Yes, you are right.
It takes 400-600ms so it costs about an hour of the cpu time per 24hours.
It is acceptable.
I DO it following way:
Map<Object, ToModemInfoEntity> entity;
try {
for (int i=0; i<100; i++) {
entity = ofy.get(ToModemInfoEntity.class);
if (entity != null && !entity.isEmpty()) {
log.info("got data from db, do my stuff here...");
} else {
Thread.sleep(100);
}
}
}
Can I improove anything else, please ?
On Sun, Jan 30, 2011 at 1:36 PM, Didier Durand <durand.did...@gmail.com>wrote:
> PS: you should also combine memcache + ds datastore to reduce cpu.
>
> regards
>
> didier
>
> On Jan 30, 1:10 pm, Artur Downar <artur.dow...@googlemail.com> wrote:
> > So, you mean polling on the database.
> >
> > I wrote:
> >
> > try {
> > for (int i=0; i<100; i++) {
> > entity = ofy.find(ToModemInfoEntity.class, "whatever");
> > if (entity != null) {
> > log.info("got data from db, do my stuff here...");
> > } else {
> > Thread.sleep(100);
> > }
> > }
> > }catch (Throwable th) {
> > th.printStackTrace();
> > }
> >
> > It is cpu-time consuming.
> > It polls for about 11seconds and it takes about 1500ms of the cpu time.
> > It makes more than 2hours of the CPU time per natural day.
> >
> > I can extend the Time.sleep(period) but it still seems unacceptable due
> to
> > CPU costs.
> >
> > On Sun, Jan 30, 2011 at 8:21 AM, Didier Durand <durand.did...@gmail.com
> >wrote:
> >
> > > Sorry,
> >
> > > hit "send" too quicly
> >
> > > b) why don't you do something like this
> >
> > > Side reading data:
> > > ==================
> >
> > > do {
> > > read new data from ds;
> > > if (new data) {
> > > mark data as read in ds
> > > do what you need
> > > return;
> > > } else {
> > > Thread.sleep(100)
> > > }
> > > } until (running time near 30s)
> > > if (no new data) {
> > > give error message to waiting user
> > > }
> >
> > > Side writing data
> > > ==================
> >
> > > write new data to datastore (with corresponding status showing that
> > > it's new and not read yet)
> >
> > > N.B: the 30s is a hard limit imposed by gae. You've to check for it
> > > and end gracefully else your servlet will be killed by GAE.
> >
> > > regards
> >
> > > didier
> >
> > > On Jan 30, 8:15 am, Didier Durand <durand.did...@gmail.com> wrote:
> > > > Hi,
> >
> > > > To answer your questions:
> >
> > > > a) yes, you can say how long you waits Thread.sleep(millis) where
> > > > millis says how many milliseconds you want to wait
> >
> > > > b) why don't you do something like this
> >
> > > > do {
> > > > read new data from ds;
> >
> > > > }
> >
> > > > On Jan 29, 10:38 pm, Stephen Johnson <onepagewo...@gmail.com> wrote:
> >
> > > > > At the moment the Channel API is javascript only. There are a lot
> of
> > > people
> > > > > that would like it to be open to other languages for things just
> like
> > > you
> > > > > want to do. You might be able to use something like Rhino to run
> the
> > > > > javascript in Java but not sure if that will work. You should take
> a
> > > look at
> > > > > XMPP, it's very simple to have the server send instant messages. I
> did
> > > a
> > > > > quick search for XMPP libraries in Java and here is one I found.
> I'm
> > > sure
> > > > > there are many others. Check outhttp://
> > > twit88.com/blog/2009/02/17/java-xmpp-client-library/
> > > > > On Sat, Jan 29, 2011 at 2:07 PM, Artur Downar
> > > > > <artur.dow...@googlemail.com>wrote:
> >
> > > > > > Thank you.
> >
> > > > > > I took a brief look on channel API and it seems I it is the thing
> I
> > > need.
> >
> > > > > > I have a small question.
> >
> > > > > > The modem device is a java embedded device and it has no public
> IP.
> > > There
> > > > > > is no javascript on it. Only java.
> >
> > > > > > Is it enough for GAE channel API to communicate with it ?
> >
> > > > > > On Sat, Jan 29, 2011 at 9:49 PM, Stephen Johnson <
> > > onepagewo...@gmail.com
> > > > > > > wrote:
> >
> > > > > >> Sounds like you need more of a Push style. Checkout the Channel
> API
> > > or the
> > > > > >> XMPP api.
> >
> > > > > >> On Sat, Jan 29, 2011 at 1:47 PM, Artur Downar <
> > > > > >> artur.dow...@googlemail.com> wrote:
> >
> > > > > >>> The external device polls for data from GAE.
> > > > > >>> It is not specified when the data arrives. To describe it more
> > > clearly.
> > > > > >>> The device is a GSM modem device that sends an SMS on the user
> > > request.
> >
> > > > > >>> The user launches a web browser and writes a mobile phone
> number.
> > > The
> > > > > >>> browser sends data to the GAE and the sms should be send
> > > immediately
> >
> > > > > >>> So I cannot specify how long I can wait in Thread.sleep().
> >
> > > > > >>> You mention about Objectify. I use that library but I'm quite
> new
> > > to it.
> >
> > > > > >>> Does it have the mechanism that works like:
> >
> > > > > >>> process A waits for data until data into database arrives or
> > > timeout
> > > > > >>> expires
> > > > > >>> process B puts the data into database
> > > > > >>> process a continues processing the data inserted by process B
> >
> > > > > >>> ?
> >
> > > > > >>> On Sat, Jan 29, 2011 at 3:59 PM, Didier Durand <
> > > durand.did...@gmail.com>wrote:
> >
> > > > > >>>> Hi,
> >
> > > > > >>>> Forgot: you can use Thread.sleep() to wait (java.lang.Thread
> is
> > > also
> > > > > >>>> part of the JRE)
> >
> > > > > >>>> regards
> >
> > > > > >>>> didier
> >
> > > > > >>>> On Jan 29, 3:35 pm, Didier Durand <durand.did...@gmail.com>
> > > wrote:
> > > > > >>>> > Hi,
> >
> > > > > >>>> > LinkedBlokingQueue is part of JRE WhiteList:
> > > > > >>>>http://code.google.com/appengine/docs/java/jrewhitelist.html.
> So,
> > > you
> > > > > >>>> > can use it.
> >
> > > > > >>>> > But, I dont see the need. Why don't you just from on the
> > > datastore on
> > > > > >>>> > 1 side and read from it on the other. It would be very
> simple
> > > and rely
> > > > > >>>> > on the most basic (i.e solid) mechanism of gae. (I would
> > > recommend
> > > > > >>>> > Objectify for ds read/ write)
> >
> > > > > >>>> > As you have network round-trips, the read / write time will
> be
> > > > > >>>> > negligible even it can seem high compared to an in-memory
> > > mechanism
> > > > > >>>> > like a Queue.
> >
> > > > > >>>> > regards
> >
> > > > > >>>> > didier
> >
> > > > > >>>> > On Jan 29, 1:51 pm, arturad <artur.dow...@googlemail.com>
> > > wrote:
> >
> > > > > >>>> > > In my application an embedded device (no public IP) should
> > > connect
> > > > > >>>> to
> > > > > >>>> > > the GAE in order to obtain some data from it. The data are
> > > provided
> > > > > >>>> by
> > > > > >>>> > > the web browser.
> >
> > > > > >>>> > > The whole data-passing process looks like:
> >
> > > > > >>>> > > web browser
> ->
> > > GAE ->
> > > > > >>>> > > embedded standalone device
> >
> > > > > >>>> > > I developed a servlet the device connects to. It issues
> the
> > > HTTP
> > > > > >>>> GET.
> > > > > >>>> > > On the other side the web browser sends data using
> standard
> > > GWT
> > > > > >>>> > > RemoteServiceServlet.
> >
> > > > > >>>> > > In case there is no data for the device the doGet method
> in
> > > the
> > > > > >>>> > > servlet should stop for some seconds until user enters
> data or
> > > time
> > > > > >>>> > > out expires.
> >
> > > > > >>>> > > I'm trying to use LinkedBlockingQueue to pass data
> between
> > > two
> > > > > >>>> > > servlets. It does not work unfortunately. Seems like the
> GAE
> > > > > >>>> launches
> > > > > >>>> > > new JVM for concurrent requests... I pushed the
> > > LinkedBlockingQueue
> > > > > >>>> > > into memcache and get it by name from concurrent requests.
> > > Still
> > > > > >>>> does
> > > > > >>>> > > not work. Memcache returns NOTnull. But there are no data
> in
> > > the
> > > > > >>>> > > queue.
> >
> > > > > >>>> > > In order to investigate my issue I've made some tests with
> the
> > > > > >>>> > > semaphore. Pushed the semaphore to the memcache and made
> some
> > > > > >>>> > > concurrent operations ... -> does not work -> one process
> does
> > > not
> > > > > >>>> > > release the other...
> >
> > > > > >>>> > > The problem occurs on GAE only. The whole mechanism works
> on
> > > the
> > > > > >>>> > > development server.
> >
> > > > > >>>> > > Is there any way to stop/freeze one process (in the doGet
> > > method in
> > > > > >>>> > > servlet) and unblock it by another one ?
> >
> > > > > >>>> > > Or... Is there any other way to solve my problem ?
> > > > > >>>> > > Thank you for any suggestions.
> > > > > >>>> > > Artur
> >
> > > > > >>>> --
> > > > > >>>> You received this message because you are subscribed to the
> Google
> > > > > >>>> Groups "Google App Engine for Java" group.
> > > > > >>>> To post to this group, send email to
> > > > > >>>> google-appengine-java@googlegroups.com.
> > > > > >>>> To unsubscribe from this group, send email to
> > > > > >>>> google-appengine-java+unsubscr...@googlegroups.com<google-appengine-java%2bunsubscr...@googlegroups.com>
> <google-appengine-java%2bunsubscr...@googlegroups.com<google-appengine-java%252bunsubscr...@googlegroups.com>
> >
> > > <google-appengine-java%2bunsubscr...@googlegroups.com<google-appengine-java%252bunsubscr...@googlegroups.com>
> <google-appengine-java%252bunsubscr...@googlegroups.com<google-appengine-java%25252bunsubscr...@googlegroups.com>
> >
> >
> > > > > >>>> .
> > > > > >>>> For more options, visit this group at
> > > > > >>>>http://groups.google.com/group/google-appengine-java?hl=en.
> >
> > > > > >>> --
> > > > > >>> You received this message because you are subscribed to the
> Google
> > > Groups
> > > > > >>> "Google App Engine for Java" group.
> > > > > >>> To post to this group, send email to
> > > > > >>> google-appengine-java@googlegroups.com.
> > > > > >>> To unsubscribe from this group, send email to
> > > > > >>> google-appengine-java+unsubscr...@googlegroups.com<google-appengine-java%2bunsubscr...@googlegroups.com>
> <google-appengine-java%2bunsubscr...@googlegroups.com<google-appengine-java%252bunsubscr...@googlegroups.com>
> >
> > > <google-appengine-java%2bunsubscr...@googlegroups.com<google-appengine-java%252bunsubscr...@googlegroups.com>
> <google-appengine-java%252bunsubscr...@googlegroups.com<google-appengine-java%25252bunsubscr...@googlegroups.com>
> >
> >
> > > > > >>> .
> > > > > >>> For more options, visit this group at
> > > > > >>>http://groups.google.com/group/google-appengine-java?hl=en.
> >
> > > > > >> --
> > > > > >> You received this message because you are subscribed to the
> Google
> > > > > >> Groups "Google App Engine for Java" group.
> > > > > >> To post to this group, send email to
> > > > > >> google-appengine-java@googlegroups.com.
> > > > > >> To unsubscribe from this group, send email to
> > > > > >> google-appengine-java+unsubscr...@googlegroups.com<google-appengine-java%2bunsubscr...@googlegroups.com>
> <google-appengine-java%2bunsubscr...@googlegroups.com<google-appengine-java%252bunsubscr...@googlegroups.com>
> >
> > > <google-appengine-java%2bunsubscr...@googlegroups.com<google-appengine-java%252bunsubscr...@googlegroups.com>
> <google-appengine-java%252bunsubscr...@googlegroups.com<google-appengine-java%25252bunsubscr...@googlegroups.com>
> >
> >
> > > > > >> .
> > > > > >> For more options, visit this group at
> > > > > >>http://groups.google.com/group/google-appengine-java?hl=en.
> >
> > > > > > --
> > > > > > You received this message because you are subscribed to the
> Google
> > > Groups
> > > > > > "Google App Engine for Java" group.
> > > > > > To post to this group, send email to
> > > > > > google-appengine-java@googlegroups.com.
> > > > > > To unsubscribe from this group, send email to
> > > > > > google-appengine-java+unsubscr...@googlegroups.com<google-appengine-java%2bunsubscr...@googlegroups.com>
> <google-appengine-java%2bunsubscr...@googlegroups.com<google-appengine-java%252bunsubscr...@googlegroups.com>
> >
> > > <google-appengine-java%2bunsubscr...@googlegroups.com<google-appengine-java%252bunsubscr...@googlegroups.com>
> <google-appengine-java%252bunsubscr...@googlegroups.com<google-appengine-java%25252bunsubscr...@googlegroups.com>
> >
> >
> > > > > > .
> > > > > > For more options, visit this group at
> > > > > >http://groups.google.com/group/google-appengine-java?hl=en.
> >
> > > --
> > > You received this message because you are subscribed to the Google
> >
> > ...
> >
> > read more ยป
>
> --
> You received this message because you are subscribed to the Google Groups
> "Google App Engine for Java" group.
> To post to this group, send email to
> google-appengine-java@googlegroups.com.
> To unsubscribe from this group, send email to
> google-appengine-java+unsubscr...@googlegroups.com<google-appengine-java%2bunsubscr...@googlegroups.com>
> .
> For more options, visit this group at
> http://groups.google.com/group/google-appengine-java?hl=en.
>
>
--
You received this message because you are subscribed to the Google Groups
"Google App Engine for Java" group.
To post to this group, send email to google-appengine-java@googlegroups.com.
To unsubscribe from this group, send email to
google-appengine-java+unsubscr...@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/google-appengine-java?hl=en.
