In the single-process mode the server receives requests from web clients to a single process. Inside the single server process many threads are running that are waiting for new requests to arrive. When a request arrives, it is handled by the thread receiving the request. Because the server is multi-threaded, all NSAPI extensions written to the server must be thread-safe. This means that if the NSAPI extension uses a global resource, like a shared reference to a file or global variable, then the use of that resource must be synchronized, so that only one thread accesses it at a time. All plugins provided by Netscape/Sun Java System are thread-safe and thread-aware, providing good scalability and concurrency. However, your legacy applications may be single-threaded. When the server runs the application, it can only execute one at a time. This leads to server performance problems when put under load. Unfortunately, in the single-process design, there is no real workaround.