java - Report back progress of long request on Google Appengine -


i'm working on implementing web application, google appengine backend, on expected behaviour follows:

  1. user selects couple of parameters complex analysis
  2. user presses 'start'
  3. an empty 'response' page returned user, processing continues
  4. the analysis somehow continues on server , partial results being computed shown / added in response page.

i'm expecting total computation around 30-40 seconds (so way under 60 seconds required appengine).

steps 1 , 2 trivial. know step 4 somehow completed using step ajax, i'm not sure how implement step 3.

thanks!

you can use task queue , datastore. need 3 handlers:

  1. the task handler, doing hard work. store progress in datastore.
  2. a handler starts task in background , returns 'blank' page
  3. a handler status

note: page cannot blank. must have javascript on checks status. think true channel api too.

anyway heres code in python:

class longtaskstatus(ndb.model):   is_complete = ndb.booleanproperty()   percentage = ndb.floatproperty()   messages = ndb.stringproperty(repeated=true)  class longtaskhandler(webapp2.requesthandler):   def get(self):      # query existing status model or create new 1      # work ...      # update progress     status = longtaskstatus()     status.messages.appen('still busy...')     status.put()      # work ...  class starthandler(webapp2.requesthandler):   def get(self):      # start task     taskqueue.add(url='/longtask')      # return page uses javascript check progress every few seconds     template = jinja_environment.get_template('taskprogress.html')     self.response.write(template.render(template_values))  class checktaskstatus(wenapp2.requesthandler):   def get(self):     query = longtaskstatus.query().fetch(1)     result = {}     if query:       status = query[0]       result = {         'is_complete': status.is_complete,         'percentage': status.percentage,         'messages': status.messages       }     self.response.write(json.dumps(result))

and heres "blank" page:

<!doctype html> <html lang="en">   <body>     <div id="status"></div>     <script>       window.setinterval(function(){         $.get( "ajax/test.html", function( data ) {           $( ".status" ).html( data );         });       }, 5000);     </script>   </body> </html>

edit: other option without task queue

if have unique way of identifying task before started potentially speed method not using task queue api.

heres how:

  1. call longtaskhandler via javascript
  2. redirect loading page, calls checktaskstatus.

this should faster using task queues, unfortunately need way identify task before started. eg userid, session etc


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