Singlethreadmodel interface

Singlethreadmodel interface

This interface is currently deprecated since Servlet API because it doesn't solves all the thread-safety issues such as static variable and session attributes can be accessed by multiple threads at the same time even if we have implemented the SingleThreadModel interface  · The servlet programmer should implement SingleThreadModel interface to ensure that servlet can handle only one request at a time. It is a marker interface, means have no methods. This interface is currently deprecated since Servlet API because it doesn't solves all the thread-safety issues such as static variable and session attributes can be accessed by Example of SingleThreadModel interface. The servlet programmer should implement SingleThreadModel interface to ensure that servlet can handle only one request at a time. It is a marker interface, means have no methods. This interface is currently deprecated since Servlet API because it doesn't solves all the thread-safety issues such as static

SingleThreadModel interface – Code Bridge Plus

Normally, the system makes a single instance of your servlet and then creates a new thread for each user request. This means that if a new request comes in while a previous request is still executing, multiple threads can concurrently be accessing the same servlet object.

Consequently, singlethreadmodel interface, your doGet and doPost methods must be careful to synchronize access to fields and other shared data if any since multiple threads may access the data simultaneously. Note that local variables are not shared by multiple threads, and thus need no special protection.

In principle, you can prevent multithreaded access by having your servlet implement the SingleThreadModel interface, singlethreadmodel interface, as below. If you implement this interface, singlethreadmodel interface, the system guarantees that there is never more than one request thread accessing a single instance of your servlet. In most cases, it does so by queuing all singlethreadmodel interface requests and passing them one at a time to a single servlet instance.

However, the server is permitted to create a pool of multiple instances, each of which handles one request at a time. Either way, this means that you don't have to worry about simultaneous access to regular fields instance variables of the servlet. You dohowever, singlethreadmodel interface, still have to synchronize access to class variables static fields or shared data stored outside the servlet. Although SingleThreadModel prevents concurrent access in principle, in practice there are two reasons why it is usually a poor choice.

First, synchronous access to your servlets can significantly hurt performance latency if your servlet is accessed frequently. So, think twice before using the SingleThreadModel approach. Instead, consider synchronizing only the part of the code that manipulates the shared data. The second problem with SingleThreadModel stems from the fact that the specification permits servers to use pools of instances instead of queueing up the requests to a single instance.

As long as each instance handles only one request at a time, the pool-of-instances approach satisfies the requirements of the specification. But, it is a singlethreadmodel interface idea. Suppose, on one hand, that you are using regular non-static instance variables fields to refer to shared data, singlethreadmodel interface.

Sure, SingleThreadModel prevents concurrent access, singlethreadmodel interface, but it does so by throwing out the baby with the bath water: each servlet instance has a separate copy of the instance variables, so the data is no longer shared properly.

On the other hand, suppose that you are using static instance variables to refer to the shared data. In that case, the pool-of-instances approach to SingleThreadModel provides no advantage whatsoever; multiple requests using different instances can still concurrently access the static data, singlethreadmodel interface. Now, SingleThreadModel is still occasionally useful. For example, it can be used when the singlethreadmodel interface variables are reinitialized for each request singlethreadmodel interface. But, the problems with SingleThreadModel are so severe that it is deprecated in the singlethreadmodel interface 2.

You are much better off using explicit synchronized blocks. Avoid implementing SingleThreadModel for high-traffic servlets. Use it with great caution at other times. For production-level code, explicit code synchronization is almost always better. SingleThreadModel is deprecated in version 2. For example, consider the singlethreadmodel interface of Listing 3. It uses an instance variable field called nextID to keep track of which ID should be assigned nextsinglethreadmodel interface, and uses the following code to output the ID.

Now, suppose you were very careful in testing this servlet. You started the server. Every time you accessed it, you got a different value Figure So the code is correct, singlethreadmodel interface The problem occurs only when there are multiple simultaneous accesses to the servlet. Even then, it occurs only once in a while. But, in a few cases, the first client could read the nextID field and have its thread preempted before it incremented the field.

Then, a second client could read the field and get the same value as the first client. Big trouble! For example, there have been real-world e-commerce applications where customer purchases were occasionally charged to the wrong client's credit card, precisely because of such a race condition in the generation of user IDs.

Now, if you are familiar with multithreaded programming, the problem was very obvious to you. The question is, what is the proper solution? Here are three possibilities. Shorten the race. Remove the third line of the code snippet and change the first line to the following. This approach decreases the likelihood of an incorrect answer, but does not eliminate the possibility.

In many scenarios, lowering the probability of a wrong answer is a bad thing, not a good thing: it merely singlethreadmodel interface that the problem is less likely to be detected in testing, and more likely to occur after being fielded. Use SingleThreadModel. Change the servlet class definition to the following. Will this work? If the server implements SingleThreadModel by queueing up all the requests, then, yes, this will work, singlethreadmodel interface.

But at a performance cost if there is a lot of concurrent access. Even worseif the server implements SingleThreadModel by making a pool of servlet instances, this approach will totally fail because each instance will have its own nextID field.

Either server implementation approach is legal, so this "solution" is no solution at all. Synchronize the code explicitly. Use the standard synchronization singlethreadmodel interface of the Java programming language. Start a synchronized block just before the first access to the shared data, and end the block just after the last update to the data, as follows. This technique tells the system that, once a thread has entered the above block of code or any other synchronized section labelled with the same object referenceno other thread is allowed in until the first thread exits.

This is the solution you have always used in the Java programming language, singlethreadmodel interface. It is the right one here, too. Forget error-prone and low-performance SingleThreadModel shortcuts; fix race conditions the right way. Previous page. Singlethreadmodel interface of content. Next page. public class YourServlet extends HttpServlet implements SingleThreadModel { Core Warning Avoid implementing SingleThreadModel for high-traffic servlets.

Core Servlets and Javaserver Pages: Core Technologies, Vol. Authors: Marty HallLarry Brown. BUY ON AMAZON, singlethreadmodel interface.

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SingleThreadModel (Java(TM) EE 7 Specification APIs)

Now, SingleThreadModel is still occasionally useful. For example, it can be used when the instance variables are reinitialized for each request (e.g., when they are used merely to simplify communication among methods). But, the problems with SingleThreadModel are so severe that it is deprecated in the servlet (JSP ) specification This interface is currently deprecated since Servlet API because it doesn't solves all the thread-safety issues such as static variable and session attributes can be accessed by multiple threads at the same time even if we have implemented the SingleThreadModel interface Example of SingleThreadModel interface. The servlet programmer should implement SingleThreadModel interface to ensure that servlet can handle only one request at a time. It is a marker interface, means have no methods. This interface is currently deprecated since Servlet API because it doesn't solves all the thread-safety issues such as static