2014-01-30 Daniel Mikusa <dmik...@gopivotal.com>: > On Jan 30, 2014, at 11:18 AM, Yann Simon <yann.simon...@gmail.com> wrote: > >> Hi, >> >> I wrote a sample app to demonstrate the problem: >> https://github.com/yanns/servlet31_async >> >> You can generate an exploded war with maven: mvn war:exploded >> I deployed the application in tomcat 8.0.0-RC10. >> >> The 2 upload form does work. >> The 1st upload form uses a new thread in , and that does not work. >> https://github.com/yanns/servlet31_async/blob/master/src/main/java/com/yann/ReadListenerImpl.java#L22 > > I’m not sure I see the point of the code here. If you force it to block with > Thread.sleep() you’re going to tie up the thread that you’ve created and > you’re going to be back to having threads sitting around and doing nothing. > If that’s the case, you may as well save yourself some trouble and use the > blocking apis.
This sample application is only a simple way to show what I want to achieve with a more complex application that I mentioned at the beginning of the thread: https://github.com/yanns/play2-war-plugin/blob/servlet31/project-code/core/servlet31/src/main/scala/play/core/server/servlet31/RequestHandler31.scala#L80 Let me try to explain the use case: let's say we want to save the uploaded file chunk by chunk in a database, for which we have an asynchronous API. - we receive the first chunk, that we can read synchronously in onDataAvailable, no problem so far - we trigger the saving of this chunk in the database, and of course, we do not wait for the completion of the operation - we receive the signal that a new chunk is available - the container call onDataAvailable - we cannot push this chunk into the database, as the first operation is not completed - we asynchronously wait for the completion of the database operation. We do not read any data so that the container push the pressure back to the browser, telling it to slowdown. We do not want to block any thread here. That's why we must exit the onDataAvailable without having read any data. - when the database says us that it is ready for a new operation (by a callback, or an event), then we can read the second chunk and trigger the save operation in the database This a what I simulated with the new Thread and Thread.sleep. In reality, there are no "new Thread" - it just simulates that at some point later, the database driver informs us that the database is ready for a new operation. There are no Thread.sleep neither - it just simulates a slow database to check the back-pressure mechanism that the container should do on the browser. Also, if you said that I must consume the chunks synchronously in onDataAvailable, I can simply not implement this double triggering (from browser and from database) without blocking any thread. For me, it means that I cannot totally use the asynchronous IO mechanism of the OS. I hope I made my goals clear. Cheers, Yann > > Here’s what I’d suggest to make this work. > > - in onDataAvailable read as much data as possible > - if you read until input.isReady() is false then just exit the function. > The container will call back when more data can be read. > - if you need to stop reading for some reason but input.isReady() is still > true, use a thread pool to schedule your own call back to onDataAvailable at > some point in the future. You can then continue reading at that point in > time. > - Repeat until you’ve read all the data. > > You still need additional threads with this approach, but it’s not one to > one. A small thread pool can service many requests because the thread is > only active when data is being read. > > Here’s an example of this in action. > > > http://git.eclipse.org/c/jetty/org.eclipse.jetty.project.git/tree/jetty-servlets/src/main/java/org/eclipse/jetty/servlets/DataRateLimitedServlet.java > > Dan > >> >> The "onDataAvailable" is called only one time. >> >> With jetty, it does work (mvn jetty:run) >> >> I hope this can help. >> >> Yann >> >> 2014-01-08 Yann Simon <yann.simon...@gmail.com>: >>> 2014/1/8 Daniel Mikusa <dmik...@gopivotal.com>: >>>> On Jan 8, 2014, at 12:04 PM, Yann Simon <yann.simon...@gmail.com> wrote: >>>> >>>>> Hi, >>>>> >>>>> I am trying to write a servlet that asynchronously read data from the >>>>> servlet request input stream. >>>>> I tested my servlet with tomcat 8.0.0-RC5. >>>> >>>> If possible, you might want to try 8.0.0-RC10 or trunk and see if you're >>>> getting the same behavior. >>>> >>>>> >>>>> the symptoms: >>>>> - I must synchronously read the input stream in onDataAvailable() so >>>>> that the upload works >>>>> >>>>> what I expected: >>>>> I want to be more "reactive" (buzzword of the moment) and not read the >>>>> input stream until I am ready (=until the previous chunk is processed) >>>>> I though I could return from onDataAvailable() before having read all >>>>> the data, read the data in another thread. >>>> >>>> Do you have a code sample? It would help to see what you're doing. >>>> >>>>> I expected onDataAvailable() to be called again when I consumed all the >>>>> data >>>>> (servletInputStream.isReady becomes false) >>>> >>>> Generally this sounds OK. When you call ServletInputStream.isReady() and >>>> it returns false, that should trigger the container to call >>>> onDataAvailable() when more data is available to be read. If you return >>>> from onDataAvailable() and ServletInputStream.isReady() is still true the >>>> container won't call onDataAvailable() again. You'll be responsible for >>>> calling it when you're ready to read more. >>>> >>>>> That way, I could implement back pressure on the browser as long as my >>>>> servlet has not finished its work with the actual chunk >>>>> >>>>> But if I do that, neither onDataAvailable() nor onAllDataRead() is called >>>>> again. >>>> >>>> Again, a code sample would be helpful. Debugging non-blocking IO is >>>> tricky. If you can include a sample Servlet or test case, it would >>>> greatly increase your chance of getting feedback. >>> >>> Thanks for the quick answer! >>> >>> I have a code sample, but it may be too complicated to help debugging >>> the problem. >>> It is written in Scala. Its purpose is to provide a servlet that runs >>> asynchronous action from Playframework (http://www.playframework.com/) >>> >>> https://github.com/yanns/play2-war-plugin/blob/servlet31/project-code/core/servlet31/src/main/scala/play/core/server/servlet31/RequestHandler31.scala#L74 >>> >>> The line 80 (iteratee = iteratee.pureFlatFold ) use a closure that >>> consumes the input stream asynchronously in another thread. >>> >>> I'll try to take the time to write a much simpler code sample in Java. >>> >>>> >>>> Dan >>>> >>>>> >>>>> When I consume the input stream synchronously in onDataAvailable(), it >>>>> works as expected. >>>>> >>>>> Am I misunderstanding the asynchron IO in Tomcat 8? >>>>> >>>>> Thanks in advance for any ideas! >>>>> Yann >>>>> >>>>> --------------------------------------------------------------------- >>>>> To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org >>>>> For additional commands, e-mail: users-h...@tomcat.apache.org >>>>> >>>> >>>> >>>> --------------------------------------------------------------------- >>>> To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org >>>> For additional commands, e-mail: users-h...@tomcat.apache.org >>>> >> >> --------------------------------------------------------------------- >> To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org >> For additional commands, e-mail: users-h...@tomcat.apache.org >> > > > --------------------------------------------------------------------- > To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org > For additional commands, e-mail: users-h...@tomcat.apache.org > --------------------------------------------------------------------- To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
