.
Yes, it is thread safe.
AndroidHttpClient is a special implementation of DefaultHttpClient which is pre-configured for Android. It registers the ThreadSafeClientConnManager which allows thread safe HTTP access via a managed connection pool. AndroidHttpClient also applies reasonable default settings for timeouts and socket buffer sizes. It also supports HTTPS by default.
You can find the source code here.