Re: Can servlets safely spawn threads?
Many thanks! On 29/01/07, Bill Au <[EMAIL PROTECTED]> wrote: If you are spawning threads from your servlet, make sure that they are cleaned up when the servlet is destroyed. Otherwise, you will have a thread leak. I have ran into this problem when the webapp is reloaded without restarting the server. Each leaked thread has a reference to its classloader, preventing that classloader from being garbage collected. Reload enough time will run the perm space out of memory. Bill On 1/29/07, Christopher Schultz <[EMAIL PROTECTED]> wrote: > > -BEGIN PGP SIGNED MESSAGE- > Hash: SHA1 > > Danny, > > David Delbecq wrote: > > 1) Your servlet must always take care to finish all Threads it has > > spawned. This mean when servlet gets unloaded, you must have provided a > > mecanism in your servlet to stop all running threads your servlet has > > created. Remaining Threads not handled by container can either cause > > tomcat to not stop when requested or prevent garbage collecting of > > webapp when reloading. > > Consider using an existing thread pool component. It should have a > graceful shutdown capability already built into it. David is right: you > have to make sure to shut it down when appropriate. > > > In general, try to avoid spawning your own thread. > > I agree, which is why I recommend using a thread pool. Yes, you are > still technically spawning your own threads (the container will not do > it for you), but the point is that you will not be spawning a thread for > each request. > > Set up your thread pool to have a "reasonable" number of threads for > your application. You do not want to have loads of users submit jobs > that will each spawn a new thread. If you run out of threads in the > thread pool, you simply tell the user to come back later. Management of > this type of resource is essential to maintaining a stable and useful > system. > > - -chris > > -BEGIN PGP SIGNATURE- > Version: GnuPG v1.4.6 (MingW32) > Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org > > iD8DBQFFvgK+9CaO5/Lv0PARAoIFAJ45DgOyFV9qxS2e+Qt9uHNTtkWpywCdHbnq > pltJVjDsmhZMg0143155k7M= > =pbEp > -END PGP SIGNATURE- > > - > To start a new topic, e-mail: users@tomcat.apache.org > To unsubscribe, e-mail: [EMAIL PROTECTED] > For additional commands, e-mail: [EMAIL PROTECTED] > > -- http://dannyayers.com - To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: Can servlets safely spawn threads?
If you are spawning threads from your servlet, make sure that they are cleaned up when the servlet is destroyed. Otherwise, you will have a thread leak. I have ran into this problem when the webapp is reloaded without restarting the server. Each leaked thread has a reference to its classloader, preventing that classloader from being garbage collected. Reload enough time will run the perm space out of memory. Bill On 1/29/07, Christopher Schultz <[EMAIL PROTECTED]> wrote: -BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Danny, David Delbecq wrote: > 1) Your servlet must always take care to finish all Threads it has > spawned. This mean when servlet gets unloaded, you must have provided a > mecanism in your servlet to stop all running threads your servlet has > created. Remaining Threads not handled by container can either cause > tomcat to not stop when requested or prevent garbage collecting of > webapp when reloading. Consider using an existing thread pool component. It should have a graceful shutdown capability already built into it. David is right: you have to make sure to shut it down when appropriate. > In general, try to avoid spawning your own thread. I agree, which is why I recommend using a thread pool. Yes, you are still technically spawning your own threads (the container will not do it for you), but the point is that you will not be spawning a thread for each request. Set up your thread pool to have a "reasonable" number of threads for your application. You do not want to have loads of users submit jobs that will each spawn a new thread. If you run out of threads in the thread pool, you simply tell the user to come back later. Management of this type of resource is essential to maintaining a stable and useful system. - -chris -BEGIN PGP SIGNATURE- Version: GnuPG v1.4.6 (MingW32) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFFvgK+9CaO5/Lv0PARAoIFAJ45DgOyFV9qxS2e+Qt9uHNTtkWpywCdHbnq pltJVjDsmhZMg0143155k7M= =pbEp -END PGP SIGNATURE- - To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: Can servlets safely spawn threads?
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Danny, David Delbecq wrote: > 1) Your servlet must always take care to finish all Threads it has > spawned. This mean when servlet gets unloaded, you must have provided a > mecanism in your servlet to stop all running threads your servlet has > created. Remaining Threads not handled by container can either cause > tomcat to not stop when requested or prevent garbage collecting of > webapp when reloading. Consider using an existing thread pool component. It should have a graceful shutdown capability already built into it. David is right: you have to make sure to shut it down when appropriate. > In general, try to avoid spawning your own thread. I agree, which is why I recommend using a thread pool. Yes, you are still technically spawning your own threads (the container will not do it for you), but the point is that you will not be spawning a thread for each request. Set up your thread pool to have a "reasonable" number of threads for your application. You do not want to have loads of users submit jobs that will each spawn a new thread. If you run out of threads in the thread pool, you simply tell the user to come back later. Management of this type of resource is essential to maintaining a stable and useful system. - -chris -BEGIN PGP SIGNATURE- Version: GnuPG v1.4.6 (MingW32) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFFvgK+9CaO5/Lv0PARAoIFAJ45DgOyFV9qxS2e+Qt9uHNTtkWpywCdHbnq pltJVjDsmhZMg0143155k7M= =pbEp -END PGP SIGNATURE- - To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: Can servlets safely spawn threads?
En l'instant précis du 01/29/07 11:33, Danny Ayers s'exprimait en ces termes: > Hi, > > I would be grateful is someone could answer these questions: > > * Can servlets safely spawn threads? short answer, yes. They *can*. However that does not mean all spawned Threads are safe. > > * If so, under what conditions? 1) Your servlet must always take care to finish all Threads it has spawned. This mean when servlet gets unloaded, you must have provided a mecanism in your servlet to stop all running threads your servlet has created. Remaining Threads not handled by container can either cause tomcat to not stop when requested or prevent garbage collecting of webapp when reloading. 2) Never have your spawned thread access request-time specific informations. This mean no request/response object passed to spawned threads. Avoid passing the Session object too. Lots of stuffs exposed by tomcat to servlet are assuming only one thread will work on it, the http thread, as such, there is quite a good amount of possible use of ThreadLocal variables. 3) if possible, spawn daemon threads, and name your threads, this ease a lot debugging. I have seen working web application spawning their own thread. Applications using the Quartz scheduler are an example of them. The Quartz scheduler spawns a few threads a provides mecanism for servlet to stop them. In general, try to avoid spawning your own thread. however, it's not always possible, and the Specs does not forbid spawning thread. But handle them properly. The best way, if you need your own thread, is to never use in the spawned thread object managed byt the container. > > I tried to find the answers searching the web, but found conflicting > views. > So I thought it worth asking about a specific servlet container > implemention. > > I'm trying to make a very simple asynchronous messaging system on top of > HTTP. What I have in mind requires that the servlet called would complete > the request-response in "reasonable" time, yet may initiate other > processes > that are potentially long-running. The easiest approach would be to > have the > servlet spawning another thread in which to run the other process, and > return a response to the client immediately. But is this possible without > running straight into concurrency breakage? > > More background at : > > http://dannyayers.com/2007/01/28/a-servlets-problem > > Thanks, > Danny. > - To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Can servlets safely spawn threads?
Hi, I would be grateful is someone could answer these questions: * Can servlets safely spawn threads? * If so, under what conditions? I tried to find the answers searching the web, but found conflicting views. So I thought it worth asking about a specific servlet container implemention. I'm trying to make a very simple asynchronous messaging system on top of HTTP. What I have in mind requires that the servlet called would complete the request-response in "reasonable" time, yet may initiate other processes that are potentially long-running. The easiest approach would be to have the servlet spawning another thread in which to run the other process, and return a response to the client immediately. But is this possible without running straight into concurrency breakage? More background at : http://dannyayers.com/2007/01/28/a-servlets-problem Thanks, Danny. -- http://dannyayers.com
