I forgot to ask something:
You said that the LinkedBlokingQueue is on the whitelist and should work on
GAE.
What is the way to pass the object betwean the JVMs/processes ?
I use the memcache and it does not solve my problem.
Cache cache;
try {
cache =
CacheManager.getInstance().getCacheFactory().createCache(Collections.emptyMap());
Semaphore toModemSem = (Semaphore)cache.get("toModemSem");
if (toModemSem == null) {
log.info("memcache returns null");
toModemSem = new Semaphore(0);
cache.put("toModemSem", toModemSem);
}
toModemSem.release();
...
Sorry my example is about the Semaphore. But I do the same with
LinkedBlokingQueue the queue. And both does not work.
Do I use the memcache correctly ?
On Sat, Jan 29, 2011 at 9:47 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
>> >
>> >
>>
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