amitabh mehra

Marc Cracco wrote:Might sound like a beginner question but why shouldn't you access a static variable from a local synchronized method?

Sorry if my previous post confused you. You are right, static variables can be accessed in local synchronized methods. But the lock should be on the Class again or some other static lock object. That is what i wanted to say in my previous post; but framed the sentence poorly

To access static variables from methods, those methods should be static. In that case, you need to synchronize on the Class.

I had already done that Ajay but i was looking for some application level code snippet / example to implement this

This is a problem of DB transactional concurrency control. It could be solved efficiently using optimistic concurrency control (by maintaining a version_id column in the DB table for Seats).

Ajay, can you please elaborate on this approach?

Thanks... that cleared my doubts!

Thread.State[] ts = e.values();

would return you an array of enum of Thread.State, and you are printing the same. These are not your "current thread" states.
Please check http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Thread.State.htmlfor more info.

I am not able to understand the difference between the two. In case if I use an ArrayList of Future to store the Future returned to me by submitting the tasks through ExecutorService, is it not same as CompletionService implementation?

Also, I need help to identify why the following code does not exit after rendering the page.
Code description: To render a page, there are 2 main tasks: render text and render image (in code, 5 in numbers). For test purpose, I was creating Image data as simple print statement. Each image consists of random number (max of 5) of such statements.

import java.util.concurrent.*; import java.util.*; import java.util.Random; class ImageData { private StringBuffer st; public ImageData(String image) { st = new StringBuffer(image); createImageData(); } private void createImageData() { Random r = new Random(); int i = r.nextInt(8); for (int k = 0; k < i; k++) { st.append("\nImage Data " ).append(k); } } public void printImage() { System.out.println(st); } } class ImageInfo { private ImageData id; private String image; public ImageInfo(int i ) { image = "Image " + i; id = new ImageData(image); } public ImageData downloadInfo() { return id; } } class Renderer { public final ExecutorService execService; public final List<Future<ImageData>> list = new ArrayList<Future<ImageData>>(); public Renderer(ExecutorService exec) { execService = exec; } void renderPage() { System.out.println ("*********** Render Page **************"); final List<ImageInfo> info = scanForImage(); for(final ImageInfo im : info) { Callable<ImageData> task = new Callable<ImageData>() { public ImageData call() { return im.downloadInfo(); } }; list.add(execService.submit(task)); } renderText(); try { for(Future<ImageData> f : list) { ImageData id = f.get(); renderImage(id); } } catch(InterruptedException ie) { ie.printStackTrace(); } catch(ExecutionException ie) { ie.printStackTrace(); } System.out.println("Page Rendered"); } List<ImageInfo> scanForImage() { List<ImageInfo> l = new ArrayList<ImageInfo>(); for(int i = 0 ; i < 5; i++) { ImageInfo im = new ImageInfo(i); l.add(im); } return l; } void renderText() { System.out.println("************ Render Text *****************"); Random r = new Random(); try { Thread.currentThread().sleep(r.nextInt(5) * 1000); } catch(InterruptedException ie) { ie.printStackTrace(); } System.out.println("Text Rendered"); } void renderImage(ImageData id) { System.out.println("************ Render Image*****************"); Random r = new Random(); try { Thread.currentThread().sleep(r.nextInt(5) * 1000); } catch(InterruptedException ie) { ie.printStackTrace(); } id.printImage(); } } public class Test { public static void main(String[] args) { ExecutorService e = Executors.newFixedThreadPool(3); Renderer r = new Renderer(e) ; r.renderPage(); System.out.println("Done"); } }

1) notify() does not guarantee that consumer thread will be the next thread to run. It only guarantees that consumer thread is now *eligible to run*, but, since now both threads - Producer thread and Consumer thread are *eligible to run*, it all depends on the Thread Scheduler to schedule which thread should go next.

2) Consumer thread is not consuming in chaotic manner.

System.out.println(t.getName() + " consumed: " + prod.i);

You are printing the prod.i value. This will be the most recent one.

Better option to implement a Producer/Consumer problem would be to go for BlockingQueues else have some shared DataStructure in which Producer can go on inserting and consumer can pick items from there.

Ankur Jain Kothari wrote:ok...but what if i want to enter 1 first...then computer asking me to type the second number and then i type 2 and then Enter.? Can this be possible? how can we do this with getchar? here with getchar, it reads the first charachter and then 2nd charachter upon being called again...?

i hope my question is clear

any specific reason that you want only getchar()? you can very well use scanf or fscanf to get user input, one at a time, and parse them in whatever way you want or validate them before using them.

not directly.. but in implementation I think that this could be achieved... just an idea..
Use one lockObject ( create a class with some private member which will hold the next thread's name .. usual getter and setter methods)
Before starting all threads, set this member value to a given thread name, say "Thread 2"

In the run method, we will check if the current thread name is "Thread 2" then let it continue with its work else make it wait.
After completing its work, Thread 2 would set the member to next thread name... and then notify all.

Henry, can you elaborate how is that a spin wait. If i use thread.yield() will the thread not yield the cpu to other threads.
coming on top of this is another question which i m not sure is valid or not, still here it is - will yield() method, yield cpu to same and higher priority threads or any thread?

Okies Jaikiran, let me try in this forum also

i have already given the servlet mapping in my earlier post.
any help will be highly appreciated

Jaikiran

I can access the url http://localhost:8080/MyStore/MyStore/userRegister.html
on submitting the form, it should call a servlet... as I have already stated in my earlier post, but it fails giving 404.

it surely has to do something with the paths... ahhhhhhh.. this is so irritating dont know how to proceed....

@Jaikiran
did you get any clue from the log?

any help in this will be highly appreciated because i am stuck at this point and atmost i can do now is just read but cant implement and test...

sorry to update the thread so late... was not able to try the suggestions.

@Satya
tried after changing the application.xml.... nope, it didnt work.

@Jaikiran
Here is the console prints while bringing up the jboss server... might be too big... but was not sure what to leave out
(tried attaching it as txt / log file.. not allowed to upload)


18:06:07,984 INFO [ConnectionFactoryBindingService] Bound ConnectionManager 'jboss.jca:service=ConnectionFacto ryBinding,name=JmsXA' to JNDI name 'java:JmsXA' 18:06:08,453 INFO [ConnectionFactoryBindingService] Bound ConnectionManager 'jboss.jca:service=DataSourceBindi ng,name=myStoreDS' to JNDI name 'java:myStoreDS' 18:06:08,812 INFO [TomcatDeployment] deploy, ctxPath=/ 18:06:12,515 INFO [TomcatDeployment] deploy, ctxPath=/jmx-console 18:06:15,187 INFO [JBossASKernel] Created KernelDeployment for: myStore-ejb.jar 18:06:15,218 INFO [JBossASKernel] installing bean: jboss.j2ee:ear=myStore.ear,jar=myStore-ejb.jar,name=BillMan agerBean,service=EJB3 18:06:15,218 INFO [JBossASKernel] with dependencies: 18:06:15,218 INFO [JBossASKernel] and demands: 18:06:15,218 INFO [JBossASKernel] jboss.ejb:service=EJBTimerService 18:06:15,218 INFO [JBossASKernel] persistence.unit:unitName=myStore.ear/myStore-ejb.jar#myStore 18:06:15,218 INFO [JBossASKernel] and supplies: 18:06:15,218 INFO [JBossASKernel] jndi:myStore/BillManagerBean/remote 18:06:15,218 INFO [JBossASKernel] jndi:myStore/BillManagerBean/remote-com.myStore.models.BillManager 18:06:15,218 INFO [JBossASKernel] Class:com.myStore.models.BillManager 18:06:15,218 INFO [JBossASKernel] Added bean(jboss.j2ee:ear=myStore.ear,jar=myStore-ejb.jar,name=BillManagerBe an,service=EJB3) to KernelDeployment of: myStore-ejb.jar 18:06:15,218 INFO [JBossASKernel] installing bean: jboss.j2ee:ear=myStore.ear,jar=myStore-ejb.jar,name=Categor yManagerBean,service=EJB3 18:06:15,218 INFO [JBossASKernel] with dependencies: 18:06:15,218 INFO [JBossASKernel] and demands: 18:06:15,218 INFO [JBossASKernel] jboss.ejb:service=EJBTimerService 18:06:15,218 INFO [JBossASKernel] persistence.unit:unitName=myStore.ear/myStore-ejb.jar#myStore 18:06:15,218 INFO [JBossASKernel] and supplies: 18:06:15,218 INFO [JBossASKernel] jndi:myStore/CategoryManagerBean/remote-com.myStore.models.CategoryMana ger 18:06:15,218 INFO [JBossASKernel] jndi:myStore/CategoryManagerBean/remote 18:06:15,218 INFO [JBossASKernel] Class:com.myStore.models.CategoryManager 18:06:15,218 INFO [JBossASKernel] Added bean(jboss.j2ee:ear=myStore.ear,jar=myStore-ejb.jar,name=CategoryManag erBean,service=EJB3) to KernelDeployment of: myStore-ejb.jar 18:06:15,234 INFO [JBossASKernel] installing bean: jboss.j2ee:ear=myStore.ear,jar=myStore-ejb.jar,name=ItemMan agerBean,service=EJB3 18:06:15,234 INFO [JBossASKernel] with dependencies: 18:06:15,234 INFO [JBossASKernel] and demands: 18:06:15,234 INFO [JBossASKernel] jboss.ejb:service=EJBTimerService 18:06:15,234 INFO [JBossASKernel] persistence.unit:unitName=myStore.ear/myStore-ejb.jar#myStore 18:06:15,234 INFO [JBossASKernel] and supplies: 18:06:15,234 INFO [JBossASKernel] Class:com.myStore.models.ItemManager 18:06:15,234 INFO [JBossASKernel] jndi:myStore/ItemManagerBean/remote 18:06:15,234 INFO [JBossASKernel] jndi:myStore/ItemManagerBean/remote-com.myStore.models.ItemManager 18:06:15,234 INFO [JBossASKernel] Added bean(jboss.j2ee:ear=myStore.ear,jar=myStore-ejb.jar,name=ItemManagerBe an,service=EJB3) to KernelDeployment of: myStore-ejb.jar 18:06:15,234 INFO [JBossASKernel] installing bean: jboss.j2ee:ear=myStore.ear,jar=myStore-ejb.jar,name=UserMan agerBean,service=EJB3 18:06:15,234 INFO [JBossASKernel] with dependencies: 18:06:15,234 INFO [JBossASKernel] and demands: 18:06:15,234 INFO [JBossASKernel] jboss.ejb:service=EJBTimerService 18:06:15,234 INFO [JBossASKernel] persistence.unit:unitName=myStore.ear/myStore-ejb.jar#myStore 18:06:15,234 INFO [JBossASKernel] and supplies: 18:06:15,234 INFO [JBossASKernel] Class:com.myStore.models.UserManager 18:06:15,234 INFO [JBossASKernel] jndi:myStore/UserManagerBean/remote-com.myStore.models.UserManager 18:06:15,234 INFO [JBossASKernel] jndi:myStore/UserManagerBean/remote 18:06:15,234 INFO [JBossASKernel] Added bean(jboss.j2ee:ear=myStore.ear,jar=myStore-ejb.jar,name=UserManagerBe an,service=EJB3) to KernelDeployment of: myStore-ejb.jar 18:06:15,734 INFO [PersistenceUnitDeployment] Starting persistence unit persistence.unit:unitName=myStore.ear/ myStore-ejb.jar#myStore 18:06:16,109 INFO [Version] Hibernate Annotations 3.4.0.GA 18:06:16,500 INFO [Environment] Hibernate 3.3.1.GA 18:06:16,593 INFO [Environment] hibernate.properties not found 18:06:16,593 INFO [Environment] Bytecode provider name : javassist 18:06:16,640 INFO [Environment] using JDK 1.4 java.sql.Timestamp handling 18:06:19,796 INFO [Version] Hibernate Commons Annotations 3.1.0.GA 18:06:19,890 INFO [Version] Hibernate EntityManager 3.4.0.GA 18:06:20,234 WARN [Ejb3Configuration] Persistence provider caller does not implement the EJB3 spec correctly. PersistenceUnitInfo.getNewTempClassLoader() is null. 18:06:20,703 INFO [AnnotationBinder] Binding entity from annotated class: com.myStore.models.Item 18:06:21,046 INFO [EntityBinder] Bind entity com.myStore.models.Item on table Item 18:06:21,796 INFO [AnnotationBinder] Binding entity from annotated class: com.myStore.models.User 18:06:21,796 INFO [EntityBinder] Bind entity com.myStore.models.User on table USER 18:06:21,828 INFO [AnnotationBinder] Binding entity from annotated class: com.myStore.models.Bill 18:06:21,828 INFO [EntityBinder] Bind entity com.myStore.models.Bill on table bill 18:06:21,843 INFO [AnnotationBinder] Binding entity from annotated class: com.myStore.models.Category 18:06:21,843 INFO [EntityBinder] Bind entity com.myStore.models.Category on table category 18:06:23,093 INFO [CollectionBinder] Mapping collection: com.myStore.models.User.bills -> bill 18:06:23,093 INFO [CollectionBinder] Mapping collection: com.myStore.models.User.items -> Item 18:06:23,093 INFO [CollectionBinder] Mapping collection: com.myStore.models.Bill.items -> Item 18:06:23,156 INFO [Version] Hibernate Validator 3.1.0.GA 18:06:23,437 INFO [HibernateSearchEventListenerRegister] Unable to find org.hibernate.search.event.FullTextInd exEventListener on the classpath. Hibernate Search is not enabled. 18:06:23,859 INFO [ConnectionProviderFactory] Initializing connection provider: org.hibernate.ejb.connection.I njectedDataSourceConnectionProvider 18:06:23,875 INFO [InjectedDataSourceConnectionProvider] Using provided datasource 18:06:27,218 INFO [SettingsFactory] RDBMS: MySQL, version: 5.0.18 18:06:27,218 INFO [SettingsFactory] JDBC driver: MySQL-AB JDBC Driver, version: mysql-connector-java-5.0.8 ( R evision: ${svn.Revision} ) 18:06:27,390 INFO [Dialect] Using dialect: org.hibernate.dialect.MySQLInnoDBDialect 18:06:27,406 INFO [TransactionFactoryFactory] Transaction strategy: org.hibernate.ejb.transaction.JoinableCMTT ransactionFactory 18:06:27,421 INFO [TransactionManagerLookupFactory] instantiating TransactionManagerLookup: org.hibernate.tran saction.JBossTransactionManagerLookup 18:06:27,453 INFO [TransactionManagerLookupFactory] instantiated TransactionManagerLookup 18:06:27,453 INFO [SettingsFactory] Automatic flush during beforeCompletion(): disabled 18:06:27,453 INFO [SettingsFactory] Automatic session close at end of transaction: disabled 18:06:27,468 INFO [SettingsFactory] JDBC batch size: 15 18:06:27,468 INFO [SettingsFactory] JDBC batch updates for versioned data: disabled 18:06:27,484 INFO [SettingsFactory] Scrollable result sets: enabled 18:06:27,484 INFO [SettingsFactory] JDBC3 getGeneratedKeys(): enabled 18:06:27,484 INFO [SettingsFactory] Connection release mode: auto 18:06:27,500 INFO [SettingsFactory] Maximum outer join fetch depth: 2 18:06:27,500 INFO [SettingsFactory] Default batch fetch size: 1 18:06:27,500 INFO [SettingsFactory] Generate SQL with comments: disabled 18:06:27,500 INFO [SettingsFactory] Order SQL updates by primary key: disabled 18:06:27,531 INFO [SettingsFactory] Order SQL inserts for batching: disabled 18:06:27,531 INFO [SettingsFactory] Query translator: org.hibernate.hql.ast.ASTQueryTranslatorFactory 18:06:27,890 INFO [ASTQueryTranslatorFactory] Using ASTQueryTranslatorFactory 18:06:27,890 INFO [SettingsFactory] Query language substitutions: {} 18:06:27,890 INFO [SettingsFactory] JPA-QL strict compliance: enabled 18:06:27,890 INFO [SettingsFactory] Second-level cache: enabled 18:06:27,890 INFO [SettingsFactory] Query cache: disabled 18:06:28,000 INFO [SettingsFactory] Cache region factory : org.hibernate.cache.impl.bridge.RegionFactoryCacheP roviderBridge 18:06:28,015 INFO [RegionFactoryCacheProviderBridge] Cache provider: org.hibernate.cache.HashtableCacheProvide r 18:06:28,015 INFO [SettingsFactory] Optimize cache for minimal puts: disabled 18:06:28,015 INFO [SettingsFactory] Cache region prefix: persistence.unit:unitName=myStore.ear/myStore-ejb.jar #myStore 18:06:28,015 INFO [SettingsFactory] Structured second-level cache entries: disabled 18:06:28,125 INFO [SettingsFactory] Statistics: disabled 18:06:28,125 INFO [SettingsFactory] Deleted entity synthetic identifier rollback: disabled 18:06:28,125 INFO [SettingsFactory] Default entity-mode: pojo 18:06:28,125 INFO [SettingsFactory] Named query checking : enabled 18:06:28,921 INFO [SessionFactoryImpl] building session factory 18:06:35,234 INFO [SessionFactoryObjectFactory] Factory name: persistence.unit:unitName=myStore.ear/myStore-ej b.jar#myStore 18:06:35,328 INFO [NamingHelper] JNDI InitialContext properties:{java.naming.factory.initial=org.jnp.interface s.NamingContextFactory, java.naming.factory.url.pkgs=org.jboss.naming:org.jnp.interfaces} 18:06:35,718 INFO [NamingHelper] Creating subcontext: persistence.unit:unitName=myStore.ear 18:06:35,718 INFO [SessionFactoryObjectFactory] Bound factory to JNDI name: persistence.unit:unitName=myStore. ear/myStore-ejb.jar#myStore 18:06:35,718 WARN [SessionFactoryObjectFactory] InitialContext did not implement EventContext 18:06:36,031 INFO [SchemaExport] Running hbm2ddl schema export 18:06:36,046 INFO [SchemaExport] exporting generated schema to database 18:06:45,156 INFO [SchemaExport] schema export complete 18:06:45,187 INFO [NamingHelper] JNDI InitialContext properties:{java.naming.factory.initial=org.jnp.interface s.NamingContextFactory, java.naming.factory.url.pkgs=org.jboss.naming:org.jnp.interfaces} 18:06:47,734 INFO [SessionSpecContainer] Starting jboss.j2ee:ear=myStore.ear,jar=myStore-ejb.jar,name=BillMana gerBean,service=EJB3 18:06:48,562 INFO [EJBContainer] STARTED EJB: com.myStore.models.BillManagerBean ejbName: BillManagerBean 18:06:49,656 INFO [SessionSpecContainer] Starting jboss.j2ee:ear=myStore.ear,jar=myStore-ejb.jar,name=UserMana gerBean,service=EJB3 18:06:49,656 INFO [EJBContainer] STARTED EJB: com.myStore.models.UserManagerBean ejbName: UserManagerBean 18:06:49,671 INFO [SessionSpecContainer] Starting jboss.j2ee:ear=myStore.ear,jar=myStore-ejb.jar,name=ItemMana gerBean,service=EJB3 18:06:49,671 INFO [EJBContainer] STARTED EJB: com.myStore.models.ItemManagerBean ejbName: ItemManagerBean 18:06:49,718 INFO [SessionSpecContainer] Starting jboss.j2ee:ear=myStore.ear,jar=myStore-ejb.jar,name=Category ManagerBean,service=EJB3 18:06:49,734 INFO [EJBContainer] STARTED EJB: com.myStore.models.CategoryManagerBean ejbName: CategoryManagerB ean 18:06:50,187 INFO [JndiSessionRegistrarBase] Binding the following Entries in Global JNDI: myStore/CategoryManagerBean/remote - EJB3.x Default Remote Business Interface myStore/CategoryManagerBean/remote-com.myStore.models.CategoryManager - EJB3.x Remote Business Interfac e 18:06:51,828 INFO [JndiSessionRegistrarBase] Binding the following Entries in Global JNDI: myStore/ItemManagerBean/remote - EJB3.x Default Remote Business Interface myStore/ItemManagerBean/remote-com.myStore.models.ItemManager - EJB3.x Remote Business Interface 18:06:51,859 INFO [JndiSessionRegistrarBase] Binding the following Entries in Global JNDI: myStore/UserManagerBean/remote - EJB3.x Default Remote Business Interface myStore/UserManagerBean/remote-com.myStore.models.UserManager - EJB3.x Remote Business Interface 18:06:51,890 INFO [JndiSessionRegistrarBase] Binding the following Entries in Global JNDI: myStore/BillManagerBean/remote - EJB3.x Default Remote Business Interface myStore/BillManagerBean/remote-com.myStore.models.BillManager - EJB3.x Remote Business Interface 18:07:01,484 INFO [TomcatDeployment] deploy, ctxPath=/MyStore 18:07:02,515 WARN [config] Unable to process deployment descriptor for context '/MyStore' 18:07:06,859 INFO [Http11Protocol] Starting Coyote HTTP/1.1 on http-127.0.0.1-8080 18:07:07,000 INFO [AjpProtocol] Starting Coyote AJP/1.3 on ajp-127.0.0.1-8009 18:07:07,031 INFO [ServerImpl] JBoss (Microcontainer) [5.0.1.GA (build: SVNTag=JBoss_5_0_1_GA date=20090223204 8)] Started in 3m:8s:16ms


I hope it will help to get where I am going wrong.