dflorey and Pieter, thank you for the links, I will look into it asap.
On Jul 12, 10:35 pm, Pieter Coucke <[email protected]> wrote: > You can check request headers to see if this is a first invocation of a task > (http://code.google.com/appengine/docs/java/taskqueue/overview.html#Ta...), > so you can detect a second invocation of a task. > > Maybe if you combine this with specific catch blocks for mail exceptions? > > > > On Mon, Jul 12, 2010 at 10:07 PM, Marcus Brody <[email protected]> wrote: > > Pieter, > > > although this looks easy its not that easy, I am aware that I can > > queue a mail sending task, > > problem is that task has to be idempotent to achiev desired behaviour, > > > a queue task can be executed for example twice, since those are > > specifications > > and this would result in sending mail twice, > > a naive aproach would be to update some db lock to prevent sending > > mail more than 1 time, > > but it is not easy, this is much more complicated, > > in other words operation is either atomic or it isnt, and without very > > precise mechanism you > > cannot prove that task will be runned only one. > > > My own tests proved that due to email quota being reached (task fail > > and has be resheduled) some of the mails > > has been send twice. > > > If Mail API would allowed to send mail only in case of some db > > transaction success it would be very easy to garant > > that mail will be send exactly 1 time. (although if it fails for some > > other reasons like recipient not found or so thats whole another > > story :) > > > Basically this can be solved by > > 1) adding new API for sending mail (dont know if it so easy or whole > > problem isnt much much bigger than i think - distributed > > transactions ?) > > 2) implementing locking mechanism > > > On Jul 12, 9:13 pm, Pieter Coucke <[email protected]> wrote: > > > Create a task for sending e-mail instead of calling the mailservice > > > directly. > > > > use this in your task (a task can be part of a transaction) > > > > try{ > > > ... > > > > } catch (Throwable thr) { > > > log.error(...); > > > } > > > > and all exceptions will be catched. I think a task will be re-executed > > only > > > if it fails (throws an exception). > > > > On Sat, Jul 10, 2010 at 6:43 PM, Marcus Brody <[email protected]> > > wrote: > > > > Hello, > > > > > I would like to ask, if there is some way how to send mail only in > > > > case that some db transaction will be successful. > > > > I am not very experienced with gae, but I did study it now for about 2 > > > > weeks. > > > > > Desired output: > > > > > 1) prepare email > > > > 2) db transaction.begin() > > > > 3) do some db operation > > > > 4) bind sending mail with current transaction (similar to > > > > how can you can attach Task to queue) > > > > 5) db transaction.commit() > > > > > I am aware that I can queue mail sending task to task queue, but i > > > > cannot find the way how to do that mail sending task Idempotent > > > > without (i think) complicated locking mechanism . > > > > Most simple solution would be to put mail sending task to task queue, > > > > but this means mail could be send twice in some rare situation. (this > > > > is maybe not that bad but if there is some way how to avoid it, I > > > > would like to know) > > > > > Thank you, > > > > > Marcus > > > > > -- > > > > 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 > > > > [email protected]. > > > > To unsubscribe from this group, send email to > > > > [email protected]<google-appengine-java%[email protected]> > > <google-appengine-java%[email protected]<google-appengine-java%[email protected]> > > > > > . > > > > For more options, visit this group at > > > >http://groups.google.com/group/google-appengine-java?hl=en. > > > > -- > > > Pieter Coucke > > > Onthoo BVBAhttp://www.onthoo.comhttp://www.koopjeszoeker.be > > > -- > > 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 > > [email protected]. > > To unsubscribe from this group, send email to > > [email protected]<google-appengine-java%[email protected]> > > . > > For more options, visit this group at > >http://groups.google.com/group/google-appengine-java?hl=en. > > -- > Pieter Coucke > Onthoo BVBAhttp://www.onthoo.comhttp://www.koopjeszoeker.be -- 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 [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/google-appengine-java?hl=en.
