I am in the process of developing an EJB that makes 10+ calls to other components (EJBs, Web services, etc.) as part of it's business logic. In my case, performance is a huge concern. This EJB will be servicing a few million requests a day.
My question is: For each of those 10+ calls, how can I enforce a timeout?
I cannot wait more than 'n' seconds for any one of the calls to return. If a call takes longer than 'n' seconds, I will use a default response for processing.
I would normally use a Executor to solve this problem but, from what I understand, one shouldn't spawn threads from within an EJB as it may potentially interfere with the EJB's lifecycle.
how can I enforce a timeout?
The ejb3.1 specification provides the possibility to set a timeout using #AccessTimeout annotation that applies for serialized client calls that have to wait when an Session Bean instance
is busy executing a previous request.
Clearly (and explicity described in the specification) this applies to StateFul and Singleton session bean, although it could be implemented for Stateless in the case the bean pool run out of available instances.
Notice, once the client-invoked business method is in progress this timeout no applies.
Other possibility that is not part of the specification but, is supported by several servers (see JBoss example) is to define a timeout at the remote client side. If the client invocation
takes longer than the configured timeout, the client will be informed, however, the server execution will not be interrupted which it is not good enough.
Set a transaction timeout neither is a good option because there is no guarantee the thread that executes the business logic will be interrupted when the transaction timeout expires.
I would normally use a Executor to solve this problem but, from what I understand, one shouldn't spawn threads from within an EJB..
Instead you could use ManagedExecutorService class that is an Executor extension suitable to use within a EJB Container.
Aditionally, to implement asynchronous call within an EJB, take a look at #Asynchronous annotation, which provides a high level abstraction to solve the multithreding issue you are facing.
Cancel() method from Future class, allows you to interrup a thread's execution if you consider that the process has taken too long.
since you are not providing much detail of your environment:
use bean managed transactions and set the transaction timeout
EE7: provides an managed executor service
EE6: custom executor service as a JCA connector
Related
I'm struggling with asynchronous processing in Spring. I've decided to use #Acync together with #EnableAsync and ThreadPoolTaskExecutor.
Is there any mechanism responsible for thread's hanging coming together with Spring's #Async? The Async method calls few external resources with RestTemplate and I should probably somehow protect against hanging a thread.
The only possibility of hanging thread with #Async is if request to any external resource goes to hang state due to some network or resource issue.
The solution would be, provide connection timeout for each external resource call.
We are using JTA to manage global transactions in servlet context. Additionally, some of the servlet threads are invoking asynchronous beans. Currently, I have designed it in a way so that the asynchronous bean (Work Manager) gets its own transaction.
It's my understanding that two threads can participate in the same XA transaction. But if I start using the transaction created by the servlet, for the asynchronous bean, will that block the servlet thread until all participant have committed or rolled back? Both the servlet and the async bean can commit and rollback.
The app server is WebSphere, and we are NOT using Spring.
Your response is appreciated.
Using the same transaction both for the servlet thread and an asynchronous worker conflicts somehow with the general idea of messaging. Messaging is a means to decouple, whereas a transaction keeps things tightly together.
In other words, if you want a worker to use the same transaction, I would not implement the worker in an asynchronous way.
As for two threads participating in the same XA transaction, this might not be supported, look here for details. Even if it worked, it could be troublesome to share resources over a thread context generally speaking (file handles, connections, transactions whatever).
As for the servlet thread, whether it blocks: I have never tried it (for the above reasons), but I assume that it does not block: You would have to wait/poll for your async workers, until they have finished (or failed). Otherwise the servlet just reaches your commit statement.
I'm building a plugin that is implemented as a Spring MVC application. This plugin is deployed on 3 - 6 tomcat servers via a gui on one of the servers. Each of the instances of the plugin has an #Scheduled method to collect information on the server and store it in a central database.
My issue is that the gui interface for uninstalling the plugin leaves some of the #Scheduled threads running.
For example, I have an environment that has servers 1 - 3. I install and enable the plugin via the gui on server 1. There are now 3 instances of the application running #Scheduled threads on servers 1 - 3. If I go back to server 1 and uninstall the plugin, the thread is reliably killed on server 1 but not servers 2 or 3.
I've implemented the following but the behavior persists:
#Component
public class ContextClosedListener implements ApplicationListener<ContextClosedEvent> {
#Autowired
ThreadPoolTaskExecutor executor;
#Autowired
ThreadPoolTaskScheduler scheduler;
public void onApplicationEvent(ContextClosedEvent event) {
scheduler.shutdown();
executor.shutdown();
}
}
Additionally, I've thought of implementing this as a context listener rather than an #Scheduled method but I'd rather stick to Spring for maintenance and extensibility reasons.
How can I reliably kill threads in an environment like this?
A couple thoughts I have. ThreadPoolTaskExecutor has a method setThreadNamePrefix, which allows you to set the prefix of the thread. You could set the prefix to something unique, then find and kill those threads at runtime. You can also set the thread group using the setThreadGroup method on the same object, then just stop the threads in the threadgroup.
The better, and safer, solution would be to create a break-out method in your scheduled jobs. This is the prefered method to stopping a Thread instead of the old "shot it in the head" method of calling Thread.stop(). You could get reference to those Runnables either by setting a common prefix or by using the thread group as described above.
The next question is: how do you stop the threads easily? For that, it would depend on how your appliation is implemented. Since I deal mainly with Spring MVC apps, my first solution would be to write a Controller to handle admin tasks. If this was JBoss, or some other large app server that had JMX (Tomcat can be configured to provide JMX I believe, but I don't think its configured out of the box that way), I might write a JMX-enabled bean to allow me to stop the threads via the app servers console. Basically, give your self a method to trigger the stopping of the threads.
When you use javax.xml.ws.Endpoint.publish to handle incoming restful/soap requests, will it generate a thread for each request? or will I have handle threads myself?
I've been trying to work this out for a couple of days now. The documentation hints on threads, but there is nothing specific about this.
Doc says:
An Executor may be set on the endpoint in order to gain better control
over the threads used to dispatch incoming requests. For instance,
thread pooling with certain parameters can be enabled by creating a
ThreadPoolExecutor and registering it with the endpoint.
For me that looks like it handles threads, but you will have no control over them, so adding a ThreadPoolExecutor to execute the threads, you will have a pool of threads you can work with. Is this right?
Examining section 5.2.7 of the JavaTM API for XML-Based Web Services specification (JAX-WS) seems to indicate so, although it looks like there is some room for implementation specific behavior. To really know what is going on you'd have to investigate the JAX-WS implementation you are using and the particular deployment environment. I'd imagine the behavior might be different depending upon whether the service is deployed within a Servlet container or in a standalone process. The control that you do have over the threads is limited to providing a specific ThreadPoolExecutor implementation. Section 5.2.7 states:
5.2.7 Executor
Endpoint instances can be configured with a java.util.concurrent.Executor. The executor will then be used to dispatch any incoming requests to the application. The setExecutor and getExecutor methods of Endpoint can be used to modify and retrieve the executor configured for a service.
<> Conformance (Use of Executor): If an executor object is successfully set on an Endpoint via the setExecutor method, then an implementation MUST use it to dispatch incoming requests upon publication of the Endpoint by means of the publish(String address) method. If publishing is carried out using the publish(Object serverContext)) method, an implementation MAY use the specified executor or another one specific to the server context being used.
<> Conformance (Default Executor): If an executor has not been set on an Endpoint, an implementation MUST use its own executor, a java.util.concurrent.ThreadPoolExecutor or analogous mechanism, to dispatch incoming requests.
Also, section 5.2.2 references 5.2.7 near the end of the section:
5.2.2 Publishing
...
An Endpoint will be typically invoked to serve concurrent requests, so its implementor should be written so as to support multiple threads. The synchronized keyword may be used as usual to control access to critical sections of code. For finer control over the threads used to dispatch incoming requests, an application can directly set the executor to be used, as described in section 5.2.7.
I realize this probably doesn't answer your question exactly, but hopefully it points you in a direction that you can get the answer you are looking for.
An Executor needs to be set in order to make an Endpoint multi-threaded. A simple multi-threaded Executor would be the fixed thread pool Executor.
endpoint.setExecutor(Executors.newFixedThreadPool(4));
This will allow your WebService to accept 4 connections simultaneously. But make sure your Service is thread safe.
I could not find and answer to this in the official doco, but after playing around with it and reading 'Java Web Services: Up and Running', it seems like it does not generate threads for each connections. So the service is blocked until it's done with one request, then a new request is handled.
Endpoint.publish(Url, ServiceImplObj) publishes a webservice at a given url. The no. of threads assigned for request handling truly is under control of the jvm because this is a light weight deployment which is handled by jvm itself.
For better clarification you can print the current thread name at service side and you can see that the service threads are being assigned from a thread pool which is managed by jvm.
[pool-1-thread-1]: Response[57]:
[pool-1-thread-5]: Response[58]:
[pool-1-thread-4]: Response[59]:
[pool-1-thread-3]: Response[60]:
[pool-1-thread-6]: Response[61]:
[pool-1-thread-6]: Response[62]:
I have used jdk1.6.0_35
xjc -version
xjc version "JAXB 2.1.10 in JDK 6"
JavaTM Architecture for XML Binding(JAXB) Reference Implementation, (build JAXB
2.1.10 in JDK 6)
I have a Web application using spring and hibernate and struts (it runs on Tomcat)
The call sequence is something like this...
Struts action calls spring service bean which in turn calls Spring DAO bean. The DAO implementation is a Hibernate implementation.
The question is
Would all my spring beans be running in the same thread ?
Can I store something in the ThreadLocal and get it in another bean?
I am quite sure this would not work in Stateless Session Bean.
The EJB container can (or will) spawn a new thread for every call to the session bean
Will the spring container do the same? i.e. run all beans in the same thread ?
When I tried a JUnit test - I got the same id via Thread.currentThread().getId() in the Test Case and the two beans- which leads me to believe there was only one thread in action
Or is the behavior unpredictable?
Or will it change when running on Tomcat server ?
Clarification
I do not wish to exchange data between two threads. I want to put data in the ThreadLocal and be able to retrieve it from all beans in the call stack. This will work only if all beans are in the same thread
Spring doesn't spawn the threads. Tomcat does. Spring is just creating and wiring up the objects for you.
Each request from the browser is processed in one request. It is Tomcat that handles the request. It is Tomcat that creates the thread to process the request.
Assuming you have just created a singleton bean in Spring called "X". Then the same instance of X is used by all requests.
The Spring beans don't live in a thread. They are just allocated on the heap.
Would all my spring beans be running
in the same thread ? Can I store
something in the ThreadLocal and get
it in another bean?
AFAIK for the components you mentioned (service bean, DAO bean - i guess they are plain spring beans), Spring does not spawn a new thread. I do not understand your use case (ie, exchanging data between two threads).
For most webapps, a new thread is spawned for each new request, and if you want to share data between two requests you normally:
- use the get/post parameters to pass the data
- use the session to share data
To answer your question, I'm pretty sure the spring container does not spawn threads for most components.
Yes, you can do this. The same thread will be used to execute your action so the ThreadLocal will work. Typically, the same thread is used for the stateless session bean as well, assuming it is running in the same app server instance. I would not depend on this though, as it is probably vendor dependent.
We use this technique to access the callers identity anywhere in the code. We use session beans and jms as well, but explicitly pass the information between containers and set the ThreadLocal at each entry point. This way it doesn't matter if the bean (session or mdb) are local or not.
In addition to all the other answers, I will just add the following:
Normally the only reason to switch threads is because of some requirement for parallellity. Since this normally does not come for free in terms of complexity, you will usually be clearly informed when this happens.
Switching threads within what appears to be a single-threaded processing of a request is actually extremely complex. This will normally only happen at one place in a container, and this is usually handled by tcp/ip socket readers that receive the request from the external clients. These reader threads usually determine which thread(pool) should process the request and forward the request to that thread. After that the request stays with that thread.
So normally the only thing that will/can happen is that additional threads get created for parallelity or asynchronous processing (like JMS).